The Outermost Planet?

Neptune may be the outermost planet. After the torridity of having to refer to the previous planet by a silly name or bear the brunt of using an unofficial name, it’s nice to have the calm of just being able to call it “Neptune” without the irritation of puerile jokes. That said, things could’ve turned out very differently because one of the names considered for the seventh planet was actually Neptune!

The two planets are the most similar pair in the entire system. That said, having fixated on Hamlet for so long, right now the two don’t look that alike to me. Neptune has no obvious rings, spins more upright and is a much clearer and more vivid (livid?) blue than the hazy and almost featureless Hamlet. The further out a gas giant is, the more likely it is, even if bigger than Jupiter, to look like Neptune. If Tyche exists, it will be blue, and outer planets in other star systems whose stars provide less radiation than about a thousandth of solar intensity at our distance from it are also probably going to look like this, although much dimmer. The above image is actually more colourful than it would look to the unaided human eye, at least at first. At Neptune’s distance, the Sun is nearly a thousand times dimmer than at Earth’s. The logarithmic nature of senses means that this wouldn’t seem as dim as that suggests. It’s still about 360 times brighter than Cynthia ever gets. Moonlight is insufficient to make out colour, but I don’t know about sunlight on Neptune. In a way it’s odd even to consider what colour Neptune would look like to human vision as nobody will ever see it in person and it would appear to be coloured to some species who live on this planet, particularly nocturnal ones.

The Titius-Bode series does not apply to Neptune. It’s actually 30.1 AU from the Sun rather than the predicted 38.8, although Pluto is much closer to that distance. That doesn’t mean Pluto is or isn’t a planet by the way, but that astronomers expected there to be one there and therefore called it one. What’s actually happening there is quite interesting, but I’ll leave that for now. Neptune was discovered in 1846, by which time a large number of asteroids had also been found and Ceres was no longer considered a planet, which led to the idea that Bode’s Law was mere coincidence. The revision which was able to include Hamlet’s major satellites could be seen, again, as a form of pareidolia, where an increasingly vague formula is used to fit observed phenomena which actually doesn’t reflect any real process or effect but just corresponds to the various coincidences. The sequence was originally n+4, with n=0 for Mercury, rather than a simple doubling sequence, and the fact that the asteroid belt intervenes and Neptune doesn’t fit makes the idea that it’s an actual law more doubtful because there are then three out of ten exceptions to the rule. A side issue, probably not important, is the surprising convenience of Earth being at a round ten units from the Sun. The question arises, then, of whether there really is something about Neptune which puts it in the “wrong” place or whether it’s just that the spurious correlation was revealed by it. Most astronomers would agree with the latter possibility.

Neptune is not the coldest planet in the system in spite of being further from the Sun than any other known planet, at least consistently. This is because, unlike the seventh planet, it has a significant internal heat source. It takes 165 years to orbit the Sun, and having a moderate axial tilt this gives the temperate regions four-decade-long seasons. The axial tilt is 28° and the day lasts sixteen hours, which is technically close to Hamlet’s but differs in that the poles don’t spend most of their time pointing towards or away from the Sun. It might therefore be expected to have seasons dominated by the Sun, but this isn’t obvious because unlike its twin, Neptune is heated internally. This leads to Neptune being warmer than the other ice giant at cloud top level. Like the other outer planets, this heat is due to contraction of the planet from the part of the solar nebula it formed from, but in Neptune’s case there may be an extra factor in the form of its large moon Triton’s tidal influence. The centre is at around 7000°C compared to the other giant’s 5000, possibly because Neptune wasn’t disrupted, but it could also be that both planets go through warmer and colder phases and we happen to be living at a time when it’s that way round. I don’t actually know how they arrived at these figures considering that there are theories that the clouds are cold due to insulating convection layers, meaning that heat doesn’t leak out and is therefore presumably undetectable, but this is what they say. Neptune’s centre is therefore hotter than the surface of the Sun.

Regardless of the temperature at the core, the cloud tops are still very cold at around -200°C. Before Voyager 2 got there, it was speculated that the low temperature could give rise to fast winds in the atmosphere because the vibration of gas molecules at higher temperatures was absent, leading to a low-friction environment, and this did in fact turn out to be so. The winds are the fastest recorded in the system at over 2000 kph. At the equator, the average wind speed is around 1100 kph, which is about the same as the speed of sound at sea level on Earth. On Earth, the Coriolis Effect is somewhat significant in generating wind but the main driver is the primary or secondary solar heating and cooling. The Sun heats the air on this planet, causing it to expand, or cooler areas have contracting air over them, allowing the warmer air to move in and occupy the space due to the pressure difference, or in a more complicated process, land and water change temperature at different rates, causing air movement. Although the core of Neptune is far hotter than its exterior, this doesn’t seem to drive the extreme high velocity winds near the cloud tops. My guess is that it’s somewhat similar to a perpetual motion machine, which of course cannot exist. The input from whatever source to the weather systems, such as the Coriolis Effect, tidal forces and the hot interior of the planet, puts the atmosphere in motion and due to the lack of friction that energy is only lost very slowly, and consequently the winds accelerate until they reach the speed of sound, which prevents them from moving any faster. This is not a detailed explanation and may well be completely incorrect. It’s just a guess.

Neptune has more visible banding than the other ice giant, and also has rotating storms in its atmosphere which have been observed to last up to six years. This is far less durable than Jupiter’s storms, but the size and energy input are smaller so this might be expected. Neptune’s Great Dark Spot is visible in the lower part of the picture at the start of this post, but here it is again:

The spot was 13 000 kilometres long by 6 000 wide, and is a hole in the cloud deck. The white clouds around it are cirrus made of frozen methane and were instrumental in enabling the wind speed to be measured. It’s thought that the spots disappear as they approach the equator, which can take years. As I may have mentioned before, the Great Dark Spot was at the same latitude as Jupiter’s Great Red Spot, and this suggests it’s recurrent. If it is, it also shares with the GRS a tendency to appear and disappear. I’ve mentioned elsewhere that it seems to be more than coincidence that planets tend to have a fluid-related feature at this latitude, including Hawaiʻi, Olympus Mons, the Great Red Spot and this storm, which is intermittent, and although I have a vague impression of a pyramid superimposed on the bodies in question with the apex at one pole, I can’t put my finger on why this would happen or whether it actually is more than cherrypicking.

Neptune’s blueness can’t be explained simply through Rayleigh scattering and there must actually be something blue in its atmosphere which isn’t in Hamlet’s, but what this is exactly is another question entirely. Even so, it is true that the methane contributes by absorbing red light. The different hydrocarbon content contributes to it being warmer than Hamlet due to a greenhouse effect, although this is only relative as it’s still at the temperature of liquid nitrogen on Earth.

This is a fairly well-known image of clouds on Neptune above the more generally blue cloud deck. These clouds are frozen methane, but the picture also seems to show that not far below them is a blue haze with a definite level top to it. The clouds are about fifty kilometres above the haze and are casting such definite shadows because the Sun is low in the sky at this point, as evinced by the night on the right hand side of the image. Although the widths of the clouds here varies between around fifty and two hundred kilometres, I don’t know how that scale compares to the clouds in our own sky. It does sound rather larger at first consideration. I’m also tempted to see them as having been streamlined by the powerful winds and feel they don’t have much chance to be wispy, unlike Earth’s cirrus clouds. They’re almost like contrails in a way.

One theory about Neptune’s clouds is that the planet’s atmosphere is effectively a giant cloud chamber. A cloud chamber is a delicately balanced humid atmosphere used to detect subatomic particles, whose energy as they move through it leaves wakes in the form of clouds. This can be created using the steam from dry ice. The planet in question is of course very cold at the height the clouds can be seen, and it’s been theorised that galactic cosmic rays stimulate the atmosphere into producing these streaks. The coolness of the atmosphere makes these things much more significant for Neptune than here, so if this is how it happens, the cause is similar to the high winds. Ultraviolet light from the Sun is also probably responsible for features in the atmosphere, but probably the haze more than the clouds.

The rate of rotation has the same features as that of the bigger gas giants, as the planet does not rotate as a solid body would. The magnetosphere can be taken as a guide to the rotation period if you like, but it isn’t necessarily any more “real” than anything else and we only think it is because we’re from a planet with a solid surface and a shallow atmosphere. The magnetosphere takes sixteen hours, the equator eighteen and the poles twelve. All of this also raises the question of whether it even means anything to assert that Neptune has powerful winds. Maybe that’s just the rotation of the planet, which varies, but it doesn’t mean they actually amount to winds just because different parts rotate at different rates. The understanding of fluid movement used with Jupiter, that they’re cylinders rotating independently, actually cancels out the idea that there are such winds, although there could still be slipstream areas where the wind would be felt.

Unsurprisingly, the interior of the planet closely resembles the other ice giant’s. As I mentioned before, Olaf Stapledon described Neptune, important in ‘Last And First Men’, thus: “. . . the great planet bore a gaseous envelope thousands of miles deep. The solid globe was scarcely more than the yolk of a huge egg.” The upper atmosphere is mainly hydrogen and helium with some methane. Deeper inside is a liquid, becoming solid, layer composed of water, ammonia and methane, and at the centre is a core somewhat larger than Earth made of silicate rock and iron. Like Hamlet, it probably rains diamonds and there are likely to be diamond-bergs floating in the ocean. There may even be a whole layer of diamond deep within the planet.

There being two similar planets of this kind in the system might be seen as coincidence, but in a cosmic context seems not to be. In fact, Neptune-like planets are more common in the Galaxy than Jupiter- or Saturn-sized ones, and the fact that only one spacecraft has ever visited either hampers understanding of a disproportionately large number of worlds. There are nearly 1 800 known Neptune-like planets, notably referred to as “Neptune-like” rather than “Uranus-like”, which makes me wonder again about that ridiculous name although Neptune is more “typical” seeming since it isn’t tipped on its side. Even more common, and absent from the known Solar System, is the intermediate-mass type of planet both smaller than Neptune and larger than Earth. Some of these are much closer to their stars than our own ice giants, and can’t therefore really be classified as such. Nonetheless, this size and mass of planet is common in the Universe.

Getting back to our own Neptune, one surprising finding was that like Hamlet’s magnetic field, Neptune’s is off-centre and at a radically different angle to its axis of rotation. This creates another puzzle because the orientation of Hamlet’s magnetosphere was attributed to its peculiar tilt and misadventure with a large body in the distant past, but given that Neptune’s is also like that suggests that this is irrelevant and makes me wonder if that ever happened, although the tilt does need to be explained. It’s offset by 55% of the planet’s radius and the magnetic poles are 47° from the axis of rotation, yet no explanation based on collisions or close encounters with large objects has been offered so far as I know.

That said, Neptune does in fact show some evidence for this. Discounting Pluto and Charon, the planet has the largest proportionate satellite of any planet in the system but Earth, namely Triton, which is also the only large moon to orbit backwards, and appears to be a captured dwarf planet. Also, the moon Nereid has a comet-like orbit with its closest approach to the planet being much greater than its greatest distance, making it elongated and highly elliptical. Hence one catastrophe may have occurred to Hamlet and another radical event to Neptune, and the question then arises of what was happening in the outer solar system early in its history. Neptunian auroræ are not distributed like terrestrial ones due to the different magnetic field and the presence of rings, which reduces the quantity of charged particles trapped in the magnetosphere. Neptune and Triton also interact magnetically in a similar manner to Jupiter and Io, although not so strongly. There are diffuse auroræ close to the equator to just over half way to the poles, and more definite rings of auroræ closer to the poles, and brighter near the south pole at the time of the Voyager 2 encounter. Neptune has the weakest magnetosphere of any gas giants.

As mentioned above, Neptune has rings. Once Jupiter’s rings had been discovered by the Voyagers, Hamlet already having had them detected, it seemed inevitable that it would have them too, and it has. They were discovered from Earth in 1984 CE but had been seen occulting a star in 1981 in a manner compatible with them not being complete. That is, it was established that there were curved objects orbiting the planet but not that they went all the way round. This is probably because their width varies more than the other three planets’. There was an uncomfortable period in the early ’80s when for me it seemed inevitable that Neptune would be ringed but there was no evidence either way on the issue. I wanted the giant planets to be uniform. For some reason its ringedness is less emphasised than the others’, maybe because it had become routine by that time and it would’ve been more surprising if it hadn’t been.

There is no uniform scheme for naming planetary rings, as can be seen with Hamlet’s. Neptune’s are named after astronomers associated with the planet, specifically Galle, Le Verrier, Lassell, Arago and Adams. Adams is the one with the wider arcs, which are named Liberté, Egalité, Fraternité and Courage. Egalité is split into 1 and 2. Three small moons orbit between the rings, and there’s another ring associated with the moon Despina. In a way it’s quite nice that there’s a French theme to the naming contrasted with the English theme for Hamlet, but I don’t know if it’s deliberate. One really surprising thing about them is that the supposèd “discovery” was actually an occultation by the moon Larissa, so although they were correct about them being rings, they were correct by chance and misinterpretation of an unusual astronomical event. Neptune is a harder target for ring detection than Hamlet, although that is itself not easy, because it moves so slowly against the background with its 165-year orbit. The rings are, like the other ice giant’s, very dark and of course even dimmer due to the greater distance from the Sun. There’s a big contrast in the widths, with the three inner rings being only about a hundred kilometres wide (i.e. their height) and the others being several thousand, which is unlike Hamlet’s much thinner ones. An image of them with the contrast turned up to show details of the structure looks like this:

It’s really come to something when a planet invisible to the naked human eye is made so bright that its glare almost bleaches out the view of its even dimmer rings. This is a ten-minute exposure made by Voyager 2, which was right there, and still the rings are hard to see without that kind of technique. Whether the average human eye could see them is another question, as ours are very good at adjusting to low-light conditions. It still isn’t that low though, at least compared to bright moonlight, but I fear I’m repeating myself. In fact, all the conditions that apply to sunlight on Pluto also apply to it on Neptune because their orbits overlap distance-wise (they don’t literally). Hence the Sun at Neptune’s distance is just a star. The minimum visible object to someone with good vision is one minute of arc across. After that, it’s visible if it’s luminous but not as an actual shape. This is equivalent to a hair’s breadth viewed from twenty-five centimetres away. From Earth, the Sun appears as a disc thirty times that diameter and is therefore very obviously a ball of light. Neptune, however, is thirty times as far away and the Sun could therefore not be seen as anything more than a star, which is effectively a point source of light. This is, however, quite misleading as it’s still many thousand times as bright as any other star in the sky, and might therefore not appear as a point due to its glare. Lighting conditions on Pluto have been likened to those on Earth after a sunny day shortly after sunset, so the same kind of thing can be expected on Neptune and its moons. In other words, you’d probably hardly notice it at all after a while and it would look like broad daylight, except that the actual illumination is only a thousandth that of the Sun’s here. Looking at it from the other end of the telescope, as it were, Neptune is the only planet in the system, taking Pluto as a non-planet, which is never bright enough to be seen. Its maximum brightness is something like four times dimmer than it would need to be to become visible. Of course there will, as with other celestial bodies, be other species who can see it and in fact Galileo saw it, through a telescope of course, but didn’t notice it was a planet. Likewise, it was reported that it had rings shortly after it was discovered but in this case it was probably an illusion.

Neptune has a rather odd array of satellites. At one point it was thought that Triton might be the largest in the Solar System, and as I mentioned above it orbits backwards compared to most other moons. Nereid has a very eccentric orbit. Up until the 1980s, these were the only two moons known, but Voyager 2 surprisingly discovered a moon, now called Proteus, which is actually larger than Nereid, making it the largest object discovered by the Voyager probes. Due to the mistake leading to the accidentally correct conclusion that the planet has rings, the moon Larissa was also detected in 1981 but it wasn’t realised that this had happened, rather like Galileo and Neptune itself. Voyager 2 found another five, including Proteus, and a further six were discovered this century. Neptune also holds the record for having the most distant moon and the longest time taken for that moon to orbit, Psamathe, which is fifty million kilometres from it and has a period of almost twenty-five years. There are various interesting things going on with Neptune’s moons but that can wait until my next post.

Probably the most prominent appearance of Neptune in science fiction is in Olaf Stapledon’s ‘Last And First Men’. Published in 1930, the science is well out of date, although the description of a yolk in an enormous egg is valid. In this account, our distant descendants are living on Venus an æon hence when they observe a mass of gas on a collision course with the Sun which will cause the Solar System to be disruptd and the Sun to become what we would probably call a red giant the size of the orbit of Mercury. Humanity decides, though not en masse, to escape to Neptune, where it has to contend with enormous gravity and pressure, and first a very cold climate followed by a very hot one. Humans cease to be intelligent and take four hundred million years to evolve into a sentient form again. This is partly because their lifespan is much longer, as most species live at least one Neptunian year. They ultimately become superhuman beings who notably have ninety-six genders and a life expectancy of a quarter of a million years. I find this section of the novel, if that’s an accurate description, to be a particularly satisfying example of speculative evolution, although one which has been left standing by scientific discoveries about the planets involved.

That’s probably a fairly adequate introduction to Neptune. Next time: Triton.

Into The Gap

I’m not quite sure how this post is going to go. It’s not going to be the same as the others. Then again, neither was the one about the name of the seventh planet from the Sun. It is, however, somewhat similar to the one about the space between the Sun and Mercury.

Up until now, I’ve mainly posted about the planets, moons and asteroids of the Solar System in one way or another, but one of the most impressive things about the system is not so much the worlds it contains as the enormity of its scale, which is of course itself dwarfed by interstellar space. In a way, the Solar System is a rather irregularly-shaped space centred on the Sun with a radius of at least a light year in every direction. Beyond those points, the gravity of other bodies, usually stars, becomes more significant than that of the Sun. This is a significant feature of the system because out there in the darkness lurk countless bodies, perhaps future comets, and although the distances between them are huge, it can’t be said that this space is entirely empty. However, that isn’t what most people think of as the Solar System, and that’s what I want to consider here.

Most people probably think of this thing as the Sun plus eight or nine planets with the occasional comet. Whereas popular perception may not be the best way to go with science, the system isn’t just about science. The Apollo astronauts walking on the nearest celestial body, for example, weren’t merely “science”, and the discoveries about the Martian atmosphere which helped end the Cold War were very significant for all of us. Looking at Saturn through a telescope for the first time isn’t about science either, but awe and a sense of beauty. Nonetheless, science comes into this.

Saturn is something over ten times Earth’s distance from the Sun. Its orbit circumscribed the known Universe for thousands of years. Within that ellipse, with a little latitude either side of its orbital plane, is a rather busy and light community of stars, asteroids and moons, the largest of which have been visited more than once by space probes. In fact, the largest object never to have been subject to a mission at all in this region is the asteroid Hygeia, with a diameter of 450 kilometres. Outside this region are the seventh and eighth planets plus Pluto and the distance between Neptune and the next planet in is a minimum of almost eleven times that between Earth and the Sun. In other words, the entire distance between the Sun and Saturn is smaller than the width of this gap. It’s also fair, if technically inaccurate, to consider the orbit of Neptune as the true border of the Solar System. It isn’t of course, but we can think of it in that way if the system is considered the set of official planets orbiting the Sun.

Voyager 2 took eight years to travel from Earth to Uranus (sigh). It then took only three more years to cross this enormous gulf, slowing as it went. This is a bit of a distortion because there’s a huge gap between the sixth and seventh planets too, about the same as that between Earth and Saturn at their closest to each other, so in other words a comparable distance to the next gap. However, beyond Saturn lie most of the centaurs, the relatively huge satellite system of that planet and also its magnetic field, and Saturn is also large and able to exert a considerable gravitational influence on the region. This gap is different. The two planets marking its edges are smaller and less massive and in fact roughly the same size. This means there will be a moving point halfway between them where their gravity is balanced, at around two dozen AU from the Sun but varying and sometimes being dominated by the forces of other bodies. The situation is actually quite like that between Venus and Earth due to their similar masses but on a much larger scale. Although the gravitational forces involved are much lower, there’s also a lot less to perturb these forces in such an uncluttered region.

Many objects orbit on either side of this gap. The centaurs are substantially found further towards the Sun and the realm of the Kuiper Belt is beyond Neptune. This raises a couple of complementary questions. One is whether the gap contains such objects and the other is, if it doesn’t, why? Clearly the further out from the Sun one goes, the less stuff there is. However, in this case there’s a difference between the objects on either side, with small, comet-like objects within Hamlet’s orbit and often relatively large, planet-like objects beyond Neptune’s. What, then, is present between them, if anything?

One very definite and obvious object spending time in the gap is of course Pluto. It was there between 1979 and 1999 CE. Pluto does not, however, cross Neptune’s orbit, at least most of the time. It’s inclined at seventeen degrees to the ecliptic compared to Neptune’s one degree and four dozen minutes. Like all planets, however, both Pluto’s and Neptune’s orbits gradually “spirograph” around the Sun over a long period of time, and therefore theoretically they could collide at some point. They never have, or Pluto would no longer exist, or perhaps it’d be a moon of Neptune like Triton is, along with its own companions. Pluto ventures twenty-three million kilometres closer to the Sun than Neptune does, although that doesn’t mean it ever gets as close as that to Neptune due to the angle of the orbit. In fact, even at their closest approach the two can be as far apart as Earth and Saturn, which gives a sense of the scale involved at that distance. Pluto’s tilt also doesn’t really need an explanation. It’s simply that the gravitational influence of the Sun is weaker out there, and Pluto is not very massive and therefore has less momentum than the likes of Neptune.

It’s been calculated that the region from twenty-four to twenty-seven AU from the Sun is a haven for objects with stable orbits over the age of the Solar System to date, so there are some reasons for supposing there will be something there. This is actually quite exceptional and doesn’t apply, for instance, to centaurs, whose orbits are unstable over a period of a few million years. An object around that distance in a roughly circular orbit will never be captured by a planet, dragged into the inner system like a comet or ejected far out of it. In fact, this is the largest region where there are potentially stable orbits all the way from the Sun to Pluto’s aphelion. This belt is divided into two particularly stable regions around 24.6 and 25.6 AU. These calculations also predict that there are around three hundred objects at least fifty kilometres in diameter in this belt, which can be compared to the Kuiper Belt, some of whose occupants are much larger than that. The reason they haven’t been detected is likely due to their darkness and the dimness of solar illumination at that distance. They would be hard to spot. If they do turn out not to be there, it suggests that an event such as a planet shifting its position through that region has cleared them from it. That planet might actually be Neptune because it’s in the wrong place. Neptune alone among the planets does not obey Bode’s Law. Another possibility, and I say this as a naïve amateur, since to my knowledge this has never been suggested, is that this apparently clear space is the result of a “mini-Neptune” moving through it before being ejected from the system. The most common type of planet detected orbiting other suns is a planet about midway between Earth and Neptune in mass, so maybe this is where it used to be. It’s unlikely because it would again violate the Titius-Bode Series.

Suppose, then, that a typical cis Neptunian object has a diameter of fifty kilometres and has a roughly circular orbit near the ecliptic plane at a mean distance of 25.6 AU. What features would it be likely to have? Well, it would take 129 years to orbit the Sun, which at that distance would be six hundred times dimmer than from Earth. It would also have a fairly dark reddish surface, moderately cratered, and probably hasn’t been geologically active for a very long time if at all. Surface temperature would be around -200°C and it would be composed of an undifferentiated mixture of ice and rock. In fact, it would probably very closely resemble some of the outer moons of the two ice giants and that may be where those came from in the first place.

Another thing about this region is that the centaurs and Kuiper Belt each impinge on it, from opposite sides. There are a considerable number of trans-Uranian centaurs. One of these sounds very much like the predicted type of object: 2005RL₄₃. This is 24.6 AU from the Sun, has negligible eccentricity and has a diameter of 143 kilometres. Another is Nessus, although that has a very elliptical orbit. On the other side, clearly at least one plutino moves into the gap so the question arises of whether there are any others. The definition of a plutino is that it orbits twice for three orbits of Neptune, which is what Pluto itself does. This does put their mean orbit at a distance of 39 AU, about the same as Pluto’s and also in accordance with the Titius-Bode series, but there’s no reason a body beyond Neptune wouldn’t be within its orbit for part of its year, and this would put them in the gap. I don’t want to spend too long on this because at some point I want to talk about Kuiper Belt objects in their own right, but it would be remiss of me not to mention them here too. Some of them dip into the stable region at their perihelia. A few of them even approach the Sun more closely than Saturn and there’s one which not only does this but also recedes to a maximum of more than thrice Pluto’s distance. Plutinos are not the only class of trans-Neptunian object. Cubewanos stay beyond it and twotinos orbit once for every two orbits of Neptune. There are two known twotinos whose perihelia are within Neptune’s orbit, just barely. In other words, their orbits are less eccentric than those of the plutinos.

There are some comets whose aphelia are lower than Neptune’s. Each gas giant has an associated cometary family, whose aphelia are close to those of the planets. Jupiter’s is largest, followed by Neptune’s. That of the seventh planet is particularly small. There isn’t too much more to say about it than that, except that as well as these two families, other comets move through this region on their way in and out of the inner Solar System. The gas giants attract and steer comets into these orbits, and this happens with the two ice giants. Neptune is closest to the Oort cloud, so it’s particularly significant in this respect.

If the orbits of the planets marking the edges of the gap are projected onto the ecliptic, the area of this region is just over 1500 square AU, which is almost five hundred times the area of Earth’s orbit and 175 times the area of the inner system. Space has more than two dimensions of course, and the bodies occupying and defining this region don’t orbit in the same plane, particularly the moons of Hamlet. Features characterising it are quietness, coldness and dimness.

I just thought I should mention it because it’s easy to ignore the space between things.

The Globe Theatre In Space

Yes, I know I’m supposed to be alternating.

I’m not sure how much to make of the idiosyncratic naming scheme for the moons of the seventh planet from the Sun. As a fan of language and word play, they appeal more to me than they perhaps should if I’m just going to be talking about them in a scientific way, but the fact is, there’s the Universe and there’s the person observing the Universe, and you can’t entirely step outside yourself. The rest of the Universe is, in a sense, your mind reaching out to it and placing it within your own private world. It’s part of you. That said, science tries hard to be objective. However, it’s significant to many of us that twelve Americans walked on Cynthia and that people do romantic things “by the light of the silvery Moon”. Cynthia is culturally significant to us.

With regard to the twenty-seven known moons of the planet I’ve been calling Hamlet, it might be a little hard to imagine how such a small system so far away from us could have any consequences for us Earthians. They don’t figure prominently even in the realms of science fiction and astronomy. If we had sent more than one probe to the system, maybe it would be more significant to us all. If it turned out to be the only other abode of life in the system, it would be considered hugely important. There is in fact at least one aspect to the planet which makes it relevant to life here. There is only a weak internal heat source and the Sun makes little contribution to its temperature, leading to computer models of the atmosphere being dominated by the Coriolis Effect. Due to the abstraction of the model from observed conditions, which of course confirm its accuracy, this constitutes yet another refutation of the hypothesis that Earth is flat, because of how the effect operates in our own atmosphere and attempts by flat Earthers to explain this in terms of solar heating (and perhaps lunar cooling!). Even this, though, is something of a niche explanation.

The moons concerned, taken together, don’t add up to much, which is why I’m dealing with them all in one go. Their total mass is less than half that of Titan, and also of Neptune’s giant moon Triton, but this isn’t the same as saying they’re small for two reasons. Firstly, Titan itself is 96% of the mass of everything orbiting Saturn including the rings, so the seventh planet’s moons are actually bigger en masse than all of Saturn’s except for Titan. Secondly, volume, surface area and diameter are counter-intuitive. Our own moon has only 1/81 Earth’s mass but has a diameter a quarter of our planet’s. By the time you get this far out from the Sun, even many compounds gaseous on Earth are frozen solid. Umbriel is probably the warmest moon, because it’s dark and absorbs more light, and has a maximum temperature of -188°C, barely warmer than the boiling point of air. One consequence of this is that the densities of the moons are very low, which means they’re larger than their masses suggest. It’s also interesting to compare the situation here with that in Neptune’s vicinity.

I’m going to reiterate this yet again in case you’re coming across this post without having read any of the others: the moons of the seventh planet don’t take their names from any mythological tradition, but from works of literature, mainly Shakespeare’s plays. I find this refreshing but there is an element of cultural imperialism to this. Then again, the same is true of the dominant Greco-Roman tradition for the other planets, moons and asteroids in the system, but what’s done is done I suppose. There were two widely separated phases of discovery, which is also true to an extent of the other gas giants but in the cases of Jupiter and Saturn the rate of discovery is rather different. Jupiter’s Galilean moons were all discovered in 1610 CE, then nine moons were found between 1892 and 1975, followed by three via the Voyager probes and a spate of discoveries from 2000 on. Saturn’s show a more regular distribution between the seventeenth and nineteenth centuries, a rush associated with the Voyager missions and a further sequence of discoveries from 2000s on as with Jupiter’s. My experience of Hamlet’s moons is that five were known when I was a child, and because one’s childhood experience is just how things are, and one hasn’t yet gotten used to change, that was just how things were. I wasn’t aware of the peculiar naming scheme because at the time they seemed just to be kind of Latinate, for instance Ariel and Miranda, although one is much more likely to come across a human Miranda in everyday life than, say, a Phœbe, and way more likely than meeting someone called Ganymede. The first four were discovered in pairs in the eighteenth and nineteenth centuries, then Miranda in 1948, then we had to wait until Voyager for any more discoveries. After that, Caliban and Sycorax were found in the ’90s, Perdita was discovered using old Voyager data and the rest come from between 1999 and 2003. Since then, no more discoveries have been made but this might be because Hamlet is a neglected planet compared to the others, so maybe nobody’s looking. It is also very dim and distant, so it might be that.

Titania is the largest. This is quite possibly the poorest decision ever in naming a moon. Titan was already known by the time it was discovered and there are different ways of pronouncing it. And how do you refer to something to do with Titania without people thinking you’re talking about Titan? However, we can talk about the place. It’s the largest and most massive of the moons in a system which isn’t particularly large or massive. Here it is:

That slight blurring is probable due to the impossibility of correcting entirely for Voyager 2’s motion blur. About forty percent of its surface has been seen. Like the other moons, Titania doesn’t orbit near the plane of the Solar System due to its planet rotating on its side, meaning that that illuminated surface in the picture remains in daylight for decades at a time, just as the other side stays in night. This means that one pole is somewhere near the middle of the lit portion of that image, in this case the south, because like all such images of the moons, this was captured in 1986. All the large moons are about half rock and half ice, so they’re actually denser than many of Saturn’s, and Titania is both the largest and densest of all of them. All the moons also have largely grey surfaces, Umbriel being darker than the others, hence its name. Titania is half Cynthia’s width and has icy and dry ice patches on its surface. It’s considered likely that it’s differentiated into distinct layers with a rocky core and icy outer layers. There may be a little liquid water inside at some level. There could also be a very thin non-collisional atmosphere of carbon dioxide.

Oberon was discovered with Titania and is slightly smaller, orbiting outside Titania’s path. It’s more heavily cratered. Both are at comparable distances from their planet as Cynthia from Earth. For some time after the pair was discovered, it was thought that there were six moons overall but after many years the others came to be considered spurious, although of course there are other moons. A significant difference between it and Titania is that the latter orbits entirely within the magnetosphere whereas Oberon passes in and out of it. Again, only forty percent of the surface has been mapped. It’s also the outermost large moon. Oberon’s features are named as follows:

The surface has a sheen to it and is slightly red except where newer craters have yet to acquire that: those are slightly blue. This reddening is due to space weathering, where electrically charged particles hit the surface. Unlike all the other large moons, the trailing hemisphere has more water ice than the trailing one. It’s almost exactly the same size as Rhea, which makes me wonder if there’s a peak in moon sizes at about this diameter across the Universe as it’s also quite close to Titania in size. There are apparent rift valleys, such as Mommur Chasma. In the distant past, when the moon was young, processes within it had an influence, namely its slight expansion by about half a percent of its diameter. Mommur Chasma is apparently named after the original French version of the tale of Oberon’s home, «Huon de Bordeaux».

Miranda and Umbriel are probably the most distinctive of the large moons. “Miranda” the word is a gerund meaning “worth seeing”, hence the “-anda” names Amanda – “worthy of love” and Miranda. Samuel Johnson once said of the Giant’s Causeway that it was “worth seeing, but not worth going to see”. Well, Miranda seems to fall into the same category. It is indeed worth seeing but given that only one spacecraft has ever been there, possibly not worth going to see. However, it’s still remarkable. Here it is:

As you can see, it looks rather rough. It has a diameter of 370 kilometres and is therefore on the lower edge of worlds whose gravity is able to smooth them into an approximate sphere. At some point in the past, it was hit by something and shattered into small pieces which then all fell back together haphazardly. There are enormous cliffs all over the moon, including the highest cliff in the System, Verona. Twenty kilometres high, if an object falls off Verona cliff it would take ten minutes to fall to its foot. Although it’s tempting to believe that these cliffs are the result of the shattering, they’re more likely to be due to the same kind of expansion as Oberon’s chasms. The number of craters suggests Miranda was only formed during the Mesozoic, or at least that whatever happened to it took place then.

Umbriel is the only major moon not at least ambiguously named after a Shakespeare character. Instead, the name is taken from Alexander Pope’s ‘The Rape Of The Lock’, where it refers to a “dusky melancholy Spright”, also referred to as a gnome. Clearly the name is related to the Italian and Latin “umbra” – shadow. As well as being particularly dark, Umbriel has a crater outlined in bright white material where a pole would’ve been if it orbited normally, but it so happens not to be situated there because of its primary’s odd axial tilt:

The mere fact that the light ring is at the top of this picture shouldn’t be taken to indicate that it’s at any kind of pole, because the moon rolls round as it orbits in a manner typical of such bodies, but its orientation here makes it look like a polar feature. Its name is Wunda and the feature is ten kilometres wide. Its origin is unknown. The surface is generally dark bluish, although that’s a relative way of describing it along the lines of “black” often being tinged with a cast of a particular hue rather than it being pure black. However, it also seems odd to me because most dark objects in the outer system are red-tinged rather than blue, suggesting that it isn’t the usual tholins that are coating the surface. Nothing other than craters are known on the surface unless you count the ring.

Ariel is the other major moon with an ambiguous name, as it could be named after either Ariel from Shakespeare or Ariel from Pope. Its mass is about the same as all the water on Earth’s surface. It’s somewhat bigger than Miranda and slightly larger than Ceres. It’s half ice and half rock, and despite its name has no washing powder on its surface. That comment isn’t quite as flippant as it sounds because other bodies in the Solar System do have washing soda in and on them, including Ceres.

Not the same thing

What the heck is it about this planet and its system which leads to it having such peculiar names‽

Right, so Ariel is the second closest major moon to its planet. It’s also the brightest per area at around four times as bright as Cynthia, although being twenty times as far from the Sun it only has a four hundredth of the sunlight falling on each square metre in the first place and is well under half the size. Its surface is more varied than the likes of Umbriel, as far as has been seen anyway, with canyons, ridges, craters and plains all present. The chasms are often bowed in the middle rather than flat or tapering, and seem to result from freezing water and ammonia altering the dimensions of the moon. Chasms often become ridges, suggesting that they are a similar response to the freezing of liquids, so the moon’s surface could be seen as a mixture of the wrinkly deflating balloon and the cracks of an expanding soufflé (but without the bubbles). The plains are probably similar to lunar maria, in this case involving the eruption of a thick liquid, possibly a mixture of ammonia and water. There are no large craters, suggesting that the surface is younger than the Late Heavy Bombardment period early in the system’s history. The largest crater is the 78 kilometre-wide Yangoor. Ariel has similarities with Saturn’s Dione.

Those, then, are all the large moons. To summarise that bit of the system, they are in order Miranda, Ariel, Umbriel, Titania and Oberon. Their spacing corresponds to a law similar to the Titius-Bode Series relating to the spacing of the planets, if that is indeed valid. Mary Blagg’s 1913 generalisation of Bode’s Law yielded the formula A(1.7275)ⁿ(B+f(α+nβ)), where A for this system was 2.98 and B 0.0805. Hence there seems to be something orbital resonance-related going on here. Some of them were probably warmer in the past due to having less circular orbits and so more vigorous tides.

I want to mention a slight personal peculiarity at this point. As a small child I used to delight in memorising the names of the moons of the outer planets. This led to the oddness of Jupiter’s moons having their names changed to my considerable confusion in the late ’70s. In the case of “Hamlet”, the seventh planet, the planet whose name one dare not speak, the list was rather short and didn’t really stick in my memory, but oddly it had an extra member according to my unreliable recollection: Belinda. I didn’t think much of this because the subject of those moons rarely or never arose until 1986, and even then it wasn’t all that, partly due to the Challenger disaster. Belinda is a small moon orbiting below Miranda which wasn’t discovered until 1986. I had no knowledge of ‘The Rape Of The Lock’ at this time, so I can’t account for the fact that for well over a decade I thought there was a moon called Belinda when it didn’t even get named until after the Voyager 2 mission. This seems to be rather akin to a Mandela Effect, such as the placement of single releases in my memory being several years different than in reality. For what it’s worth, Belinda is an elongated moon 128 kilometres long by sixty-four kilometres wide and extremely dark, and it may collide with other moons in a hundred million years or so, so it could be a future ring. There are thirteen known moons within Miranda’s orbit and many of them are elongated, although I personally wonder if that’s the reality or whether it’s motion blur. Presumably that’s been taken into account though. These cis Mirandan moons are known as the “Portia Group” and are named Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, (the second largest, at 156 kilometres maximum diameter), Rosalind, Cupid, Belinda, Perdita, Puck and Mab. Puck is the largest, with a diameter of 162 kilometres and was the first discovery after the larger moons, in 1985, by Voyager 2 shortly before it began the main part of its mission. It’s heavily cratered, dark and has water ice on its surface. Because it was the first moon to be discovered, there was time to program the probe to get more information on it than the other small moons. Three of its craters are named: Butz, Lob and Bogle, named after impish spirits in European mythologies.

Then there are the nine known outer moons, which are trans Oberonian: Francisco, Caliban, Stephano, Trinculo, Sycorax, Margaret, Prospero, Setebos and Ferdinand. Sycorax is the largest of these at 157 kilometres diameter. It’s more than twenty times further out than Oberon and is light red in colour. It has its own rotation period of seven hours, not locked to the planet and takes three and a half years to orbit. It averages twelve million kilometres from Hamlet. All of the outer moons orbit backwards with respect to the planet, which itself technically rotates in the opposite direction to all other official planets except Venus. The orbits are not in the equatorial plane. The outermost moon is Ferdinand, orbiting on average twenty million kilometres from the planet and taking almost eight years to do so. Margaret is unique among this group in orbiting in the same direction as the large moons.

When the large moons were first discovered they were numbered in order of their discovery. This was then changed to the order of their distance from the primary because of course they’d change the system because it’s “Hamlet” isn’t it? Hence there are two different numbering systems.

It isn’t that the moons are less distinctive or interesting than those of Jupiter and Saturn, although they may in fact be, so much that little is known about them. The larger ones certainly seem to be more similar to each other than those of the two largest gas giants and there isn’t as much interaction between them. They are also rather unlike the moons of Neptune, which include a major anomalous member. The general impression they give is of a system of remarkably unremarkable moons of average dimensions, although in a way this is surprising considering that they all effectively have days lasting seven dozen years.

I’m not sure what to do next. I will probably more on to the rather similar Neptune, but there might be something interesting going on between the orbits of the seventh and eighth planets so I might also consider that.

Planet Hamlet

Look here for an explanation of the post title. At least for this post I shall be calling this planet Hamlet rather than the silly name. So far as I know, nobody has ever called it that before and it may not function well as a viable official name, although I think it would. Although there may be issues of cultural imperialism, the character as portrayed in the play in question is in a sense global property. On a different note, it has an even lower population than a hamlet.

Hamlet used to fascinate me inordinately as a child, probably for two reasons. One is that it’s blue. In fact, Neptune is if anything bluer, the image above being false colour, but James Muirden the astronomer commented in his book that he definitely saw it as having a blue tinge even though everyone else seemed to see it as green. The border between green and blue seems to be more disputed than most colour differences, and it’s worth remembering that colour terms in other languages often vary, and also tend to occur in a particular order. I presume that Japanese calls the colour in question “青”, as does Mandarin (kind of). The other reason is that for whatever reason, Hamlet is the most obscure planet, being mainly used as the butt of jokes because of its name, which makes it intriguing and a target for the imagination. Hamlet is also only a little denser than water, and at the time of the 1930s (CE) encyclopædia I was getting my info from, its density seems to have been estimated as the same as water, suggesting to astronomers at the time that the planet was a globe of liquid. In 1977, I wrote a story called ‘A Holiday On Uranus’ about exactly that, set in 2177. I remember it fairly vaguely, but in it Hamlet was inhabited by intelligent fish-like beings living in its vast ocean and there was a security scanner used at the spaceport which used terahertz radiation to reveal the surface of the body in clothed people, which was eventually invented for real. Travel to the planet was at near the speed of light. I also imagined slavery in the Saturnian system and cruel and oppressive measures being taken to modify the bodies of Saturnians to make it impossible for them to rebel in an analogy to the Atlantic slave trade. I still have it somewhere I think.

At that time it was still possible to project one’s imagination onto the outer Solar System in such a way, although my view was clearly influenced by the fact that most of what I’d read about Hamlet had been written in the ’30s. Also, in one of those odd random associations one gets as a child, Bing Crosby’s ‘Little Sir Echo’, about a personified echo who was “ever so far away”, always used to make me think of someone living there, and I even went so far as to calculate how long it would take sound to travel the distance from Earth to the planet and back, which is around five and a half centuries. I also imagined a steam locomotive travelling there, which would probably take about a millennium, though that’s a guess. It strikes me that all my imaginings about Hamlet were extremely outdated even for the time I was making them.

Back in Stapledon’s day, and he was chiefly active in the 1930s as far as popular fiction was concerned, the giant planets weren’t considered to be gas giants, but extremely large rocky planets with thick and deep atmospheres. Consequently he was able to imagine Neptune in particular, and also to a limited degree Hamlet, as planets inhabited both by native life and the descendants of life from Earth, and given the increased radiation from the Sun æons in our future, Hamlet has agriculture at its poles, the equator being too hot, suggesting that at that point its peculiar rotation had yet to be discovered.

This brings me to the first real point about the planet: it “rolls around” on its side. Hamlet does not rotate “upright” like most other planets. It doesn’t even rotate at a somewhat tilted angle. Instead, each pole spends a season of the seven dozen-year long orbit pointing towards and at another time away from the Sun, as its axial tilt is 98°. This means that for most of the surface, with the exception of the equatorial region, there are forty-two years of daylight followed by another forty-two years of night. Hamlet does, however, rotate properly every seventeen hours, so at the equator it would have a normalish day with sunrise and sunset. This zone is about fourteen thousand kilometres wide. If it was much closer to the Sun, this peculiar arrangement would lead to very extreme seasons, but Hamlet is actually colder than the next planet out, Neptune, at -224°C. It has the coldest average temperature of any of the planets in the system. This anomalous situation is thought to be caused by the same incident which tilted it so extremely. It’s believed that a major impact or close encounter between a massive object and Hamlet knocked it onto its side and stirred up its atmosphere to the extent that the warmer layers nearer the centre of the planet, where the temperature is about 5000°C, ended up circulating towards the cloud tops and radiating the heat which in other gas giants is insulated from space by thousands of kilometres of not very conductive fluid. It might be thought that the reason is that half the planet is in darkness for forty-two years at a time, but this is not in fact the reason. Hamlet is so far out that it doesn’t really make as much difference to the temperature, and like many outer worlds the internal heat is a major contributor to the climate and weather. However, Hamlet is smaller than the two inner gas giants and has no significant tidal forces to generate heat, so it would in any case have a much cooler interior even without the incident which stirred it up.

When he discovered the planet, William Herschel thought it was probably a comet. It’s remarkable in being the first planet to be consciously discovered in historical times. There is a sense in which Venus was discovered when it was realised that the Morning and Evening Star were identical in the thirteenth century, which also led to it being given that name because the Morning Star was dedicated to the goddess, but an entirely new planet had never been discovered before. Remarkably, Herschel lived to the age of eighty-four, which is the same length as Hamlet’s year. Asteroids began to be discovered about twenty years later. The planet often seems to be passed over. For instance, there are relatively few works of SF which feature it. One exception is Fritz Leiber’s ‘Snowbank Orbit’, a 1962 short story in which the spaceship Prospero ejected from the inner system by an explosion in a battle attempts a slingshot orbit around Hamlet to bring it back inward. This was before such a manœuvre had been attempted for real as far as I know, but is now common, though not round the planet in question. Leiber tends to focus on Shakespeare, so his inclusion of Hamlet in that tale is probably due to its own naming theme. I haven’t read it all, but suspect that the planet only really participates in the plot as a distant “roundabout” rather than a planet in its own right. To be fair, so little was known about the place back then that it might not have had much opportunity to be anything else, although it’s all about imagination and Leiber was substantially a sword and sorcery author as much as an SF one. Cecelia Holland’s ‘Floating Worlds’ novel does have it as a proper location though. I actually owned that book for decades but never got around to reading it before I ended up giving it away, so I can’t enlighten you on its content.

The key concept here, then, seems to be that Hamlet tends to be ignored to a much greater extent than other planets, except for the obvious occasional puerile comment. Is this fair? Is it just that the silly name puts people off taking it seriously, or is there something about it, or perhaps all the other planets, which lends itself to being ignored? Is it the Basingstoke of the Solar System? Come to think of it, is Basingstoke really that boring? Am I being unfair? All that said, Hamlet as a planet, as opposed to our relationship with it, is indeed unusual because of the fact that it orbits on its side, if for no other reason. It’s also the first planet to be found with rings after Saturn, within my lifetime in fact, and its rings are notably different to Saturn’s, being darker, thinner and more widely spaced. Its moons are, uniquely in the Solar System, not marked by any outstanding features. Neptune has the kudos of being the outermost planet if Pluto isn’t counted as one, and for twenty years at a time Neptune really is the outermost due to Pluto’s peculiar orbit. Neptune also has unusual moons and the fastest winds in the system, but I’ll deal with all that when I come to it.

It is, however, worth comparing the two worlds, as they’re probably the two most similar planets in the Solar System. I’ve kind of been here before. Both are roughly the same size, very cold, the same density and have similar day lengths. They also have similar colours and compositions, and their size and density dictate that their cloud top gravity is similar. Although Hamlet is the colder, the difference is only about ten degrees, bearing in mind, however, that ten degrees is a bigger difference at such a low temperature than it is at room temperature and more like a difference of thirty degrees for us.

Here’s the picture I posted last time:

This is Hamlet as it looked to Voyager when it got there in ’86. The equinox occurred in 2007 so this is something like twenty years off from that, a quarter of a “year” or so away from that point. It’s exceedingly featureless and fuzzy looking, unlike the much clearer and more vivid Neptune:

It’s possible that the haze in the atmosphere of the closer planet is seasonal, but this rather uninspiring view is enough to make one understand why it tends to be ignored. After all, just imagine if a space probe costing millions had been dispatched all the way to the place and it had come up with nothing but for the greenish cueball image shown above. Fortunately, Voyager visited all four gas giants and is to date the only spacecraft ever to have visited either Hamlet or Neptune. It took four and a half years to travel the distance from Saturn to Hamlet and at the time it got there, January 1986, the planet was invisible to the naked eye. Hamlet dips in and out of visibility because of its distance and orientation, but is bright enough to be visible as a faint “star” some of the time to people with good eyesight who know where to look. In order to get a good look at Titan, Voyager 1 had manœuvred itself out of the plane of the Solar System and visited no planets after Saturn in late 1980, but Voyager 2 went on to cover Hamlet and Neptune. This means, of course, that the planet didn’t get as much attention as the previous two in any case. There were also imaging challenges. The rings are as dark as coal and the moons are not only dark but also dimly-lit compared to Jupiter’s and Saturn’s. Moreover, the velocity with which Voyager 2 moved through the system marred many of the images with motion blur. This brings up an important issue often raised by conspiracy theorists about NASA. Images taken by space probes are, as far as I know, always processed from the raw form in which they’re received, for this kind of reason. There may be too much or too little contrast, and in this case the problem was that the blur had to be filtered out. I have little idea regarding how this was done, as I would’ve thought that blurring would mean that some features would have obliterated others completely owing to brightness, but maybe not. I do know it seems impossible to get rid of a different kind of blur with processing in that way, namely when things are out of focus, because otherwise an out of focus image could be drawn which would appear to be in focus to someone with myopia, and that doesn’t happen, I’m guessing because of entropy. However, motion blur is not the same thing. Techniques of processing the blur have also improved since 1986, so it’s been possible to extract new information from the data received at the time. In the case of Hamlet I’m tempted to say that it hardly matters because so little detail is apparent, due not to motion blur but the basic appearance of the planet itself.

Another aspect of Hamlet’s appearance is that for human eyes the green-blue colour tends to dominate and make details hard to see. This is similar to the way a clear daytime sky on Earth, so to speak, looks bluer than it really is to many people. This sounds like nonsense, but I have to interject a personal note here that I don’t actually see the sky just as blue, and this is an issue which has come up repeatedly and I haven’t been able to resolve satisfactorily. When I look at a cloudless blue sky in broad daylight, I see large purple “splotches” all over it. These are not directly linked to my vision because they stay in the same parts of the sky when I look around, so it isn’t a question of glare creating an optical illusion due to the blood in my retinæ. It may be connected that in fact the Rayleigh scattering responsible for the bluish colour of the sky isn’t confined to blue wavelengths but actually affects indigo and violet light even more, and I suspect that what I’m seeing is uneven scattering of these higher frequencies. I don’t know why I would notice this more than other people. I wouldn’t go so far as to say that I see the sky as purple or indigo, but it definitely doesn’t look merely blue to me, and for some reason nobody else has ever mentioned this, so I presume they don’t or can’t see it. Nonetheless, if the human eye were equally sensitive to all wavelengths of visible light, the sunlit sky wouldn’t look blue to anyone but more indigo.

I’ve never seen Hamlet with a telescope or anything else, but only via images processed imperfectly for human colour vision. Through violet, orange and red filters, the globe is banded in the same way as Jupiter and Saturn are, though more subtly. The green and blue colour of the atmosphere, however, drowns this out to the unaided human eye. I’ve previously mentioned conspiracy theorists in connection with the question of NASA image processing. Flat Earthers would have the same problem explaining models of Hamlet’s atmosphere as Titan’s, because of the dominance of the Coriolis Effect. Hamlet is very cold indeed, unlike Jupiter and Saturn has only a weak internal heat source, and unlike all other planets in this system orbits on its side. This means that models of its atmosphere correctly show the movements of clouds in a counterclockwise direction dominated by the Coriolis Effect. Note also that these models do not depend on the actual existence of the planet itself, since they’re merely an extrapolation of what happens in a fluid body of Hamlet’s character. The movements are dominated by the movements of the planet itself and not by heat from inside or outside, in spite of the fact that entire hemispheres are daylit for forty-two years at once while their antipodes are nocturnal for the same period, and it might be thought there would be a big temperature difference driving the winds, but there isn’t. This is difficult for flat Earthers to explain because of the rotation of weather systems in our own atmosphere being clockwise on one side of the Equator and counterclockwise on the other.

Hamlet has a number of unusual features which are difficult to explain simply. It rotates on its side, the magnetic field is neither oriented towards the poles or particularly away from them and originates from a location about a third out from the planet’s centre. It’s also colder than expected, and the moons are unusual as well. The most popular explanation is that a roughly Earth-sized body collided with the planet and still has much of its material within it, knocking Hamlet off its axis, changing its composition and causing the formation of carbon monoxide from some of the methane, in other words burning the atmosphere via incomplete combustion due to low oxygen level. Although this is also used to explain the strange magnetic field, I don’t know the connection. Maybe no-one does. This peculiarity also means that unlike any other known planet, Hamlet’s auroræ are equatorial rather than polar, although they do occur around two localised areas on opposite sides of the equator.

One thing I seem to have been right about is that Hamlet contains a vast water ocean, although it is mixed with ammonia, altering its freezing point. Of Neptune, a rather similar planet in many ways, Olaf Stapledon once said, “. . . the great planet bore a gaseous envelope thousands of miles deep. The solid globe was scarcely more than the yolk of a huge egg”. Hamlet and Neptune are by far the two most similar planets in the System, and this is equally true of both. A major fact about both which is almost completely ignored is that it rains diamonds. What happens is that methane is compressed, squeezing out the hydrogen and causing the carbon left behind to form into diamonds under the extreme pressures. These then fall through ever-hotter layers towards the core, where they vapourise, bubble up through the ocean and recrystallise at the top. This also means there may be “diamond-bergs” floating on the ocean. I used the tendency for gas giants to form diamonds in this way in my novel ‘Replicas’, where diamonds have become a monetarily worthless byproduct of the deuterium and helium-3 mining industry on those planets. ROT13’d text spoiler: Zryvffn raqf hc bjavat n qvnzbaq znqr sebz ure cneragf’ erznvaf, fuvccrq onpx ng terng rkcrafr sebz Nycun Pragnhev gb Rnegu, juvpu vf cevpryrff gb ure ohg nf n cenpgvpny bowrpg vf cenpgvpnyyl jbeguyrff. https://rot13.com/. The diamonds may also be floating in a sea of liquid carbon. If this is so, or if there’s a whole geological layer of diamond, it could explain why the magnetic field is so different.

It takes over two and a half hours for a radio signal to pass between Hamlet and Earth, and the round trip is of course twice as long. Voyager 2’s transmitter is about as powerful as the light bulb in a fridge at 23 watts. This is stronger than a mobile ‘phone signal but way weaker than most radio stations. It works over such a long distance because the dishes used are aimed directly at each other, the frequency is free of interference by other human-made signals and the antennæ are very large. This could’ve been mentioned at any point in a number of my recent posts, but it may as well be here. In the case of Hamlet, this single spacecraft is responsible for practically everything the human race knows about the planet, and it relies on that tiny gossamer thread of a radio signal sent in the mid-’80s from two light hours away by a transmitter as weak as a dim filament light bulb. The initial baud rate was about 21 kilobaud, reduced in the end to a mere one hundred and sixty bits per second. They’re pretty amazing ships.

The Voyager mission to Hamlet was overshadowed by tragedy. Its closest approach took place on 24th January 1986, when I was at the height of my arguments with the fundamentalist Christians I met at university (that is relevant, as you’ll see). The Challenger disaster occurred on 28th, and was reported some time in the afternoon. I first heard of it as I was queuing for dinner at my hall of residence, and the kind of “head honcho” Christian student responded that it was “good” because it would persuade people to focus on and spend money on more pressing things. Whereas that’s a common and valid opinion I happen not to share, there’s a time and a place, and I get the impression he was saying that for shock value, which doesn’t seem very Christian by any internal standard. That, then, is my abiding memory of the Challenger disaster, and regardless of the value or priorities of NASA’s Space Shuttle program, the fact remains that seven people lost their lives that day, and of course anyone’s death diminishes us all.

A tangential result of Challenger was that it eclipsed the news from Voyager 2. It was also intimately connected with it in that NASA was inundated with letters requesting that the newly discovered moons be named in memory of the Challenger astronauts. This didn’t happen, even through coincidental Shakespearian characters having the same names. It was a factor in this naming proposal that there was a teacher on board, as many people who were children at the time were watching the launch live on TV due to this connection. It’s also a little-known fact that NASA almost sent Big Bird of Sesame Street, in character, on this flight. In 1988, the IAU, an organisation I currently like less and less the more I hear about it but maybe I’m being unfair, and it is after all an organisation and those are usually bad in some way, voted not to adopt the names of the astronauts for moons because they weren’t international enough. This might seem to make some sense until you consider that they’re actually named after Shakespearean (sp?) characters, which are of course associated with England, so their decision didn’t actually make much sense. However, at least some craters on the far side of Cynthia got named after them.

Hamlet has rings. Although they seem quite different to Saturn’s from a distance, close up pictures are hard even for experts to distinguish between at first glance once the image’s dynamic range has been boosted, because they show the same ringlet structure and there are also at least two shepherd moons, Ophelia and Cordelia. The rings are labelled using Greek letters and numbers, apparently without particular regard to their order. From inner to outer they’re referred to as ζ, 6, 5, 4, α, β, γ, δ, λ, ε, μ and ν. I presume this anomalous order is connected to their order of discovery because the way I remember them from the early ’80s they were named from α to ε. This also seems to continue the tendency to call things to do with the planet odd names, as it seems more logical either to number them or give them letters but not mix the two. The outermost two are red and blue respectively and the rest are dark. The first five, α to ε, were discovered on 10th March 1977 when the planet crossed in front of the star SAO 158687 and it blinked on and off regularly on either side of the planetary disc. However, a ring had been reported much earlier, by William Herschel, although this may have been imaginary because they’re very dark. The ν (Nu, not “Vee”) ring is between the moons Rosalind and Portia, so they also count as shepherds. The fact that most of the rings remain very narrow but don’t have shepherds is unexplained. Before their discovery, only Saturn was thought to have rings. After Jupiter was also discovered to have a ring in 1979, the question was whether Neptune would be the odd one out in lacking them. From that point onward, I assumed Neptune had them. Nobody knows what they’re made of, except that they can’t be ice, because their colours are unusual and don’t yield definite spectra to go on. Their darkness suggests they’re carbon-rich, and in conjunction with the probable diamond-bergs and liquid carbon ocean show that Hamlet is well on its way to being a carbon planet.

Most of the light is reflected by the ε Ring, which is also the most elliptical and the one closest to the equatorial plane. It’s brighter in some areas than others due to that eccentricity and varies in width. It’s possible that this variation translates into arcs – curves – rather than rings for other planets, perhaps orbiting other stars, or maybe Neptune. I can assure you that by the time I come to Neptune I will know if this is so. This is the ring with the first discovered pair of shepherds. The next brightest rings are α and β, which also vary in width, being widest 30° from their furthest points from Hamlet and narrowest 30° from their nearest. It’s probably coincidence that these angles correspond to those of the planetary magnetic field, or if not, something to do with a similar but separate dynamic process. Both these rings are somewhat tilted and are ten kilometres wide in some places, which raises the issue that they were detectable from three milliard kilometres away even though they were smaller than the Isle of Wight. The γ Ring (I’m just going to deal with these in alphabetical order, which means mentioning the 1977 ones first) is narrow, almost opaque and thin enough to make no difference to stars crossing when it’s edge on. This also means it isn’t dusty. The inner edge particles orbit six times for five of Ophelia’s orbits, so there seems to be a relationship there. As for δ, it’s circular, slightly tilted and may contain a moonlet because it seems to have waves in it. It has a more opaque and narrower outer part and a wider and more transparent inner side, which seems to be dustier.

Before Voyager 2 got there, the team who discovered these first five rings found a further three rings by the same method. For some reason these are known as 4, 5 and 6 even though five were already known by that point and there was a Greek letter naming scheme going on from the same team. I don’t understand this, but there it is. Voyager 2 found another two, fainter, rings, the naming scheme going back to Greek letters, and in this century the Hubble Space Telescope found two more. Rings 4, 5 and 6 are up to dozens of kilometres away from the equatorial plane and are inner and fainter to the ones discovered in ’77. They’re also narrower and don’t occult starlight edge-on. The μ Ring is blue and contains the moon Mab, around which it’s also brightest so the chances are it’s made of bits of that moon. These rings are dusty. Finally there’s 1986U2R, because of course it would be called that wouldn’t it?

The rings don’t form a stable system and given what’s known about them should disperse within a million years. However the fact that all the other gas giants have rings suggests either that having rings is normal for such planets or that they’re temporary but very common. Hamlet’s system generally, including the moons, is not so dominated by ring-related factors as Saturn’s although there are several harmonies, operating between small inner moons and the rings rather than the larger classic moons observable from Earth. A moon the size of Puck would be enough to provide the material for the rings, and Mab is actually currently breaking up and forming another ring, so it isn’t that peculiar. There are probably moonlets up to ten kilometres across within each of the rings. I presume the dimness of the sunlight out there combined with the darkness of the satellites and other material makes them harder to detect optically than small moons of Jupiter and Saturn.

Getting back to Hamlet itself, it’s methane which gives it that colour, but the atmosphere is in fact mainly hydrogen and helium like the other gas giants. It’s the second least dense planet and has a cloud top gravitational pull of only 89% of our sea level gravity. There are four layers of cloud corresponding to increasing temperature and atmospheric pressure. At slightly above sea level pressure, there are methane clouds. Considerably further down are the deepest clouds which have been actually observed, where the pressure is equivalent to the Earth’s ocean’s sunlit layers’, and are made of hydrogen sulphide. Appropriately for the planet’s official name, these would stink of rotten eggs. These share the layer with clouds of ammonia, which has an acrid, stinging odour. Below that is ammonium hydrosulphide, and finally, at a level where the pressure is equivalent to about four dozen times our sea level pressure, there are clouds of water vapour. The atmosphere is probably the most featureless of any solar planet’s, but does show the occasional white cloud, as can be seen in the photo at the top of this post. It’s also quite clear compared to all the other gas giants’, Titan’s and Venus’s, though not ours or the Martian one. I would expect there to be a level where one would find oneself completely surrounded by blue-green with various species of cloud. There are also traces of complex hydrocarbons as would be found in mineral oil and natural gas on Earth. Unlike other collisional atmospheres, Hamlet lacks a mesosphere, which is normally found between the stratosphere and thermosphere. There is a hydrocarbon haze in the stratosphere.

The chief distinguishing feature of Hamlet’s atmosphere is its featurelessness. Voyager 2 only detected ten clouds over the entire planet as it flew past. All the other gas giants have more stuff going on in theirs, and this is probably why it took so long to work out its rotational period of seventeen hours. There is a whiter polar cap from around half way between the equator and the poles, which swaps over between north and south as the orbit wears on. Voyager 2 was unable to observe the northern hemisphere because it was night there when it passed, so not only has Hamlet only been visited once but also half of it hasn’t been observed close up at all. In the decade or so after Voyager left, things started happening in its atmosphere but of course they couldn’t be seen as well as they would’ve if they’d taken place when it was there. I feel like there’s a kind of theme emerging here. Also, astronomy has only been advanced enough to make much meaningful sense of what’s going on since the 1950s, which is less than an entire orbit ago, so a whole cycle of seasons has yet to be observed. There has been a dark spot like the one on Neptune, and there are thunderstorms. It’s also possible that there’s a convection layer blocking the internal heat from the outer reaches of the planet.

So that’s Hamlet, such as it is. Next time I’ll be talking about its moons. I have two questions for you though. Did you feel that avoiding the name “Uranus” made you feel differently about this planet? I’m not sure about calling it “Hamlet” either, but that does at least circumvent the issue. Could you think of a better name or is it a bad idea to fixate on it so much?

Chiron And The Centaurs

‘Abigail’s Party’. ‘Calling Occupants Of Interplanetary Craft’. ‘Image Of The Fendahl’. The Southern TV broadcast interruption. The linking of three ARPANET nodes via TCP/IP. And Charles Kowal the astronomer discovers Chiron. That was November 1977 CE.

Partly due to ‘Star Wars’, 1977 was quite a “spacey” year. It was the year after the Viking lander and incidentally the US Bicentennial, and popular culture began to be invaded by SF and space opera themes, as characterised by space disco. A few weeks after the discovery of the planetoid, certain viewers of ITV Southern, but frustratingly not me because I was watching the ‘Horizon’ documentary on Von Däniken at the time, were informed by an apparent alien that their planet was in trouble and needed to throw away its nuclear weapons, but these two things happening at the same time is a telling example of how space-obsessed everyone was. I have visited this exact time period before on here.

Unlike the other objects orbiting the Sun I’ve mentioned on this blog, as opposed to some of the moons, Chiron was discovered within my lifetime. It was also discovered at a time when few new Solar System bodies were being found. A moon now called Themisto had been detected in 1975 but was lost before its orbit could be plotted, and Charles Kowal himself discovered the tiny Jovian moon Leda on 14th September 1974. Kowal worked at the Mount Palomar observatory in California with its famous 200″ reflector telescope, at the time the most powerful optical telescope humanity had ever built, but his prowess in astronomy at the time was legendary even if he had help from his hardware. Consequently, for me the discovery of Chiron was quite momentous, particularly as I was only ten at the time. It was the first time I experienced the discovery of a new object, and in fact a new kind of object, neither orbiting a planet Sun independently nor associated with the asteroid belt. For a while, before it was named, I called it “Lawok”, which is “Kowal” backwards, on the basis of the asteroid Ekard, which was discovered at Drake University. I think there may be other examples of reversing names for asteroids. Somehow I also expected people to understand what I meant by this name I’d just made up. I was a peculiar child, and am no doubt a peculiar adult.

Astrologers were quite taken with Chiron, perhaps because it was so novel, and rapidly compiled an ephemeris. The conjunction of the ’70s and the discovery of a new “planet” was bound to lead to this kind of thing. In fact there’s more information about the place astrologically than there is astronomically, so little known is it. Chiron has its own sigil:

⚷

This is based on the letters “OK”, for “Object Kowal”, but looks like a key to me. Maybe I should’ve talked about the other sigils before I reached this point, and in fact maybe I should just be covering every object which has one. Because of the fact that the centaur Chiron was a healer, Chiron the planet represents the wounded healer, something I identify quite closely with as a herbalist, and I suspect something which chimes with other herbalists, some of whom got into the profession in connection with their own chronic conditions, but this is not homeedandherbs and I won’t be digressing too far into that. Something that puzzles me about Chiron as a name is that I can’t tell if it was applied before it was realised that it was one of several such bodies and also that it was a kind of hybrid of two types of object, i.e. a centaur. I should also point out at this stage that Phœbe is also, physically speaking, a centaur and apparently also about the same size as Chiron, which right now I think is the largest centaur.

There is no good picture of Chiron. I very much doubt it was in a good position to be visited by the Voyager probes during the Grand Tour and in any case was discovered a few weeks after they were launched. The above, heavily pixelated image, was taken by the Hubble Space Telescope and is the best available. It’s still possible to extract some information from such an image because of fluctuations in brightness and colour as the object rotates, giving a vague impression of surface features. This was done with Pluto before New Horizons got there. Rotation period in particular is fairly straightforward provided the axis isn’t too inclined towards Earth. From this it can be gleaned that Chiron’s day lasts almost six hours. Its year is around fifty of ours. Its orbit is more eccentric than any planet’s, including Pluto, and it spends most of its time outside the orbit of Saturn, dipping inside it for a while. I say “a while” because I can’t do calculus and therefore can’t calculate how long that is. Its orbital inclination of six degrees is greater than that of any planet other than Pluto. At its greatest distance from the Sun it’s further out than the next planet (I will get to why I haven’t called that by its official name in a future post).

When I posted about Titan, I mentioned Chesley Bonestell and the difficulty of depicting worlds about which little was known other than their brightness from Earth and their orbital characteristics. In many cases in the Solar System, this is now resolved, as every planet has now been visited along with several dwarf planets, and also all of the larger moons except possibly Pluto’s. Before that happened, however, a large amount of guesswork was required. The largest body outside the asteroid belt this is still true for is Chiron. Incidentally, you may have noticed that I don’t number minor planets in what I’ve written, but on this occasion it would be ambiguous for me not to point out that the Chiron I’m referring to is not the hypothetical moon of Saturn but 2060 Chiron. Anyway, a lot of what can be said about Chiron is still in that vein, and in that respect the body in question is unique for anything large between the orbits of Jupiter and Neptune. Without a dedicated mission, nothing is likely to pass near the centaur, and only five probes have got beyond the orbit of Pluto. Since its discovery, most of a Chironian year has passed so it was in theory possible that one of them would have visited it, but the probability is very low.

This guessing game is not quite as bad as it used to be with the smaller worlds of the outer system before the space age because it so happens that Chiron (“2060 Chiron” if you insist) is not actually a typical centaur. It’s much closer to being a comet than average. During its summer it develops a coma. This, meaning “hair”, is the temporary slightly cloudy atmosphere which develops around a comet as it approaches the Sun, caused by some of its surface evaporating in the heat. This ultimately puts paid to a comet, a good example being Encke with its mere three year period, which is not doing well. Meteor showers are the remains of comets which have evaporated because of this. I would conclude on this basis that Chiron itself is a short-term member of the system, but this also seems to imply that there are meteor showers out there in deep space orbiting the Sun independently which used to be centaurs but have more circular orbits than the average comet, so it would take longer. In Chiron’s case, millions of years of evaporation may mean that it used to be a dwarf planet, although it’s now far too small. It also develops a tail like a comet.

One surprising thing about the place is that its spectrum shows no water ice at all, which is unusual for an object in this zone. It’s actually similar to a C-type, or carbonaceous, asteroid, a composition shared with Halley’s comet. You have probably gathered by now that the hybrid nature is between that of an asteroid and a comet. Chiron is not just referred to as 2060 Chiron, an asteroid designation, for this reason and is also considered a comet and named appropriately as 95P/Chiron. It can be compared and contrasted with a comet. In terms of composition, it’s very similar, but comets orbit in elongated elliptical orbits taking them into the inner system and out much further, on the whole, although there are also short-period comets like Encke which don’t get outside the asteroid belt. Centaurs, and apparently Chiron in particular, have less comet-like orbits which range between approximately Saturn and the next planet out (I’ll get there, don’t worry). Their orbits are more circular and this has consequences.

Chiron may also be ringed, and may also not be the only ringed centaur. It was initially thought that fluctuation in the brightness of stars in front of which Chiron passes could be explained by the venting of vapours from the surface as it heated up, so there were jets causing the stars to dim, but this hypothesis has now been rejected in favour of rings. They seem to be about seven hundred kilometres in diameter and to be quite sharp-edged. It shares this ringedness with at least one other centaur.

There are proposed missions to Chiron but so far as I can tell, nothing firmly planned, at least as of yet.

Chiron is not in fact the largest centaur. Chariklo, which is also probably ringed, is about three hundred kilometres across. It orbits quite a bit further out than Chiron. Both centaurs have a pair of rings, rather larger in Chariklo’s case.

Centaurs are defined as small solar system bodies orbiting between Jupiter and Neptune. Their orbits are generally unstable over a period of millions of years. I’m not sure why this is. On the one hand, cometary orbits tend to be unstable, so it sort of makes sense that centaurs would be as well, except that they don’t have elongated orbits. On the other, the contrast between the inner and outer systems is that the former is more crowded but has less massive planets whereas the latter is less crowded but has more massive ones. I’m not sure which would make more difference to the movement of objects between them, but it seems calculable. For instance, Jupiter is the most massive planet and is separated by a minimum of five AU from Saturn, the second most massive. Jupiter is 318 times as massive as Earth and Saturn ninety-five. Venus and Earth are the first and second most massive inner planets and the halfway point between them is 0.15 AU, roughly. This means that the scale of gravitational attraction is comparable in both situations. This line of thought doesn’t seem to lead to any firm conclusions.

Centaurs can be classified into three different groups by colour. They can be red, blue-grey or have unknown colour indices. The third category seems to be due to lack of information. Chiron is one of the bluest such objects, and is incidentally a similar colour to Neptune’s moon Triton. Pholus is a similar colour to Mars and Phœbe is one of the bluer ones. It isn’t known why these two groups exist, but possible explanations include the influence of cometary activity such as the development of comæ which lead to the loss of certain materials, the effect of space weathering, i.e. solar radiation causing chemical changes on the surfaces, or just being made ab initio of different substances. This vagueness reflects the lack of information available on them.

Another example of vagueness is the uncertainty about how many of them there are. Estimates vary between forty thousand and ten million objects over a kilometre in diameter ranging between Jupiter and Neptune. Bearing in mind that space is not two-dimensional, this region projects onto a flat ring on the ecliptic (the plane of Earth’s orbit, which is close to that of seven other major planets), an area of 2761 square astronomical units. If there are ten million large centaurs, the separation between them, ignoring inclination to the ecliptic, would average at around 2½ million kilometres. If it’s as low as forty-four thousand, this figure approaches forty million kilometres. Either way, this “second asteroid belt”, as it were, is far sparser than the inner one. Another big difference between centaurs and asteroids is that the latter are more stable and long-lasting. With one known exception, or two if Phœbe is counted, centaurs are not permanent residents of their region, and perhaps surprisingly they are more volatile than asteroids, gradually evaporating and outgassing depending on their locations, even though their regions are much cooler than the asteroid belt. This raises a question in my mind as to whether there are solar systems with much more powerful suns whose asteroids are like this rather than centaurs, so there are rocky bodies which are gradually vapourising and comets made of rock and metal rather than being icy.

The fact that they’re unstable suggests that there is a constant external supply of new centaurs. This is not really news of course. I’d assume that the cloud of planetoids outside the orbit of Pluto, either the Kuiper Belt or the Oort Cloud, is the source of these bodies and that they’re drawn into the planetary part of the system in the same way as comets are, i.e. by the gravitational influence of larger outer planets and to some extent nearby stars. At this point in the journey through the Solar System, the influence of other stars starts to become noticeable, even though they’re still astoundingly distant. It’s also felt through the appearance of comets in the inner system.

It’s possible that not all of the centaurs existed originally in their current form. Some of them may be fragments of larger bodies which have disintegrated through the gravitational influences of the gas giants, and at least one of them may have done the opposite of a Phœbe by escaping Saturn’s gravitational capture and taking on a solar orbit of its own. My impression of the different types, and there isn’t much information to go on, is that they arrive in their new orbits in forms less influenced by the higher temperatures and radiation from sunlight and proceed to be aged by the relatively warm environment of cis Neptunian space and possibly also by being yanked about by the giant planets, and eventually succumb to the ravages of the planetary part of the system, by which time interstellar perturbations have brought more centaurs into it.

Chiron is usually stated to be the first centaur discovered, but apparently this is not so. In 1927, a peculiar “comet” was found, now referred to as 29P/Schwassmann-Wachmann, or Schwassmann-Wachman 1, estimated to have a diameter of about sixty kilometres and an unusually broad and circular orbit for a detectable comet between Jupiter and Saturn. As such it would be unusually close to the Sun for a centaur. Around seven times a year, it suddenly becomes much brighter for about a week at a time. Nowadays it would’ve been considered a centaur, although it’s quite a peculiar one since it’s almost as close to the Sun as Jupiter. There is also a family of comets associated with Jupiter, whose periods are less than twenty years, and Schwassmann-Wachmann 1 can be considered a comet as well.

Quite a lot of centaurs seem to have a diameter of around sixty kilometres. Although none of them currently seem to be greater than about two hundred kilometres across, and there are only a couple of those, it’s been suggested that Ceres used to be one. If this is true, Ceres is far bigger than any current centaur, by a factor of about sixty, and prior to reaching its current position would’ve been even larger due to greater ice content. Nonetheless it is true that Ceres is not like other objects in the asteroid belt.

One asteroid I’m quite curious about in this respect is Hidalgo. This is more an “unusual object” than anything else. It could count both as an asteroid and a centaur, and as far as I know is unique in that respect. It commutes between the asteroid belt and the centaur region, near Saturn and within Jupiter’s orbit. Again, it’s around sixty kilometres in diameter, and is a carbonaceous asteroid (or centaur).

Due to the lack of information generally available on centaurs, that’s most of what I might say about them without venturing into the realm of tedium. I’ll just mention that tholins are what make them red, and the possible link with plutinos, which I will get to.

Next time: the planet with the silly name.

The Yin-Yang Moon

Saturn’s third largest moon was already known to be peculiar long before any spacecraft reached it. This was because its brightness seemed to vary so much. It was noted that it was six times brighter when east of Saturn than when west of it, and it emerged that the moon had one black hemisphere and one white one, in 1671 by Cassini when he discovered it. It’s the outermost of the four Sidera Lodoicea. After it the only substantial moon is Phœbe.

It’s also Saturn’s third largest moon, but is considerably less dense than Rhea or Titan at only 9% greater than water. You might also notice that in those two photos there is a triangular projection at the equator. This is the profile of the ring that goes around the world at that latitude. And of course there is a large crater in the light hemisphere with a central peak and a smaller one near the south pole. The moon as a whole, like most apparently spherical worlds in the system, is in fact slightly wider across the equator than between the poles even ignoring the ridge, with a deviation of 4% from perfect sphericality compared to Earth’s 0.3%

Although I’ve said the hemisphere is black, and it’s certainly very dark, but in fact practically nothing is truly black of course, and in fact it’s a very dark red. A fairly evident question to ask is whether it’s a light moon with a dark coating, a dark moon with a light coating or just made up of two different substances. Its symmetry suggests very much that the latter is not so and that the chances are dark matter (not that kind) was deposited on the leading hemisphere from somewhere else. In particular it can be seen to coat the rims of craters at the edge of the hemisphere on one side and the floors on the other. However, there is also a ring of material on the trailing hemisphere, which is harder to explain with the hypothesis that it’s being deposited from an extraneous source. It’s been suggested that it’s from Phœbe, but that’s a very small moon and never comes closer than seven million kilometres to Iapetus. The composition is also very different. There seem to be no craters at all on the dark side at first, but in fact this is due to the colour making it difficult to see them. The situation, in fact, is rather similar to that on Cynthia, with all the maria on the inboard hemisphere but a few patches on the outboard. In the case of Earth’s moon, the material of the maria was extruded from the interior, kind of – they’re lava fields. However, on Iapetus the distinction is between leading and trailing hemispheres rather than the one facing Saturn and the one facing away, which is why it’s so noticeable from Earth. The colour of the material is closest to that of Callisto. The arrangement actually is similar to the Yin-Yang symbol:

The dark side of the moon is something like ten times darker than the bright side. It’s also organic and contains nitriles, similar to some of the compounds found in Titan’s atmosphere. The spectrum is similar to that of the outer belt D-type asteroids, some of which may originate in the Kuiper Belt around Pluto and beyond. It’s a few decametres thick in some areas, possibly more elsewhere. It kind of reminds me of some kind of bacterial culture growing across the moon like it’s a petri dish but I wouldn’t suggest for a moment that it’s actually alive. What may have happened is that water ice may be slowly evaporating from the surface, leaving behind a residue. The temperature range on Iapetus is the widest in the Saturn system because of its unusual orbit. The moon is more tilted than the other large moons and takes seventy-nine days to orbit, which means its day also lasts that long, leading to daytime temperatures warmer than anywhere else and night time temperatures colder. During the day, the temperature gets as high as -144°C in the dark area and -160°C in the light. It seems, then, that nobody really knows what causes it.

This is a closeup of the equatorial ridge, which amounts to a mountain range. This is up to twenty kilometres high, in other words higher than Everest, twenty across and 1 300 kilometres long, and is thought to be a collapsed ring. Iapetus is thought to have had a ring like Saturn’s, though much less spectacular of course, which ended up falling onto the surface many millions of years ago. It isn’t the only ridge on a Saturnian moon. Pan, Atlas and possibly Daphnis also have them, but all of these are very small and close to the rings. It means, basically, that there is a tendency for moons circling Saturn to be ringed, though not just with the discrete particles which may be present around Rhea but with equatorial ridges which are the remnants of crashed rings. These have never been found outside Saturn’s system and may result from ring material from Saturn itself landing on the surface, or it may be that it had its own moon which broke up and dropped to the surface in bits. There are a few more things to say about the ridge on Iapetus. One is that it’s only on the dark side, but there are partial rings so that may still make sense. Another is that it may or may not have roots. Earth’s mountains extend deep into the crust because they would otherwise not be balanced – they’re floating on the mantle and therefore are a bit like icebergs except that only half of them is below the surface. It isn’t clear whether it’s also true of this ridge. It’s also notable that Iapetus has a weird orbit with a high tilt and a lot of space between it and Hyperion, which would enable it to build up a large undisturbed ring system. It would be possible to see the curvature of the moon from on top of the highest parts of the ridge.

Although it isn’t dramatic, Iapetus has a more tilted orbit than the other large moons of Saturn at about fifteen degrees to Saturn’s equator. This makes it the only moon with a proper view of the planet’s rings, but unfortunately because it’s also so far out, Saturn and its rings are quite small in the sky, so you can’t win really. It seems like this pattern would be repeated throughout the Universe. Ringed planets are likely to have close moons whose view of the rings is poor because they’re edge on, and further moons which aren’t but in whose skies their planets will be relatively small and unspectacular. However, this does raise the question of where the ring material came from, since Iapetus is nowhere near the rings and doesn’t orbit in the same plane of even quite a sparse ring. However, there is a very sparse ring around the orbit of Phœbe which extends into the orbit of Iapetus, and if kicked up from Phœbe will be orbiting in the opposite direction from Iapetus, whose orbit is normal in that respect. This means Iapetus would encounter the material coming much faster the other way. Moons with such tilted orbits are usually small and lumpy, and it’s worth comparing Iapetus with Neptune’s moon Triton. Triton also has a highly tilted orbit but moves backwards compared to most other moons and has a lot in common with Pluto, so it’s probably a captured planet rather than a moon which formed in Neptune’s vicinity. The same does not appear to be true of Iapetus because it’s relatively small and orbits in the same direction as the other large moons. It’s tempting to imagine that the same mishap caused the ring to collapse onto the surface, gave it a dark and light side and caused its orbit to tilt, but what that was, if it happened at all, who knows?

Landslides on Iapetus are common and tend to move slowly over long distances. This is not unusual and also occurs on Mars, Venus and elsewhere. These are called sturzstroms and may be partly extended by the particles skating across the ice, and they may in any case be quite finely-grained. It’s like the material is a liquid spilling out and flooding over a flat plain, and it comes to mind that this is what happened with the lunar maria, so the comparison with Iapetus might extend quite far. The height they fall from is a twentieth or less of the distance they end up travelling, and they happen in smaller craters. They leave behind gaps in the rim walls, where the rim is still there but the slope leading up to it has slid down, leaving a steep edge on the inner side. This even happens on the equatorial ridge, except for the “inner side” bit because it hasn’t got one. They’re the largest landslides in the Solar System on any icy body. I have to admit to being rather puzzled about this right now because Iapetus seems like quite a quiet, uneventful place. Whatever the cause, what seems to be happening is that the friction among the particles and between them and the base heats them up and softens them, which lubricates the movement somewhat. The shape of these landslides is similar to our own oceans’.

The moon is only one-fifth rock and is likely to be solid all the way through. There often seems to be a situation with icy moons (and possibly also the likes of Pluto) where the density is likely to increase somewhat as non-icy meteorites impact them, and it’s complicated to consider the question of whether this happens faster with smaller moons than big ones. On the one hand, each meteorite makes a bigger difference to a small body, but on the other it’s a smaller target. This might also apply to the relative size of craters. The surface of Iapetus is mainly water and dry ice, iron and iron oxide. Presumably this is true of the lighter hemisphere and the layer below the dark red matter on the dark side. The size of particles on the light side create Rayleigh scattering like blue eyes and skies, and this results in a multicoloured surface, although it’s quite unsaturated. In other words, the light side glitters like diamond. This could also mean there’s a little Cherenkov radiation, which is where subatomic particles exceeding the local speed of light in a medium stimulate the emission of blue-white light like a sonic boom. There is also more dry ice the further into the trailing hemisphere you go. On the dark side, there is nanoparticle hæmatite and iron. I find this somewhat odd because it seems to mean there are two different kinds of red material on that side, so does this mean there is a tendency for solid matter to be red? It kind of makes sense that there is in the case of mixtures, because a variety of different compounds are more likely to be different colours and mixing them together leads to the “brown splodge” effect you get with paints and inks. Brown, of course, is somewhat red. However, this raises the question of why mixtures tend towards the red end of the spectrum. All that said, the fact remains that there are two types of red substance on the dark side, only one of which is a mixture. Whatever it is, all the dark material in Saturn’s system, including the darker rings, seems to be made of the same stuff as it’s all spectrally similar.

The prominent basin (or crater) in the southern hemisphere on the light side is called Engelier. It’s five hundred kilometres wide. However, there’s an even larger one on the dark side called Turgis, almost half of the moon’s diameter at 480 kilometres. This is odd because that makes Turgis one of the largest craters in the Solar System but it’s far from the most prominent, probably because of the dark material over it. The crater is a site of landslides, also found in the smaller superimposed Malun crater. Turgis interrupts the ridge, which only occurs on the dark side, and there’s a small stretch on the other side of the crater. Engelier is “on top of” a faintly outlined crater called Gerin.

The light side is divided into two “terræ”: Roncevaux in the north and Saragossa in the south. The entire moon has about the same surface area as Australia, so if each “land” is half the light hemisphere they will have a surface area about three-quarters the size of Kalaalit Nunaat (Greenland), Earth’s largest island. They also share with that island the feature of being covered in white water ice. Saragossa’s most distinctive feature is Engelier. Both of them cross their respective poles, so again they resemble the terrestrial island in being partly polar. The division between Saragossa and Roncevaux could be thought of as where the ridge would be.

I’d like to finish by addressing a topic I probably should’ve started with: the name Iapetus. I pronounce it /i’apətəs/, but recognise that most Anglophones say it with a long, diphthong I at the start: “eye-A-pettus”. Arthur C Clarke’s ‘2001 A Space Odyssey’ originally envisaged the second monument to be situated there, but spelt it “Japetus”. This is an older spelling, dating from the time before I and J were separate letters. Iapetus is also, like Tethys, the name of a prehistoric ocean on Earth, circumpolar in the Southern Hemisphere separating landmasses which are today on opposite sides of the Atlantic and is therefore named, like the Atlantic Ocean, after a titan. The Iapetus Ocean was present from the late Precambrian until the Silurian.

Iapetus the titan seems to be linked to Japheth the son of Noah. The name means “piercer” and his sons were seen as the ancestors of humanity, with their worst qualities exemplifying those of human beings, so there seems to be a definite link between the myth as recorded in Torah and in Greek myth.

Next time (but one): Phœbe – moon with a fiddly letter in its name.

The Izzle Of Wiggot

We’re often told about something being the size of a football pitch, an Olympic swimming pool or Wales, or the length or size of a double decker bus, or several. In terms of mass, there’s much talk about Afrikan elephants. One such unit is of course the Isle of Wight, shown above in a photo from the International Space Station. In particular, in around 1910 CE, the observation was made that the population of the world could stand on the island. It was later noted, in 1968, that the information was out of date and the Isle of Man would now be required, and that year, John Brunner wrote his memorably titled novel ‘Stand On Zanzibar’, which estimated, as it turns out almost perfectly accurately, that by 2010 the seven millard people on this planet would require the floor space of the East Afrikan island of Zanzibar. These three islands have areas of 381, 572 and 1554 km² respectively.

Of the various units of area used, the Isle of Wight is not particularly common. From 1974, it became its own county, but it’s long been a familiar and discrete unit, particularly for people living in the English Home Counties. I understand that in the US, Martha’s Vineyard tends to be used. It has certain advantages over “the size of Wales” because that country has a largely politically defined border and there may in the past have been issues with Monmouthshire, a place which totally does my head in but has several significant personal associations for me which mean I can’t ignore it. As far as I can tell, Monmouthshire is now absolutely Welsh territory, but for a long time its status was ambiguous, and I can remember a late nineteenth century gazetteer repeatedly referring to “Wales and Monmouthshire” due to this confusion. Perhaps the issue of Monmouthshire will come up again on this blog.

A more precise definition of the statement that the population of the world could fit on the Isle of Wight is that 2 600 million people would occupy the island at a density of six people per square metre. This number was passed between 1951 and 1952, which is more recent than I expected. The issue of human population being a problem or not is another important matter which I plan to address soon, particularly in connection with the controversial documentary film ‘Planet Of The Humans’. There are cultural biasses in all these units, but this can be a good thing. For instance, deforestation is often quoted to the British in “Waleses”. A Wales, incidentally, is equivalent to 54½ Isles of Wight.

While I’ve been posting stuff about the Solar System, I’ve found myself using these kinds of units, particularly in terms of surface areas although there are some others. For instance, the Cassini Division in Saturn’s rings is about as wide as the east-west distance across North America at its widest point, probably roughly Vancouver to Nova Scotia. To some extent it may help to visualise the scale, but there also comes a point where it becomes impossible to relate to and one may as well just be saying “very big”. That said, it is startling that the maximum possible distance across Titan, for example, is roughly the same as London to Los Angeles, which feels like it’s practically on the other side of the world, and it’s fair to note that this is a slightly confusing statement because it isn’t east to west but across the Arctic, as an aircraft might fly.

Another issue, particularly with Wales, is that “if Wales was flattened out it’d be bigger than England”. The problem with this statement is that if England was flattened out it’d be bigger than England too, and the extent to which something is “flattened out”. Is it supposed to include just mountains and valleys imagined as pyramids or does it go down to the level of irregularities on the surfaces of grains of sand? How attached does a grain have to be to the rest of the surface? I’ve been into this before though.

Getting back to the Isle of Wight, I have the radio on as I’m typing this and it’s just been stated that an area of orchards the size of the Isle of Wight has been lost in this country since 1900. This shows how common this measurement is. It’s probably easier to relate to than Wales because it’s on the lowland side of the British Isles, so the whole flattened out issue doesn’t apply. Other linguistic spheres tend to use small local governmental units, perhaps their smallest such as Saarland, and may differ in that they are themselves not the official languages of island nations and therefore less focussed on islands and coastlines even though on the same scale their coastlines may be longer, as with Norway, so they lack “natural” geographical units of the same prominence. Denmark, I think, tends to use Bornholm. In terms of the “U”K, we have Rutland and Clackmannanshire, but the latter is as far as I know never used in this way, partly due to the 1974 reorganisation even though that’s now past. Rutland also temporarily disappeared at that time but came back in 1997 thanks to an enthusiastic local campaign. It’s a single square kilometre larger than the Isle of Wight.

The island was historically part of Hampshire and is not a ceremonial county. During the 1960s when metropolitan counties were being proposed, there was one suggestion which never got taken on board whereas all other suggestions were: the Solent area was considered as a metropolitan county. I don’t know if it would’ve been called “Solent” or included the island, but if it hadn’t there would’ve been an odd division between two halves of Hampshire, so presumably the Isle of Wight would still have become independent. Incidentally, the Solent area now has a population of 750 000, so it does seem valid as a metropolitan county although it never happened. They were in any case abolished in 1986.

Historically, the island has cultural connections to East Kent, my own original local area. These are the two areas prominently settled by the somewhat mysterious Jutes after the fall of Rome. The Jutes are a poorly-known tribe compared to the Angles, Saxons and Frisians, whose name seems to be cognate with the Goths and Geats (as mentioned in ‘Beowulf’). They’re also rumoured to have suffered a genocide and to have therefore made little contribution to modern English culture although they are responsible for the division between maids of Kent and Kentish maids. Jutes were the maids and men of Kent, so to speak. I’m wondering if they were massacred for refusing to convert to Christianity.

I described Telesto and Calypso, Dione’s coörbitals, as both around the size of the Isle of Wight, but comparing a small celestial body to the island is ambiguous. Does it mean surface area, volume, or perhaps mass? A sphere with a surface area the same as the island would have a diameter of nine kilometres, which is quite a bit smaller than Telesto or Calypso.

By Mikenorton – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=26055216

This is a geological map of the island. The multicoloured sands of Alum Bay should be enough to convince most people that it’s quite heterogeneous. This varied composition makes it quite difficult to assess its mean density and therefore mass accurately. The Needles are obviously made of chalk, whose density is 2.499 compared to water. It’s tempting at this point to go off on a tangent and attempt to describe the island as if it’s a tiny moon of this planet, but I shall resist that. Nonetheless I do want to know how large and heavy it is.

As usual, I have little idea what’s known generally or just to me, so I may be recounting common knowledge here but if not, in the ‘noughties there was a Radio 4 sitcom which was mainly a parody of television science fiction tropes, called ‘Nebulous’. The central character, Professor Nebulous, has a backstory of accidentally destroying the Isle Of Wight by moving it ten kilometres to the left so it can get more sunlight, killing the whole population in the process and severely maiming one of the other main characters, Harry Hayes. This has made me curious about how much the island actually weighs. In order to decide this, it’s necessary to work out where it starts.

The Solent is between fifty and 120 metres deep and the Isle of Wight has an average elevation of about sixty metres, although St Boniface Down is 241 metres above sea level. I’m going to say, therefore, that the island is a prism with cross-sectional area of 381 km² and a total height top to bottom of 180 metres. I’m also going to assume it’s half chalk and half sandstone, although I’m aware it also contains substantial quantities of clay. The density of sandstone is up to 2.6, so a fair estimate is 2.55. Hence the volume of the island is only 68.5 km³ and its mass is just under 175 000 million tonnes. By this calculation, more than half of the island is below sea level.

Things can be done with these data.

Make the island a ball of rock. It then has a diameter of five kilometres and a surface area of eighty square kilometres, which indicates how flat and thin the real island is. This is kind of uselessly small for astronomical purposes. Both Phobos and Deimos are several times larger. If the Isle of Wight was orbiting us as a second moon, it would be relatively bright due to the chalk content but also very small. Perhaps people could live inside it in caves. It could have no external atmosphere and its gravity would be negligible, but it could be spun to give it artificial gravity. Unfortunately it wouldn’t do the squirrels much good and the fossil record would be . On the whole it doesn’t sound like a good idea. The population of the island is 141 606, and the question arises of whether it could be self-sufficient as a tiny moon. Perhaps if it were covered in greenhouses full of tanks of algæ. I’m not sure. I imagine the current inhabitants of the island would have something to say about it and wouldn’t be entirely behind such a plan.

As for the real Isle of Wight, I have been there on holiday and seem to remember being there on another occasion. This was in 1976. There used to be schools programme footage of me and my brother sitting on the jetty waiting for the ferry from, I think, Portsmouth. This was in July at the height of the famous drought. While there, I got tonsilitis and ran a fever, as did my brother, although I did manage to visit Blackgang Chine and the dinosaurs. Although it was difficult to find the holiday home, the small size of the island also made it fairly difficult to get lost.

To me, as a child, the Isle of Wight kind of marked the edge of the known world, or rather it was slightly beyond that edge. I was familiar enough with most of Kent and aware that Sussex and London were beyond it, and had visited them many times, but Hampshire and the island were not part of my local sphere.

That’s it really.

The Big One

All moons are special of course. That is, you can probably dredge something interesting up about most of the large ones. All that said, of all the moons in the system, all the planets in fact, Titan must be near the start of any list ranked by interest. Writing this post is in fact quite daunting because I want to do it justice, and having written a couple of thousand words even on somewhere like Rhea, which let’s face it doesn’t strike me as one of the more intriguing places, I now feel obliged to do this amazing world justice, and I can do that, but I may go on and on, which I do a lot.

I live in Loughborough, and consider it a very boring town. To be fair, even when I lived in Canterbury I considered it boring even though it had that big pointy building in the middle. A more positive approach would lead to one casting around for sources of pride regarding the place, and in the case of Loughborough there are a few things. There’s the Great Central Railway, which is Britain’s only main line double track heritage railway. There’s the Bell Foundry, which produces a large proportion of church bells in Britain. Ladybird Books were based here. There’s also a university, which actually I found quite unimpressive, and it’s next to the National Forest. The Carillon is also quite special. Some people also say Loughborough is where the North starts. As you become familiar with a place, you get to realise what makes it individual and special. Consequently I can imagine people living on Rhea, perhaps working for the Rhean Tourist Board, and coming up with bits and pieces which might attract sightseers such as the possible ring system, but there would probably be a lot of time and work spent on trying to promote the moon. Rhea is in a sense the Loughborough of Saturn’s system. Titan, by contrast, sells itself. It’s the London or NYC of the system. You don’t need to push it because it’s amazing.

The illustration at the top of this post, perhaps surprisingly, is in the public domain. It’s by Chesley Bonestell, whose matte painting for ‘2001 – A Space Odyssey’ I used on this blog yesterday. Bonestell was a prominent mid-century space artist who also worked on films. He also designed a number of prominent buildings and used his skill in cinematography to create masterful depictions of space-related scenes. He was influenced by the frontier style of art, where beautiful and almost deserted landscapes in North America would have small figures, horses and wagons depicting the European pioneers travelling across the continent to settle and raise food, so many of his pictures show astronauts, spacecraft and bases on the surface of various bodies throughout the Solar System and in space itself. They also serve as a record of the state of knowledge and expectations at the time. For instance, before the Apollo program it was expected that a non-staged rocket ship would land on the lunar surface and return in one piece. The staging concept is so familiar to us nowadays that we find it quaint to imagine anything else, but there was a time when a much more straightforward vision saw a finned and streamlined craft perhaps a hundred metres high setting out from Earth and coming to rest somewhere like the Sea of Tranquility. This is what Bonestell depicts.

In the case of views from the different moons of the Solar System, artists at the time had very little to go on. They had the angles of the orbits, the distances from the planets and a rough estimate of the sizes of the moons in question. There was a lot that could be concluded from the data available but on the whole this was quite tentative. Bonestell produced a series of paintings from the major moons of Saturn, which might be expected to be quite spectacular given the planet’s rings, but in fact like most satellite systems, most of the moons orbit close to the equatorial plane, particularly the closer ones, which has the unfortunate result that either Saturn is big in the sky but has hardly visible rings because they’re seen from edge-on or does show the rings from a suitable angle but is so far away that they’re not that impressive. Moreover, although he was, I’m sure, assiduous in collecting as much information as possible about all of his subjects, he didn’t have much to go on apart from those few facts. Therefore it’s not surprising that all these paintings focus on the appearance of Saturn in these moons’ skies.

As I say, I was very surprised that his view of Titan is in the public domain. It seems to me that this is one of his most iconic and famous paintings, and just being able to post it like that, though presumably in a lower resolution than is available online for a price, is quite amazing. Incidentally, this picture occupies a significant position on the wall of a NASA office in the film version of ‘The Martian’. I don’t know if it’s on the wall anywhere in the real offices but it is quite inspiring and classic, so I wouldn’t be surprised.

All that said, it is of course inaccurate. In particular, Titan is much cloudier than that and it’s unlikely that Saturn is ever visible from the surface. Moreover, this is a daytime picture and stars are visible in the sky. In reality they wouldn’t be because not only is there copious smog in the atmosphere, in a good way, but even if there wasn’t the atmosphere has several times the density of our own air at sea level, so there’s no chance, even above the cloud deck, that stars would be visible during the day. Moreover, Bonestell has a tendency to depict ice as it would appear in terrestrial conditions rather than how they are actually likely to be on the bodies concerned. By the time you get out to Titan, the temperatures involved are so far below freezing that water ice is basically just another rocky mineral. The average surface temperature on Titan is around -182°C. This is ninety-one degrees above absolute zero, and freezing point is three times that temperature. In proportion, Earth’s mean temperature is 22°C, and three times that is 612°C, and certain common terrestrial minerals have a melting point around that, such as quartz and mica. Water ice is not just frozen water, even on Titan’s surface. The shiny, snowy look is interesting but speculative, and turns out to be wrong. I feel bad criticising his art in this way, and I want to stress that I still think his paintings are amazing and wonderful.

The landscape is also craggy in a similar way to Bonestell’s representation of the lunar surface. This is also inaccurate. Not only did it turn out to be wrong in the case of Cynthia, substantially because of moondust and micrometeoroid impacts, but it’s even less accurate for Titan because in the latter world’s case there is liquid-based erosion there. Here’s the famous image from the Huygens lander:

These are basically pebbles, at least in the foreground, and this is because of the rôle of liquid in their erosion. This, of course, is part of what makes Titan so fascinating. It’s in some ways the most Earth-like world in the whole Solar System.

This statement, though it has a lot of truth to it, can also be quite misleading. Yes, Titan is quite Earth-like but also has important differences. In the novel ‘Imperial Earth’, Arthur C Clarke illustrated the difference between the two with a burning plume of flame. On Titan, it was an oxygen spout burning in a methane atmosphere but on Earth it could be a methane spout burning in oxygen. Nowadays we realise that the rôle of methane in the Titanean atmosphere is not as a main gaseous constituent, but it still works as a good metaphor. The same kinds of phenomena often exist – rivers, lakes, seas, rain – but not in the same way. These pebbles are eroded into rounded shapes just as they would be in a stream or on a beach on Earth, but they’re likely not made enitirely of silicates but ice and the liquid eroding them is methane, gaseous on our home world. It is possible that they’re mixtures of ice and stone, so we might think of them as lumps of frozen mud or clay, but that’s considering them in terrestrial terms. In Titanean terms this planet is a furnace covered in oceans of molten rock with clouds of the same in the sky raining liquid as hot as fire, at least as far as the surface is concerned.

Titan is the second largest moon in the Solar System after Ganymede. Unlike Ganymede, and uniquely among moons, not only does it have an atmosphere, but said atmosphere is somewhat denser than Earth’s and the surface pressure is almost twice as high as ours. It is in fact the only moon in the system with a proper, collisional atmosphere like our own. This raises the question of how come Ganymede has no real atmosphere and yet the slightly smaller Titan has such a thick one. I imagine the answer is twofold. Firstly, Titan’s a lot colder than Ganymede, and secondly it’s less exposed to the solar wind because it’s twice as far from the Sun, making it only a quarter of the strength. The molecules would be moving much more slowly in the vicinity of Titan than Ganymede’s, and consequently don’t escape its gravitational pull.

Although it used to be thought to have a methane atmosphere, and a considerably more tenuous one to boot, it turned out that the main constituent of the atmosphere is the same as ours: nitrogen. This presumably means there are plenty of worlds in the Universe with a mainly nitrogen atmosphere like our own. Methane, being liquid, performs the same kind of antics as water does on Earth, making Titan the only other world in the system with liquid bodies of water and also land on its surface. There are several planets with liquid on their surfaces, but none with both liquid and solid. The fact that there is liquid flowing over a solid surface presumably means the latter is shaped, as Earth’s is, into river valleys, oxbow lakes, potholes, caverns, perhaps fjords and so forth. However, there are other factors which make it quite different.

Titan’s surface gravity is about the same as Cynthia’s, though somewhat lower at a little under a seventh of Earth’s to Cynthia’s sixth. Although it’s larger than Mercury, that planet is joint densest with Earth so Titan, with a density less than twice water’s at 1.88, has considerably less pulling power. This is due to its higher volatile content, such as water and ammonia. This also means that if Cynthia were a moon of Saturn, it too would have an atmosphere, actually a denser one even than Titan’s, and like Titan, liquids on its surface. Due to the lower gravity, the appearance of Titan’s lakes and rivers is somewhat different to Earth’s. For instance, the lakes seem to be more “spidery” in appearance, as if they have fjords. Liquid methane also appears to be more viscous than water, which combined with the much lower gravity would lead to more slowly moving rivers and less response to winds. The waves would also be different. The most important difference between methane and water, and in fact between most other liquids and water, is that the latter expands and therefore floats when it freezes whereas the former doesn’t. This means that freezing lakes on Titan would solidify from the bottom upward, making them less liable to melting or insulation from ice. Water is also slightly blue, but methane is almost perfectly colourless, so even without the distinctly orange lighting of the surface there would not be the usual bluish vista of the sea on this moon, but it is very slightly green. It’s also got a slightly lower refractive index than water, which would have some influence on the apparent distance to the horizon in humid air. However, that’s pure methane and the seas of Titan are not pure.

On Earth, we have two kinds of water. Most of our water is salty because it’s dissolved minerals from the sea bed and elsewhere, but when it first lands on the surface as snow, rain, hail, dew or frost it’s fresh. A similar division exists on Titan. The large standing bodies of water have had time to dissolve ethane and are in fact solutions of ethane in methane. They are also blackened by other hydrocarbn impurities dissolved from the crust into them. I’m guessing that this means there are “tar flats” there like Earth’s salt flats, and also the equivalent of hypersaline lakes but with ethane instead of salt.

Titan’s appearance from space is vivid orange because of the photochemical smog, similar to the reddish tholins found on many small objects far from the Sun, and they are in fact tholins themselves. In the case of the moon, it’s actually possible to image the horizon and the changing colours of the atmosphere from orbit like it is with Earth:

This is actually an ultraviolet image but has been colourised to resemble what would be seen by the human eye. Leaving its air’s composition and density aside for a bit, Titan is an important model for how an atmosphere behaves on a cold, fairly uniformly heated and slowly rotating spheroidal body. This came up recently in discussions I had with flat Earthers, because they attempt to explain the movement of Earth’s atmosphere based on the assumption that it doesn’t rotate and try to find another model which doesn’t use the Coriolis Effect. Titan and Venus provide such a model, and theoretical simulation of this moon’s atmosphere doesn’t rely on its actual existence. Like many moons, Titan has captured rotation and always shows the same face to Saturn during its sixteen day orbit, giving it a sixteen-day rotation. On a world much closer to the Sun, such a slow day would lead to winds in the atmosphere being dominated by the temperature differential between the night side and the subsolar point, leading to an “eyeball planet” to some extent, although unlike a genuine such planet it would still be rotating a little. There would be winds blowing from the tropics on the day side towards all parts of the night side, radially arranged. Above Titan, the atmosphere develops similar bands to what’s found on Jupiter, although they’re not visually apparent due to the relative homogeneity of the atmosphere. There are basically longitudinally-oriented rings around the planet with convection currents circulating between higher and lower altitudes and preventing mixing between latitudes. This is very indirect evidence that Earth is round, because if our planet wasn’t spinning this is how our atmosphere would behave, ignoring heat sources, and it doesn’t. In fact I wonder if that also causes the distinctive layers in this image. Perhaps there are multiple rotating “tubes” of air which don’t interact with each other.

The atmosphere is not horizontally homogenous. There is a “polar hood”. Titan’s orbit adds about twenty minutes to Saturn’s axial tilt of 27°, meaning that both have seasons, but in Titan’s case there is little or no significant internal heat influencing the weather, so Titan would exhibit seasons around seven years long each. The polar hood is a dark zone around the pole extending quite some way towards the equator, 70°, which appears in the local winter. It appears over both poles at different times of the “year”, i.e. the thirty-year period of Saturn’s and therefore Titan’s trip around the Sun. It seems to be caused by down-welling, which is the tendency for haze to build up in the winter at high altitudes which is then transported to the other hemisphere during spring.

Due to the lower gravity, the atmosphere is much deeper (or higher) than ours. Our “scale height”, the altitude over which density decreases by a factor of ε, or roughly 2.718. . . , is around eight and a half kilometres. The Titanean scale height is from fifteen to fifty kilometres. Now might be a good time to talk about scale height in more detail. It’s common knowledge that the further up you go on Earth, the thinner the air is. Most people cannot breathe at the top of Mount Everest without help although one can acclimatise oneself, and the air pressure inside an airliner is noticeably lower than at sea level, although it is also somewhat pressurised. The Kármán Line is the official boundary between Earth’s atmosphere and space, but is no more “real” than the borders between countries. It’s a hundred kilometres above sea level. However, the atmosphere doesn’t just suddenly cut off at that height, but gradually fades out. However, it doesn’t do that in a linear fashion. The air pressure 8.5 kilometres up is around 370 millibars, and at seventeen kilometres it’s 135 millibars, i.e. 2.718 times lower. At the Kármán line it’s about eight microbars. This actually means that were it not for the low temperature and lack of oxygen, it would be possible to survive at a much greater altitude above Titan than above Earth. The Armstrong Limit is the height at which the boiling point of water is equivalent to human body temperature, and the pressure is 62 millibars. This is about eighteen or nineteen kilometres above sea level. On Titan, taking the higher sea level (!) pressure of the atmosphere into consideration, this occurs at a minimum altitude of almost fifty kilometres up, which on Earth is the maximum height a balloon can rise to before pressure within it is equivalent to pressure around it, giving it neutral buoyancy. This also means that said balloons, airships etc, could operate at a much greater height above Titan than on Earth, at about a hundred and thirty kilometres, which on Earth would be well into space.

Methane rising into Titan’s upper atmosphere is broken down by radiation into hydrogen and ethane, which is effectively a dimer of methane with a hydrogen atom missing (in other words two methyl groups). Although it might be expected that this hydrogen would leave the atmosphere entirely, and I’m sure a lot does, what mainly happens is that the hydrogen expands and occupies a greater range of heights than it starts off at, and this leads to it moving down into the lower atmosphere. It would usually then be expected to rise back up again and leave, or perhaps react with something else, but in fact it seems to disappear. It’s been suggested that this hydrogen is being used by living organisms lower in the atmosphere. Once again, this series of posts is not supposed to be about life, but it would be weird to ignore it at this point so I think I have to say something about hydrogenosomes.

Cells with nuclei usually contain a number of bodies referred to as plastids. These include chloroplasts and mitochondria. Both of these evolved from independent microörganisms and provide their host cells with functions they would otherwise have to evolve or do themselves. Chloroplasts are of course former blue-green algæ and responsible for the kind of photosynthesis which produces oxygen as a waste product. Mitochondria use this oxygen to release energy from glucose in a controlled manner known as the Krebs Cycle. Hydrogenosomes are similar to mitochondria, are thought to have evolved from them, and do a similar job, but are found in anærobic environments, which is of course what Titan and almost everywhere else in the Universe is. They release energy by converting protons to molecular hydrogen. This is the opposite of what organisms on Titan would be doing with it, but it suggests that there is a potential source of energy there and it would explain why the hydrogen seems to vanish. Chloroplasts and mitochondria effectively have opposite functions, so maybe these are the opposite to hydrogenosomes.

Titan’s surface has now been completely mapped:

Perhaps surprisingly, in spite of the dense atmosphere and liquid and gaseous erosion, there are a number of craters on the surface, although they’re very sparse. These are the red patches on the map, all in the same hemidemisphere. The blue patches are lakes, and it’s notable that they’re within the polar circle, mainly the “Arctic”. Near the equator are dune fields, the purple bits. The green areas, plainly the largest, are in fact plains. Finally, the orange bits are described as “hummocky”. This is a cylindrical projection albedo map:

The impression one gets when looking at Titan is of a planet rather than a mere moon. It doesn’t feel like a mere adjunct to Saturn. This is clearly partly due to its size and mass, but it’s also the presence of a proper atmosphere. With the other moons, some of which technically have atmospheres which consist of sparse atoms and molecules bouncing around and perhaps orbiting, the surfaces are open to space and there’s less sense of “special space” with them. Titan’s not like that, and nor is Earth. Earth’s surface, ocean and atmosphere count to some extent as a “special space”. I will probably explain that in more depth at some point, but the gist is that there are some regions which count as special spaces for us, such as the Holy of Holies, an operating theatre, backstage or the parts of shops customers have no access to. Although they’re continuous with the rest of the Universe, there’s also a sense in which they’re kind of “roped off”, and I get that impression from Titan, but not any other moon. Conceptually it may be linked to liminal spaces and in a contemporary sense the “backrooms”. In a way, the whole of Titan’s surface is a huge “backroom”, since we’re trans its atmosphere and Titan is cis to it. It’s an arduous endeavour to reach sea level here, and it’s also kind of doing its own thing. For instance, it actually does have a sea level, or perhaps a mean sea level, since there seem to be at least two separate systems of liquid bodies. Tides will inevitably occur in these lakes, raised by Saturn and the other moons to some extent, and will be higher than is obvious due to the lower gravity. In a way, Titan is also a “desert world”, since although it does have bodies of methane on its surface they don’t form an extensive ocean. Perhaps somewhere out there are moons or planets with proper continents and oceans.

The presence of nitrogen in both Titan’s and Earth’s atmospheres suggests something further. Maybe there are planets and moons out there with oceans of liquid nitrogen.

Titan’s surface area is over eighty-three million square kilometres. This is far larger than any country or continent and getting on for the total land surface area of Earth. Next to it, even Rhea is small. It’s larger than Mercury and about the same size as Ganymede. Due to the lakes, its own land surface area is a little under that, and the greatest distance between two points on its surface is just over eight thousand kilometres, which is about the same as London to Los Angeles. This is not just some trivial moon you can give the brush-off to. It’s a massive great hulking world in space, getting on for the size of Mars, but far more distant. Similar colours too. Unlike Mars, however, Titan is constantly active and busy, with probable volcanic eruptions, though not to the extent on Io, but with water instead of lava, mixed with ammonia. It has gullies, branching streams and rivers with tributaries and evidence of tectonic activity. Basically the same stuff happens on Titan as on Earth, geologically, but with different materials involved. That said, although the surface is constantly being remodelled, it does seem that the occasional impact crater can persist. I have to say I don’t understand how.

There is more organic material and more complex organic chemistry going on there than on any other body apart from Earth. I’ve said before that tholins are like organic life’s cousin. It’s like the original complex mess of organic compounds which exist on or in a solid body have two alternatives as to how to develop, one being life and the other tholins. In Titan’s case, tholins have gone further than in any other known situation. the atmosphere is a case in point. On Earth, most of the complex chemistry going on in our atmosphere is in some way linked to life. Apart from that, there’s oxidation, almost completely inert nitrogen and completely inert argon. Lightning can cause nitrogenous compounds to form and ozone forms in the upper atmosphere, but most of what goes on here is physical. The organic chemistry is highly complex but mainly goes on inside organisms. This is not so on Titan, and may well not have been so when Earth was young and less organic material was locked up inside the biosphere, so although it’s much colder and therefore less reactive, Titan may be a passable model for what used to happen here before life evolved.

Broadly, what’s going on in the Titanean atmosphere, which remember is very deep compared to ours and therefore has a lot of stuff in it to react with each other in any case, is similar to what happens over a major polluted city in a hollow on a warm sunny day, one difference being that there’s no industry to inject the stuff into the air. Æons ago, all of the sludge we’ve dredged up with oil rigs and put into the atmosphere and water cycle wasn’t yet incorporated into the bodies of organisms, and may have been in a similar form, so we’re kind of returning our planet to the state it used to be in before life appeared on it, hence the resemblance to Titan. On Earth, vehicle exhausts form nitric oxide, which combines with organic compounds from the likes of paint, glue, weedkiller and other industrial and domestic chemicals along with the secondary pollutant peroxyacetyl nitrate formed from vehicle exhaust and fossil fuel power stations to form nitrogen oxides and ozone at a low level due to the action of sunlight on the chemicals. This turns out to be harmful to air-breathing organisms living in that environment.

The big difference with Titan is that there’s no free oxygen at all, although there is some locked up in compounds, so the process is rather different. It’s said to be possible to explain every detected compound in the atmosphere from the action of sunlight on a mixture of nitrogen and methane, although I don’t understand how because some compounds contain oxygen. Titan’s atmosphere is 94% nitrogen, six percent helium (which does nothing and therefore makes no contribution to the chemistry), 0.01% methane, and also acetylene, ethane, propane, diacetylene, methylacetylene, hydrogen cyanide, cyanoacetylene, cyanogen, carbon dioxide and carbon monoxide. In particular, there are several cyanide-based gases and the similar carbon monoxide, though in small amounts. Cyanogen is quite an interesting gas because it can behave as if it’s a halogen like chlorine or bromine. Several constituents also have nitrile groups, which also exist in superglue and an artificial rubber – I have a box full of nitrile gloves upstairs for the purpose of dealing with certain other organic materials. Although nitriles basically are cyanides, but properly organic as opposed to happening to include a couple of carbon atoms which might as well be any other lightish element, they tend to be a lot less toxic, possibly because the molecules are larger. Hydrogen cyanide in particular is a key intermediate in the synthesis of amino acids. As the chemical reactions proceed, I imagine the compounds get heavier and precipitate out of the sky onto the surface, so there will be substances vaguely resembling synthetic rubbers and glues, among other chemicals, on the ground and in the lakes and rivers, not at pollutants but as part of the uninterfered-with environment. All of this stuff will be in an unholy mess, all being mixed together, and it’s also hard to work out how it will behave at such a low temperature, but once again this is how Titan is the reverse of Earth. On Earth, all the plastic and other stuff is pollution. On Titan it’s a pristine part of the cycle: “natural”, to use that useless word. Deconstructing that word, though, maybe our seas being full of plastic and our air full of extra greenhouse gases is just as natural and it just took a convoluted path between a Titan-like original situation, a few thousand million years of evolution, the emergence of a technological species and a rapid return to Titaneanism.

Life, therefore, rears its head at this juncture. Titan has not one but two chances of being a life-bearing world because of its interior and its surface. There’s a whole load of stuff going on in its atmosphere and seas of course. Complex organic chemistry is a fact of (non-)life on Titan, but there is a problem: there is only rarely liquid water on the surface. It probably does happen, during volcanic eruptions, but the water emerging from these will freeze quickly. I suppose it’s possible that there would be microbes flitting around from site to site in these situations, waiting to take advantage of the brief periods that tiny area of the moon is above freezing, and in a way the combination of salty water and complex organic molecules almost seems to guarantee that life will find a way, but at this point we don’t know if life always happens when it can or if it’s a quadrillion-to-one chance that we exist on this planet, lost in the depths of a lifeless cosmos. But maybe water isn’t necessary to life anyway. Isaac Asimov, who was officially a biochemist, suggested that methane could replace water if instead of protein biochemistry used lipids. The crucial thing about water is its polarity. Water molecules are negatively charged on one side and positively charged on the other, which enables water to be a good solvent and to form cages around enzymes and extend their actions, among other things. This kind of life on Titan would use up molecular hydrogen by combining it with hydrocarbons, which would explain why there’s less hydrogen than expected in the lower atmosphere. And life gets a second bite of the cherry in Titan’s case, because as well as having an active and chemically complex surface, Titan is like many other outer moons in apparently having a hypersaline ocean underneath its icy crust, meaning that organisms could exist there too, with more familiar biochemistry. The mantle is a eutectic mix of water and ammonia, with some carbon dioxide, and is liquid. Immediately above it is a soup or sticky blend of complex organic molecules and the surface is tectonically active, meaning that these chemicals could be pushed into that ocean by movements of the crust and possible plates, if it goes that far. In the meantime, Titan appears to have many partially-assembled substances industries and chemists on Earth have expended considerable efforts in synthesising, such as the aforementioned artificial rubber monomers and components of superglue, as well as immense amounts of the same kind of hydrocarbons we use to power our entire civilisation, and I wonder whether it would be economically viable to fetch them from the moon and bring them back. It wouldn’t be a good thing though, due to the need for a low-carbon economy, but the presence of such compounds and their accessibility could ultimately lead to cheaper “fossil” fuels. Just as an example, the atmosphere contains twenty parts per million of propane. That’s more than seventeen millard tonnes. It’s notable that Russia is this planet’s largest supplier of natural gas. Even so, Titan is a long way away at one and a half light hours on average.

About an eighth of the surface is covered in dunes, which is about the size of the Sahara. This, again, is only possible on a world with a substantial atmosphere and some solid surface because they’re formed by winds. Mars has dunes but I’m not sure about Venus. They’re most similar to those in Namibia, which is where Earth’s highest dunes are, average a hundred metres high and can be hundreds of kilometres long. They give a good indication of the wind direction and are probably large in scale due to the low gravity and it also suggests that there are effectively desert conditions in those regions, emphasising the confusing fact that although Titan has seas, it’s actually a desert world. The dunes are around the tropics and cross the equator, although there are some other patches such as near the northern seas. It was initially speculated that these dark regions, which have a kind of fluid outline, were actually a surface ocean of methane and ethane, and they do flow around higher ground, but it’s actually some kind of organic “sand” being pushed around by the wind. The actual dues themselves are fairly widely separated and also quite steep and narrow themselves, like the dunes in the Namib Desert. It could even be that these grains are effectively plastic granules like those hoisted into hoppers and extruded, and personally I think this would make them suitable building materials.

Also mainly in the tropics is the “hummocky” terrain. Hummocks are small knolls or mounds which on Earth are formed by landslides or in permafrost-rich areas. These cover a further seventh of the world and are made of ice, which is like bedrock on Titan. They’re likely to have formed soon after the body itself and represent wrinkles in a solidifying surface due to contraction through cooling. Again, the hummocks turn up away from the tropics as well and are found in particular in the southern hemisphere.

There are also small regions of “labyrinth terrain”. These are maze-like structures (back to the backrooms?) cut by methane rivers, either through dissolving the surface or physically eroding it, and occur in areas of greater rainfall, often near high ground. On Earth, the Indonesian region of Gunungkidul is similar, consisting of limestone hills riddled with horizontal and vertical caves. The fact that this region on Earth is limestone suggests to me that methane rain may be dissolving the solid surface rather than just eroding it, but I’m no geologist.

The majority of the surface is covered by plains.

The illumination of Titan’s surface during the day is only 1% of Earth’s. This sounds very dim, but in fact it isn’t. Being around ten times Earth’s distance from the Sun, Titan already receives only a hundredth of the sunlight we get per unit area. Nine-tenths even of this is filtered out by the smog. The photo from ground level taken by the Huygens lander gives a fair impression of the murkiness as it would be seen by someone coming out of the kind of sunlight we experience on Earth, but it should also be remembered that the Sun is around sixty thousand times brighter than Cynthia at maximum brightness, so this is like a world with sixty “full moons” in its sky, and nobody could call that dim. The chances are you wouldn’t even notice after a while, although it would be overcast.

There may be clathrate hydrates in the makeup of the crust. These are also present at the bottom of the sea on Earth, and consist of ice which has “imprisoned” methane molecules in its own molecular cages. On Earth, these present a potential major risk of climate change because methane is such a powerful greenhouse gas that it could raise global temperatures catastrophically. On Titan, this is not an issue due to the low temperature.

The crust is around 150 kilometres thick, which makes the kind of missions suggested to Europa’s or Enceladus’s internal oceans less feasible in Titan’s case. Beneath the ocean, the same kind of process may be occurring as is apparent in the depths of Ganymede, with unusual (for us) allotropes of ice such as the cubic form. On the ocean bed there is probably hydroxide “mud” on top of a large rocky globe.

I feel this is such a huge and involved subject that although there’s still a lot I haven’t covered, some of which is very important, I’m going to stop here. Just be aware that Titan is in some ways as sophisticated and complex as Earth and is far more than just another moon.

Next time, the very different and much smaller Hyperion.

A Post-Truth Test Tube

I’m currently a recovering addict. A few months ago on a whim I joined a FB group to debate Earth’s shape. I’ve come across flat Earthers before, online at least. Whether I’ve encountered adult Westerners who believe Earth is flat, I don’t know. Finding the group highly addictive, I became one of the main posters and enjoyed it a lot, but it isn’t really the best employment of one’s time. That said, it does constitute an interesting case study of the way we think and behave.

The useful thing about looking at flat Earther psychology is that it’s firmly established that Earth is spheroidal. The room for doubt is practically submicroscopic on this matter, so there’s no risk of being wrong or being drawn into believing that it’s flat, and because of that, rather than becoming embroiled in arguments which might persuade one, one can instead just examine how flat Earthers justify their position. Positions plural, actually. Most flat Earthers seem to believe we are on an almost flat surface under a transparent dome with the Sun going round us, but there are other views. For instance, some believe Earth as we know it is surrounded by broader rings of continents and oceans to which we have no access, and to be honest that is a really fascinating and appealing view which might go some way towards addressing the claustrophobia of the more restricted version, and a few of them seem to believe we are on an infinite plane. I say “seem to” because this is one of the problems with trying to work out what’s pagoing on: are they serious about this or just kidding around?

The answer to this is probably that it depends. This is one thing about groups seen from a distance as opposed to groups examined more closely: the details of individual differences become clearer. As far as I can tell, there seem to be several categories of “flat Earther”. There certainly are people who are just joking, and in fact when the flat Earth society was reëstablished in I think the ‘noughties, it appears to have been a joke. There are also trolls, which is a slightly different thing because I suspect the people concerned enjoy either tweaking the feathers of people they see as nerds or deceiving people into thinking it’s flat for fun. This seems to blend into a group of people who are trying to make money out of gullible people and present themselves as serious campaigners and investigators on the issue. Then there are their followers, who have bought into the whole thing, which is where the conspiracy theories start. There are few people who think independently on the issue, and there are then religiously-motivated people and people who are simply persuaded but not particularly religious. Finally, there are enquiring people who don’t seem to be skilled at fact-checking and simply feel that the two views, flat and round Earth, are equally open to question: kind of “false balance” people who think there is enough evidence for it to be a fair fight.

I can certainly vouch for the power of the force of gravity here, because I couldn’t leave it alone. Rather than manifesting itself as concluding Earth was flat for me, it came across as a compulsion to post and address issues even though I knew it wouldn’t persuade anyone to do it. It may be worth asking myself questions about why I felt the draw of the belief system and attempting to change it, and why “flat Eartherism” in particular has this pull. I know that I have obsessive-compulsive tendencies although I’m not going to pathologise that or embrace a self-diagnosis, but it is there and it probably is a factor for me. But it was also very time-consuming. Cutting my ties with it is also a judgement call, because it’s possible for some people actually to make a living out of addressing the issue. There are, for example, YouTube channels devoted to debunking flat Eartherism as well as all the so-called “Truth” channels focussing on promoting it. Pushing it far enough might in theory have brought some money in although I’m small fry in that pond,so probably not.

This raises the question of whether it’s harmless. In a way, this is beside the point. It’s more that the occurrence of the belief, which often seems to be a long way down the line for many people who have come to question other widely-held beliefs such as how genuine the Apollo program was, is symptomatic of poor fact-checking abilities, and when I say “ability” I do believe critical thinking can be developed in most people. They could even develop it themselves, although it may be difficult to overcome emotional and social attachment to a belief. It is also true that believing Earth is flat is going to exclude people from certain lines of work, or at least make it difficult for them to pursue them, such as on large engineering projects or piloting international aircraft, so maybe human resources are lost to society because of this belief. More broadly, however, there are the issues of overvalued ideas, vulnerability to more negative consequences from other beliefs (anti-vaccination comes to mind) and the general feeling of distrust and fear which may arise from the idea that there is a vast conspiracy to keep all this from the public. The size of this effort would be a lot bigger in this case than any other conspiracy I can think of, because so much more depends on the shape of the planet than other things.

Looking at the trolls, and here I presume that trolls exist and I’d expect there to be at least a few, an outsider would see them as pretending to be of low intelligence and poorly-educated, which is an odd thing to do to one’s reputation. I imagine that they are deriving entertainment from successfully deceiving others or annoying people they may see as nerds. I have in common with these people that I’m drawn into wasting my time and energy on a project which is not very productive and a bit of a pointless endeavour. Trolling is something I don’t fully understand and I sometimes wonder if trolls even know what their real motivations are, because it’s so easy to develop an online persona unintentionally. Beyond this, I can even develop a little conspiracy hypothesis of my own that the whole exercise is a distraction from more consequential issues for all of us, not just the flat Earthers. It’s possible to drop the whole intentional fallacy from this idea and just say, this is what it does and it doesn’t matter if it’s a concerted effort or not. This is one reason why I’ve given up on them, because it really is a bit of a waste of time.

There’s also something like the “sunk cost fallacy” operating here, perhaps on both sides. The sunk cost fallacy is the feeling that because you’ve spent a lot of time and resources, and have perhaps lost a lot in your own life socially and otherwise by pursuing a particular goal, it’s hard to back out of it. If you’ve become a flat Earther, you may value the comradeship of the people around you, online or off, and in many sallies away from majority opinion, people can lose friends and acquaintances, and also opportunities, and all of these things amount to costs. Another form of cost is the embarrassment one may experience from admitting one was wrong.

All that said, we should avoid “othering” people whose beliefs we’re confident are incorrect. One reason for this is that having delusions is part of the healthy human psyche, and even where they don’t serve a positive purpose they may nonetheless exist. Failure to acknowledge that we rationalise our beliefs, even if they’re correct and well-supported by evidence, is lack of self-awareness. Our beliefs also have functions beyond the practical. They can be like interests which bind a club together, and of course this is a substantial part of the function of religious beliefs. I have long maintained that religious belief of some kind is inevitable and therefore that we shouldn’t always resist it, as it can play a valuable part in maintaining good mental health. The question here is whether believing Earth is flat is worthwhile enough for the cost paid through lack of contact with reality.

I have an acquaintance who used to be quite a close family friend. We even went on holiday together and attempted some joint business ventures. Quite some time back, they expressed the view that the Apollo missions were a hoax. I engaged with them on this but they didn’t change their mind. I should point out at this stage that this person was a faithful Green Party voter and possibly even a member of the party. They were also an alternative medicine practitioner. This particular category of work has a lot of variation in it and can be stigmatised. It’s also how many people see me. Nonetheless there is a perceived issue of evidence supporting efficaciousness or otherwise which plainly does apply to some modalities. During the lockdown, they expressed support for Trump, not just regarding his approach to the pandemic but more widely. I could make a link between belief that Apollo was a hoax and this later conclusion. I found the incident very saddening and disappointing.

It seems that a lot of the more vocal flat Earthers nowadays connect their beliefs to the Apollo hoax idea, which makes sense if you think Earth is flat, and also to anthropogenic climate change denial, the New World Order conspiracy theory and anti-vaccination. Of all of these, I should point out that in the 1990s I was close to being anti-vaxx, although my problem was that as usual my opinion wasn’t similar to that of others. I tended to get lumped in with anti-vaxx people even though my actual position was that I wanted some vaccinations to be given by inhaler or nebuliser, not injection, rather than being opposed to vaccinations as such, and as such wasn’t opposed to the single tetanus jab or OPV per se. Now that this is being done routinely with children, I no longer have that objection although I am still concerned about the evolution of slow viruses by attenuation. However, I’ve long felt that the real problem with vaccination resistance is that much of the population doesn’t feel respected or listened to, and I wonder also if this is a factor here. This is one conspiracy theory I’ve seen from the inside. I get the impression also that flat Eartherism is the “hard drug” as it were. It’s the last thing people end up believing in once they’ve accepted all the others.

Due to the universal nature of delusions, a more useful marker for mental illness may be the overvalued idea. It isn’t so much that people believe Earth is flat as that they’re preoccupied with the idea and it comes to dominate their lives. It is understandable that if you think something so fundamental is different than how it’s presented publicly, you probably would think it was quite important to do something about it, and are also likely to think there may be a sinister reason behind the deception. Is it an overvalued idea for a starving person to focus on finding something to eat?

According to the conspiracy theory, the rationale behind persuading the world that Earth is round is to dislodge humans from the centre of creation and lose Earth in the vastness of an impersonal Universe, thereby undermining theism. If that were the aim, it seems like overkill. Why would it be necessary to keep “building” the Universe in the way they would have had to have been doing, for instance initially portraying distant galaxies as nebulæ within our own and likewise with quasars, before promoting them to enormous distances? There’s another perspective within this one that the Big Bang theory, evolution and flat Earthism are all part of a plot to do this, and are associated with the Illuminati, the Masons and unfortunately sometimes the Jews. This last association probably indicates why all this might be dangerous.

I actually find the bog-standard flat Earther view to be claustrophobic and think it makes the world feel like a prison. It also seems to guarantee that there is no life anywhere except on Earth, which for me is a deal-breaker for theistic prayer and worship. If God chooses to sustain a Universe where we are the only sentient beings in a single biosphere, it seems like God cannot be related to by humans on an emotional level. This makes more sense if one does see the Universe as vast, but it still works to some extent on the prison world hypothesis because whereas God could have chosen to sustain a vast Universe, she chose not to, which means we’re trapped conceptually. Of course, we could still be literally trapped on Earth in a vast Universe, but at least the way things are we do know how enormous the world is and the contrast with the largely lifeless Universe in which we’re embedded emphasises the specialness of this planet. This would be less true of an infinite plane Universe though there is still the problem of apparently being at its centre, since it is supposed to be infinite and therefore has either no centre or a ubiquitous one.

Of course one might be forgiven for asking why this matters given the current world situation, and that’s a valid question. It would be easy to come up with a conspiracy theory of one’s own here, that fine minds are being distracted from what matters in order that atrocities can be committed, but in response to that I would say that many of the minds which are being distracted, mine included, are rather far from fine and wouldn’t make much of a contribution anyway, and also that it’s a basic principle to focus on the consequences of a set of circumstances more than the cause, which is a distraction in itself and also symptomatic rather than the more general underlying cause of the problem, which would be worth addressing. The question remains, then, of whether one should bother with this at all. Unfortunately the answer seems to be yes, because analysis of how the issue has arisen allows insight into how other more serious issues have, or might do in future. It’s a kind of model for how, for example, Russian trolls might influence voting in elections or how the Rohingya genocide was engineered.

The idea of conspiracy has tended to centre on NASA as a major actor in this realm. This is peculiar as the sphericality of the planet seems to have been first suggested by Pythagoras in the sixth century BCE, its circumference measured by Eratosthenes in the third century BCE and it was then accepted by the Church into the European Middle Ages, to the extent that they used to discuss whether it was possible that God would have created land on the opposite side of the globe from Christendom because if it were inhabited, it might not be feasible for the Word of God to reach them. I have to admit to being a little confused by this as it seems to imply their view of gravity was quite modern, but it is nonetheless so.

This does, however, raise the question of what kinds of people accepted Earth as round at the time. It does seem quite likely that the average European peasant would not have had an explicit view of Earth’s shape at the time, as they had more pressing concerns, but that might be to underestimate their mentality. Likewise, it also seems entirely feasible that even today many peoples who have not had contact with Western civilisation would assume Earth is flat. The rather startling figure of seven percent of Brazilians, though, appears to refer to Europeanised Brazilians rather than the likes of the Yanomami.

I’ve noticed also that some flat Earthers are merely repeating claims without checking up on them. Two of these in particular are that until the 1920s, US public schools taught that the world was flat. This does not tally well with discoverable facts about history. It was the work of a couple of minutes to locate a digital archive of nineteenth century school geography textbooks, on whose first page it was stated categorically that Earth is round and we live on its exterior. This particular work was published in 1889. It is possible that children were being taught that the world was flat at a later date, for a couple of reasons. One is that teachers don’t necessarily teach what is on the curriculum, and could be either poorly educated themselves or believe that it’s flat, in which case they would presumably teach that if the issue arose. Another is that it isn’t clear how far such textbooks had penetrated by this time. A second, less consequential, claim is that Eratosthenes was inserted into textbooks in the 1980s. I am in the happy position of being able to refute this. I first read of his experiment in ‘The Collins New World Of Knowledge Encyclopedia Of Science And Technology’, published I think in 1973. It’s quite an audacious claim that it was added more recently than that, and I expect that if I were to bother to look, I would find earlier examples. These two claims make me feel that it’s almost Last Thursdayism. A rather similar claim is that NASA pictures taken in the 1960s are CGI, which is very peculiar as there would’ve been many other ways to fake images at that time.

Getting back to NASA, there are two oddities about this particular focus. One is that their existence is completely superfluous to the evidence Earth is round, which as I said is millennia old. Another is that they are only one of many space agencies, which I think probably reflects the US-centric nature of Flat Earthism. There are around sixteen space agencies with launch capability and several times that number capable of doing things like building satellites to be launched by others. These two aspects seem to reveal a considerable degree of ignorance about general knowledge. This is coupled with two other aspects of how flat Earthers view education. They often view mathematics with suspicion and are unwilling to apply the scientific method, often engaging in ad hominem attacks when these are used. All of this taken together had led me to feel that they have been poorly served by the schooling system. They seem to regard belief in a round Earth to result from indoctrination when well-expressed scientifically based tests which are easily reproduced by someone without elaborate equipment are actively avoided. This makes it more likely that their beliefs are motivated by religious sensibilities, but unfortunately not open-minded or progressive ones.

The Bible does seem to imply that its human writers tended to assume Earth was flat. Apart from references to “the four corners of the Earth” in the Tanakh, Jesus is depicted as rising into heaven above Earth, which suggests a sandwich-like cosmology with heaven constituting an entirely horizontal layer above the terrestrial realm. It also raises a question in my mind which I’ve been unable to answer so far. If Biblically literalist Christians (and also many Muslims but not religious Jews on the whole) are often young Earth creationists due to their approach to their sacred texts, why is it less common for them to be flat Earthers? Such a view is clearly assumed by Biblical authors just as creationism is, yet the view is much less popular. If I could crack this conundrum, it might lead me towards better arguments against creationism. This might also be a massive waste of time of course, like the rest of it.

A major problem with how flat Earthers interact with the rest of humanity is that we who have an accurate view of Earth’s shape are often guilty of ridicule and insult towards them. This leads to entrenched positions which are defended and attacked not by reasoned argument but through largely emotional interaction. I can imagine a flat Earther becoming more relaxed about her beliefs and getting on with her lives in other ways, and then eventually not caring much about Earth’s shape or quietly conceding she was wrong, but if that day does dawn in their lives, it will do so a lot later if they’ve been pummeled for their beliefs in this way. They’re likely to thrive on persecution, and it is in any case wrong to behave thusly towards them. This may fuel the retention of the beliefs in question.

Flat Earthers, oddly, seem to see the rest of us as indoctrinated “sheeple”. Both sides seem to accuse the other of the same things, and for once because we are able to state confidently that Earth is not flat and back that up with evidence, it’s possible to separate the accusations from the reality, but it is still interesting that they perceive us as we perceive them. Unlike us, sadly in a way, the evidence they present is not remotely convincing and could only be believed by someone who was both unaware of science in the sense of it being a body of information and of the scientific method. They often think of scientists as having their views dictated by monetary interests, and to be honest this has been known to happen, as with medical research into the consequences of smoking tobacco, but in the case of investigating Earth’s shape this is easily reproducible. I have, as mentioned here before, suggested that in order to avoid accusations of manipulation, they come up with their own falsifiable test but I have never known one to do that.

It only takes one reliable falsification for a hypothesis to be rejected. In the case of Earth being flat, many falsifications are available. It would be interesting if the hypothesis that Earth is round could be falsified, but apart from minor details such as its oblateness this has not happened so far and nothing offered by flat Earthers that I’m aware of has succeeded in doing so. Good quality evidence would be most welcome, but is not forthcoming. The closest they get is objects being visible which seem to be beyond the line of sight, but when this is definitely testable it can be explained by refraction of light by the atmosphere, which can only make objects appear higher, i.e. visible if somewhat beyond the horizon, than they would be if no atmosphere was present. Other, similar attempts have been made, such as the claim that RADAR works beyond the horizon. It does, but that’s a special kind of RADAR called, appropriately, “over the horizon RADAR” and works by bouncing short wave radio waves off the ionosphere. Similarly, a microwave mast in Cyprus can communicate with one in the Lebanon, and since microwaves only work by line of sight this would only be possible if each is above the horizon from the other’s perspective, but in fact Lebanon is quite a mountainous country and this is not at all problematic.

I’ve also noticed quite basic misunderstandings which seem to result from not reading sources closely. One flat Earther claimed that my own claim that seismic waves indicated that there was an apparently spheroidal core centred six thousand odd kilometres below the surface was outdated because Earth’s core was not made of iron and nickel but of ionised light elements such as hydrogen and oxygen, and provided a link. What they actually linked to, if followed, reveals a paper which was scientifically quite rigorous but didn’t make this claim. Rather, it claimed that seismic waves appeared to show that Earth’s core was an alloy of iron and nickel combined with ionised hydrogen and oxygen which behaved differently due to the high pressure. This particular flat Earther said they were an ex-engineer who had accepted all their life that the planet was round, but changed their mind later on. Although I’m not questioning that, I do wonder if it’s a sign of cognitive decline, because the paper did not claim anything like they said it did. There were also many spelling mistakes not similar to autocomplete errors in their writing, which again doesn’t show for sure that they’re mistaken but does suggest something regarding their reliability.

All of this, then, seems to be the consequence of something characteristic of our time, perhaps like the Targeted Individual community, where people diagnosable as in a markèdly delusional condition meet others online who reinforce their beliefs of persecution, but combined with poor educational attainment and critical thinking skills. However, we can’t feel all superior about this because not only is it partly about bad luck with the education system, but it’s also nothing more than a delusion we happen not to share, unlike the individual delusions the rest of us happen to have.

If you’re a flat Earther reading this, I want to say the following to you. Although you’re wrong, I will also inevitably be wrong about some of my beliefs, and the reason you’re wrong is not connected to you being in the minority. Even if only a single person in the world believes something, the mere fact that it’s just the one person has no bearing on whether it’s true or not. I don’t want you to feel I treat you with contempt, and if any of what I’ve written has made you feel this way, I sincerely apologise. It takes courage to stick to a belief which the whole world is against, and I respect you for that. Who knows what else we might have in common outside this area?

An Ocean, A Moon And A Giant

Tethys on this blog has mostly been used to refer to the ancient ocean which used to run between the southern and northern continental blocks of Gondwanaland and Laurasia, which finally closed when the Mediterranean formed, all that’s left of it today really, and North and South America collided. Up until that point, an ocean had run right round the world, a little like the Southern Ocean today but near the tropics, which therefore had a powerful circular current and perhaps also strong winds. It would’ve allowed sail boats to navigate and travel quite easily around the planet, so in a way it’s a shame it ceased to be while we were still living in the trees, but maybe not.

The reason it was called Tethys stems from the fact that today’s Atlantic Ocean was named after the titan Atlas. Tethys the titan married her brother Okeanos, who was a vast river encircling the world. Tethys herself, although a mythical figure, has hardly any mythology attached to her. She’s more like Britannia, a mere symbol, in this case for the sea, and there is a further ancient ocean named after her brother Iapetus. She’s also the mother of the sea nymphs, the Oceanids, and numerous river deities. It’s a shame she didn’t do anything really.

The moons of Saturn are of course often named after titans, apart from the one which is actually called Titan, which is a bit weird really, but then most people call Cynthia (Selene, Diana, Artemis) “the Moon”, so Earth’s not much better. Tethys the moon is the innermost large moon of Saturn with a diameter of 1 050 kilometres, and is the second brightest moon per unit area after Enceladus. It’s also practically a twin of the next moon out, Dione, in terms of size. Both moons are in similar orbital resonance relationships with Mimas and Enceladus respectively, which needs some explaining because Mimas is quiet and cold inside whereas Iapetus is quite active and heated, apparently by tidal forces from Dione. Tethys is accompanied in its orbit by two trojan moons each forming the points of an equilateral triangle with it and Saturn, called Telesto and Calypso, Telesto being the leading member of the pair. Calypso is slightly larger but both are roughly the size of the Isle of Wight. Remarkably, even though both were discovered in 1980, it wasn’t the Voyager probes what did it, but telescopes on Earth. They were originally known as Tethys B and C. I didn’t know about them at the time, although I did know about Dione B, which is another story.

As befits a moon in orbital resonance with Mimas, Tethys too has a proportionately enormous impact basin. Since it’s more than twice the diameter of the inner moon, Odysseus, the crater, is itself four hundred kilometres in diameter, which is larger than the whole of Mimas and forty percent of the diameter of Tethys, making it proportionately the biggest crater that actually still looks like one on any moon. Unlike Herschel on Mimas, the floor of the crater does conform to the spheroidal shape of the moon, meaning that it has little influence on the distance to the horizon. The floor is three kilometres below the mean radius and the rim five kilometres above it, making the edge of the crater almost as high as Mount Everest above sea level, except that in the case of the mountain it rises from a plateau and would therefore not appear to be anything like as high. Nepal is on average already three kilometres above sea level. Moreover, this is a ring around 1 260 kilometres in circumference. In the centre of the crater is a plateau called Scheria Montes around three kilometres high with a basin in its own centre. There are faults around the rim, of which the largest is called Ogygia Chasma.

Even though the proportions of the craters to the moons are similar in both cases, it’s not Tethys but Mimas which has been called the Death Star Moon. This is because Herschel on the latter is relatively speaking a deeper dent than Odysseus. When I first came across Tethys, I’d just been impressed by Herschel’s size, so I was amazed that this second crater was bigger than the whole of Mimas and it is initially puzzling that it’s Mimas which gets all the kudos, but the reason is that Odysseus is smoother and flatter. However, Herschel is centred on the Mimantean equator whereas Odysseus is centred at around 35° north, so it’s actually off-centre in the same way as the Death Star’s depression is. It’s thought that when the crater originally formed, it was deeper but the relative softness of the surface and the higher gravity led to it being smoothed out as the millennia went by. The surface gravity on Mimas is 0.6% of Earth’s, whereas that of Tethys is more than twice that at 1.4%.

Although the gravity is greater, it was formerly thought that the crack across the middle of Tethys was a sign that the entire moon had been shattered by the impact and had fallen back together again. This is known as Ithaca Chasma, and at this point readers of the Iliad and Odyssey will have detected a theme to the names of the features: others include Polyphemus, Ajax, Circe and Penelope. Ithaca probably looks something like this:

Ithaca stretches three-quarters of the way around the world at 2 000 kilometres and is situated at a great circle centred on Odysseus and crossing both poles, interrupted by the crater Telemachus, so it might be thought that it’s connected to the giant crater, but remarkably it’s been found to be coincidental. The relative ages of features on many bodies with little to no atmosphere can be estimated by how cratered they are, and by this method Odysseus has been established to be younger than Ithaca. It was there already. I find this quite a remarkable coincidence, but a crater of that size seems to stand quite a good chance of being aligned with such a feature due to its large size. It’s 20° from the centre of the circle outlined by the chasm, and allowing for that on the surface means it would either be in the hemisphere on one side or the other of the moon from it, which doubles the probability, and allowing for 20° means the area which could be seen as the centre of the circle actually covers sixty degrees of 180, raising the probability to more than one in ten, and there are more than ten round moons orbiting Saturn so it becomes a lot less noteworthy that way. It’s an interesting demonstration of how misleading intuition regarding probability can be.

The chasm is about three kilometres deep and up to a hundred wide, though it varies a lot down to just a few kilometres. It seems to have been caused by the expansion of ice on freezing when the internal ocean froze early in the history of the moon, although it might have resulted from early tidal heating from Dione, which is in 3:2 orbital resonance with it.

The fourth-largest crater is called Penelope, and is just north of the equator about a third of the way across the globe from Odysseus, and has a diameter of two hundred kilometres. It was the second largest known crater before the whole of Tethys was mapped. It’s named after the wife of Odysseus. Away from these two craters, the terrain is quite heavily cratered with an alignment parallel to Ithaca.

It’s Enceladus which makes Tethys so bright. Ice from the geysers on the other moon hit the surface, covering it in very bright material, particularly on the leading side, which is around 12% brighter. The darker hemisphere is about the same colour as the darker of Saturn’s moons and may be high in iron. There are likely to be other constituents than water ice on or near the surface but these are hidden by the ice and so it’s difficult to tell what else is there. The regolith, i.e. the “soil”, actually ice, on Tethys, is unusual in that it’s 95% empty, kind of like polystyrene foam, a situation I imagine is helped by the low gravity and caused by the steady deposition of small particles of ice gently resting on each other over millions of years.

The moon is slightly redder and brighter near the centre of the leading hemisphere, bluer around Ithaca and somewhat darker red on the other side.

That’s about all I have to say about Tethys, which is incidentally about the same size as Ceres but otherwise quite different, being much icier. Next time, Dione.