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.
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.
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?
What’s in a name? If you’ve been following this series, you probably have a good idea which planet comes next. I’ve done Saturn, its moons and the centaurs between Saturn and the next planet, so you will be aware that this leaves me with little choice but to post on the seventh planet of the Solar System, and the first one to be discovered since the invention of the telescope. We all know what its official name is, and how annoying that is.
I’ve already insisted on calling the large satellite which orbits Earth on which astronauts landed at the end of the 1960s CE and into the ’70s, which tends to light up our nights and occasionally covers the Sun almost perfectly, Cynthia. There were other choices, some of which may even have been better. I personally like Selene for example. In fact in that case there were so many choices that it was hard to make a decision. This is unsurprising, since any sighted person would be familiar with the body in question. Not so with this other planet, although intriguingly it is visible to the naked eye on occasion and in days of yore, perhaps even in the Palæozoic, it would’ve been clearly visible to many animals, so the usual statement that it was first discovered on 13th March 1781 is quite anthropocentric in a way. This opens up another much more remote possibility: were humans the first culturally-oriented entities to notice it, or did some starship come by back in the Proterozoic or something, and note its presence? The reason I mention this is that this planet is unusually afflicted by its current official name, and for us this is very significant.
The initial choice wasn’t much better. William Herschel chose to call it Georgium Sidus – “George’s Star” – after King George III. Today this seems like a weird thing to do and it took almost six dozen years for today’s name to be accepted. Garbled internet lore has it that it was called “George”, but this isn’t actually so. There were also a number of other names, but Herschel naming it after his patron seems divisive and not conducive to international coöperation in science. Then again, Virginia was named after Queen Elizabeth and so forth, so it was common practice during that long period of history, and there are also the Sidera Lodoicea.
There were other suggestions. One was actually “Neptune”! This was surreptitiously to celebrate British sea power, so maybe it is just as well that didn’t happen. Another possibility considered was “Oceanus”. Both of these refer to its green-blue colour as well as other things. Being the first historical instance of a planet being discovered, there seems to be an element of what TV tropes calls “Early Installment Weirdness” about the naming. People didn’t have a proper precedent as to what to do about a novel astronomical discovery of this kind. It was initially supposed to be a comet, since these had been encountered before. The moons of Jupiter and Saturn had established a precedent for naming after Greek mythical figures, and this was eventually followed. The planet was dubbed “Uranus”.
There seems to have been a long period in history during which names which are regarded as embarrassing and silly nowadays just weren’t. This applies in particular to surnames and this doesn’t even seem to depend on semantic drift. Whereas I can easily believe that a surname such as Pratt has only become potentially embarrassing recently, there are other names whose pedigree of ridiculousness must be much longer. I should point out here that my own surname is annoying and ridiculous in an English-speaking context, so maybe this has led to me focussing a lot more on this planet’s name than usual. It does seem to suggest that people’s senses of humour, if this can be regarded as more than puerile, change as time goes by. Just to state very clearly what the issue is, there are two ways of pronouncing “Uranus” in English. One is the older pronunciation of “your anus”, which I probably used up until about 1980, and the other, which initially seemed better, has turned out to be heard as “urine-us”. So you can’t win. One way or the other it’s gonna sound stoopid.
It might be thought that this doesn’t really matter. However, imagine you’re a NASA employee or an astronomer going up before some kind of board or committee holding the purse-strings and asking non-specialists, or just non-astronomers, for funding into a mission or research into this planet. One might hope that this would have no bearing on the success of such a bid, but it’s alleged that in fact there is less funding and focus on the planet than might be expected, and if that’s so, the name may not be free of consequences. Or, it could be that the planet and its moons are just harder to reach or less interesting than the other planets and moons. Jupiter and Saturn may be grabbing attention though, and this in itself could be connected to naming.
This planet is the first to be given a Greek rather than a Latin name in international nomenclature. In languages which use Chinese characters it’s known as 天王星, “sky king star”. This actually has the word “wang” in it in Mandarin, but unsurprisingly this is not a double entendre in that language, at least for what it is in English.
It doesn’t end there, although the next bit is a little less well-known. On the whole, moons, planets and asteroids within the system had been named from Greco-Roman mythology. This is quite questionable in some ways but typical of Eurocentric culture, and it extends to much international technical vocabulary, in the sciences and elsewhere. Steps have now been taken to name more recently-discovered objects in other ways, for instance from Inuit, Shinto and Norse traditions among others. Hence, for instance, ʻOumuamua and Sedna. Oddly, the moons of the seventh planet were an early example of a break with tradition which occurred nowhere else for quite some time although it was still Eurocentric. None of the moons have names primarily from European classical mythology, and they never have had, although many are Latinate in form. Instead, they’re mainly named after characters from the works of Shakespeare and Alexander Pope. The first two discoveries, by Herschel himself, are Titania and Oberon. Of these, the first is, I think, a poor choice, partly because it’s too similar to Titan and the associated adjective is Titanian, which many might confuse with the one for Titan, and partly because it tends to be pronounced in all sorts of weird ways such as “tittan-EYE-a”. Once that precedent had been set, two more moons were discovered in 1851 by Lassell – Ariel and Umbriel. Umbriel is, so far as I can tell, the odd one out name-wise, since it’s named after the “dusky sprite” in Pope’s ‘The Rape Of The Lock’. Kuiper continued the tradition in 1948 with Miranda. These are all the relatively large spheroidal moons. Voyager 2 then discovered ten more in 1985-6 when it visited the planet. By that time, Voyager 1 had manœuvred itself around Titan to get a better look and had left the ecliptic, so it would have no more planetary encounters, so it was entirely down to Voyager 2. These moons are named Puck (the sole moon discovered in ’85), Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind and Belinda. These were followed by Caliban and Sycorax in ’97, then one more moon from Voyager data two years later known as Perdita. The remaining moons are called Setebos, Stephano, Prospero, Trinculo, Cupid, Mab, Margaret, Francisco and Ferdinand. Not being an Eng Lit bod, I only recognise some of these names from Shakespeare but Sarada assures me that all of them but Umbriel are Shakespearean.
This, then, provokes a further couple of suggestions regarding the name of this planet. It still draws from European culture, but it also circumvents the “urine/anus” problem. It seems to me there are two possibly appropriate choices for Uranus here. One is to call it Shakespeare. This is problematic in that it’s then an entire planet named after a real person. The other, also a real person but fictionalised by Shakespeare, is to call it Hamlet, in which case it would go back to being named after a royal, based on the Scandinavian legend of Amlóði. This figure may or may not be historical. Hence this is my proposal, and by the way I probably won’t even follow it myself: change the name of Uranus to Hamlet. This would, so far as I can tell, completely solve the silly name problem, and I can well imagine someone sitting down in front of a board of some description and proposing a mission to Hamlet without a single snigger in the house.
Next time I will actually talk about Hamlet the planet itself.
It’s recently been asserted, with some evidence, that the Solar System may be an exception in certain ways. We have moved from the assumption of mediocrity, also known as the Copernican Principle, that there’s nothing remarkable about our solar system to the realisation that it may in fact be quite peculiar. Specifically, one of the weird things about it is that it consists of planets moving in roughly circular orbits with small rocky ones near the centre and gas giants further out. Also, the most common type of all the planets type is between the sizes of Neptune and Earth, and we don’t even seem to have one of those, although it’s possible that it’s orbiting too far out to have been detected so far, perhaps having been thrown out early on. Another common feature of solar systems, though probably an artifact of how exoplanets are detected, is the prevalence of “Hot Jupiters”: planets around the range of Jupiter’s size which are however very close to their suns and far hotter than any of the planets orbiting ours, with atmospheres of vaporised metal and clouds of what would be minerals on Earth. It’s been hypothesised that Mercury is a leftover of such a planet, although if it is, it’s surprising it didn’t disrupt the Solar System so severely that it destroyed or flung out most of the other planets.
What I have in mind today, though, is a bit different. It’s about the relative sizes and masses of the planets. It was noted in the mid-twentieth century CE that the planets had a trend of increasing size up to Jupiter and then decreasing to Pluto, when Pluto was considered a planet, the exception being Mars. This led to the Tidal Hypothesis, now discarded, that they formed when another star approached the Sun and pulled out an enormous filament which resembled a cigar or spindle, in that it was thin at one end, much much thicker in the middle and thin again at the other end, just like Anne Elk’s theory of the Brontosaurus which was hers.
This theory was replaced by the Nebular Hypothesis, originally devised by Immanuel Kant in the eighteenth century, which came back into vogue. Incidentally, Anne Elk’s theory of the Brontosaurus does actually count as a genuine theory, not just an hypothesis. It could be refuted by the discovery of a “Brontosaurus” (that name is deprecated) with a short neck or a “Manx” Brontosaurus without a tail, although it would have to be demonstrated that the tail, for example, was absent rather than missing due to such factors as predation or geology. Incidentally, Brontosaurus is now once again considered to be a valid genus, after going through a long period of doubt, so there is hope for Pluto yet.
Another notable aspect of the Solar System is the spacing of the planets, which also appear to obey a law. Taking the numbers 0, 3, 6, 12 and so forth and adding four to each accurately predicts the relative distances of most of the planets from the Sun. However, this could be coincidence because some of this is kludged. Neptune doesn’t fit into the sequence, Mercury corresponds to 0+4 and not really in the series either, Pluto does fit in but is no longer officially a planet and the approximate position of the asteroid belt, and more specifically Ceres, is correctly predicted but again the asteroids are not major planets. Hence there are up to four exceptions out of nine, considering Pluto as a planet but not Ceres, which makes the “law” a bit shaky.
However, what I want to concentrate on today is the oddity that both Uranus and Neptune and Venus and Earth are “twins”. I’ve mentioned the Uranus/Neptune issue already, though in a different setting. They are both quite similar in size and mass, and they also look quite similar, Neptune being bluer than Uranus and Uranus being hazier and blander-looking than Neptune. Neptune is 18% more massive than Uranus, which is less than it sounds because mass is somewhat related to volume, but is also considerably denser at 1.77 times water compared to Uranus’s 1.25, and in terms of diameter Neptune is five percent smaller. Turning to Earth and Venus, we are 22% more massive and five percent larger in diameter. Taking these four planets out of the picture, the two most similar planets in this respect seem to be Mercury and Mars, whose surface gravity is almost identical, but Saturn and Jupiter are not that similar, Saturn being quite serene and calm-looking (although I’m sure it isn’t) and Jupiter quite manic and boily. Uranus and Neptune are more similar to each other than Earth and Venus in terms of conditions, with similar colours, atmospheres and to some extent temperatures, although Neptune’s day is much shorter. Probably coincidentally, both Uranus and Venus spin in the opposite direction to all other planets, are the further planet in and are slightly less massive, although all of these are likely to be coincidental. Uranus is unusual in orbiting on its “side”, the axis being almost parallel to the plane of the orbit, and is technically retrograde but only just.
Two questions occur to me here. One is whether these two sets of twins are just coincidence or more significant, and the other is how common twin planets are in the Universe. I don’t fully know how to answer either of these questions although I kind of played with the idea in the post linked above. One thing which is notable is that both sets of twins are one and two orbits away from Jupiter, which would work well with the Tidal Hypothesis although that’s now been rejected. It might, however, reflect either a tendency for the solar nebula to bulge at a mid-distance and taper off closer to and further away from the Sun, or a tendency, which may be the same thing, for Jupiter to pull matter toward itself. However, the spacing of the outer Solar System is much wider than the inner.
Earth is obviously the object of more scrutiny than the others, and a couple of things should be noted about us. One is that we used to be more massive and bigger than we are now, since our planet collided with Theia, a Mars-sized body (and I can’t help wondering if it actually was Mars but I expect this has been considered and rejected) and chipped off an eighty-first of the mass in the form of our natural satellite, which is anomalous in size. Just adding the volumes together gives the original Earth a diameter of around 12 841 kilometres, makes it slightly less dense and slightly reduces the surface gravity. It’s very salient to the question of life elsewhere to consider how Earth would’ve turned out had this event not taken place, but right now I only want to talk about the likelihood of twins in a star system. Earth also has a year 11.86 times shorter than Jupiter’s, suggesting that the matter this planet is made of was pulled away from a zone either side of a dozenth of Jupiter’s year by continual tugging when the planet made its closest approach. Doing the same calculations with Uranus and Neptune, the former has just over seven times the period of Jupiter, closer in fact than Earth’s to an integer fraction, and the latter is around twice Uranus’s. Venus is not close to either Earth’s sidereal period (year) but is close to a third of that of Mars. It would be interesting if it turned out that Venus was able to win the gravitational battle with Jupiter to cause Mars to form, but not to the extent that Jupiter was able to disrupt any planet which would otherwise have formed from the asteroids plus a very large amount of extra mass which would’ve been necessary for a planet to form in what became the asteroid belt. However, although it’s feasible to do the maths for all these planets, the point comes at which mere coincidence would appear to stand out, particularly when one considers that all sorts of resonance ratios need to be considered.
It’s very easy to speculate and not very scientific to do so. Nevertheless, the patterns here seem to be that both pairs of twin planets are next to each other, one of each has close to a multiple of Jupiter’s orbital year and the other hasn’t and both are some way between the apparently most massive region of the solar nebula and the thin edge. There could be another reason why the biggest planet is in that location. Perhaps it’s simply that collisions between particles are more likely either to propel them towards the halfway point (which it isn’t any more, incidentally) or less likely to leave the solar system entirely, so there’s a build-up but not due to a thicker ring of material as such. Another, very important, factor, is that lighter elements, or those with lower boiling points, are likely to be driven off the centre of the disc and be retained the further out they are, which goes some way towards explaining the distribution of small and large planets but fails to account for Uranus and Neptune, as by this token they should be the largest if that’s the only or a major factor.
I’m very much in the dark here. I don’t think this has often been remarked upon. Venus and Earth have often been compared and contrasted, as have Uranus and Neptune, but the fact that this happens twice in this star system alone seems remarkable. All the planets involved are of intermediate mass, although Earth is the largest and most massive inner planet. There is a somewhat similar case with the star system TRAPPIST-1, with eight detected planets all between the masses of Mars and slightly more than Earth, and all in roughly circular orbits and closer to the star than Venus is to the Sun. This is somewhat extreme and unusual, but due to the small size of the star it might make sense to think of it as rather like a planet and its moons, similar to Jupiter and Saturn, more than a solar system like this one. Considering the moons of the outer planets, although the largest of Jupiter’s have somewhat similar size in terms of order of magnitude rather than being quadruplets, Saturn and Neptune each have one larger moon and many smaller ones and Uranus has two sets of twins, Titania and Oberon, and Ariel and Umbriel, although they are next to each other in that order outward. Saturn’s mid-size moons are all quite distinctive but often similar in size to others, so they can’t really be thought of as twins in the sense that Uranus and Neptune can, although Venus and Earth are substantially unlike each other apart from size and internal composition as well. Therefore, perhaps there are two trends, again reflected in our own system, of similar and dissimilar twins, and stretching the point somewhat, might this mean that there are similar and dissimilar twin planets elsewhere? That this is characteristic?
In particular, might there be twin mid-size planets in inner solar systems? The type of planet which isn’t in evidence in our own Solar System which is intermediate in mass between Neptune and Earth, somewhat dissimilar to each other owing to their closeness to the star seems highly plausible. Probably the cause of the differences between Venus and Earth by contrast with the rather similar Uranus and Neptune is that, being closer to the Sun, the temperature and radiation gradient is greater and their environments are therefore more different, leading to them being less similar.
Suppose, then, the following hypothetical situation. A planetary system has a super-Jupiter situated where our asteroid belt is relative to its own sun, making it the fifth planet, 2.8 times Earth’s distance from the Sun. I’m assuming it has to be larger in order for mini-Neptunes to form in the inner Solar System. These would then both be between the orbits of Venus and Mercury, and therefore both rather hot, though not as hot as Mercury, at least at the cloud tops. They would therefore have lost much of their light gases and shrunk in size, but would still be around 50% larger than Earth and Venus in diameter. However, being watery, both would probably still have runaway greenhouse effects. I’m not going to try to come up with a scenario where life could emerge, because this is a very common skew in how planets tend to be discussed. This is more to do with trying to illustrate the diversity of planets in the Universe.
Another possibility is a system where a Jupiter-sized planet formed at the distance of Saturn from the Sun, and incidentally like the previous example I’m trying to keep the model simple here by presuming the star has the same characteristics as ours. This could place two roughly Earth-sized planets where our asteroid belt and Mars are. The outer twin here is of a type absent from our system once again, possibly with liquid ammonia oceans and an atmosphere with some hydrogen. Water ice would never melt on this planet. There might also be formaldehyde mixed with ammonia in the oceans, making this planet hostile to life but very suitable for preserving biological specimens! The closer planet would occupy the orbit of Mars and be a “snowball Earth”, with conditions over most of the surface like those of Antarctica. In this case, life is possible around volcanic vents at the bottom of frozen over lakes of water, but the atmosphere would be largely nitrogen with dry ice on the surface. This assumes, of course, that the planet is unaffected by any filter, such as phosphorus availability, which would rule life out.
A final scenario to consider is the possibility of twin planets formed through the influence of a Hot Jupiter, further out from the star. A Hot Jupiter a tenth of Earth’s distance from the Sun could end up causing two medium-sized planets to form. It would itself have an eleven day year with frequent transits visible from those planets, which could be situated at about the distance of Mercury and about halfway to Venus. If they were about Earth-sized, the outer one would probably just be Venus-like, but the inner one might well have practically no atmosphere and therefore be heavily cratered, but otherwise Earth-like in size. This is again a planet unlike anything in our system.
All of this is highly speculative of course, but the main point is to illustrate that there might be many “twin worlds” out there about which we know practically nothing, all very different from anything in our own solar system. But as a concession to the fixation on Earth-like planets, it’s also possible to envisage a pair of worlds whose mean distance from their Sun is the same as Earth’s. The inner twin could be like the classic, golden age sci-fi version of Venus, a steamy, hot jungle planet permanently swathed in water vapour clouds with heavy rainfall, and the outer could be a chilly version of Earth, with Arctic and Antarctica conditions but maybe conditions in the tropics comparable to Scandinavia. This could well be a star system with two habitable worlds, and perhaps two worlds with Earth-type life on them.
There is another way of getting twin worlds, which might be called “conjoined twin worlds”. Earth was split into two bodies by the Mars-sized Theia. A larger planet-sized miscreant might have split our planet into two roughly equal-sized planets orbiting each other. The difficult thing to manage here would be the distance between the worlds, as if they were at the same distance as our own double planet system, their rotation period would last several weeks and temperatures would fluctuate between conditions which would boil the oceans and conditions which would freeze them solid, so this would be a nasty pair. However, if they were quite close, but not close enough to tear each other apart, they would form two smaller, more arid and mountainous worlds with less water but deeper oceans. These would then be desert worlds, perhaps with deep lakes rather than oceans, and mountains reaching high above the cloud tops, which would in any case be lower than on Earth, perhaps with whole plateaux above them where it neither rains or snows. However, the mean temperature at a given latitude could still be comparable to ours. But there could equally well be double Veneres or Martes, and in the latter case it would likely be a pair of cold Mercuries.
To conclude then, I think if we get to adequately explore the Galaxy, evidence from this star system strongly suggests that there would be plenty of twin planet situations, and as far as I know this has never been explored theoretically by astronomers. Nor, so far as I know, has the fact of there being a pair of twins here been investigated. I’ve used a fairly naïve model to imagine the planets here, but even if I’m wrong, and I probably am, I still think that there are likely to be many twins in the Universe, and I look forward to some being discovered.
In 2006 CE, the International Astronomical Union declared a new definition of “planet” which excluded Pluto because it didn’t satisfy the new criteria. These were:
It had to orbit the Sun (or presumably another star or it’s very silly).
It had to be almost round (so no doughnut-shaped planets?).
It had to have cleared the neighbourhood around its orbit.
They did this because a number of large new objects had recently been discovered which were round and two, I think, were more massive than Pluto, but they didn’t want to call them planets because it would’ve led to a very large number of bodies ending up being called that. They also introduced a new category of “dwarf planet”, which included Ceres, previously regarded as an asteroid, and also Pluto and others. It does make sense to do this, although I don’t understand why they didn’t just carry on with the term “minor planet”, referring mainly to asteroids, or perhaps “planetoid”, which they’d also used a lot.
The least clear of these three criteria is “clearing the neighbourhood”. This means that a body has no other bodies of comparable size other than its moons or other bodies under its gravitational influence such as Trojan asteroids. These are asteroids which orbit 60° ahead of or behind a planet in the same orbit which are pulled there by the gravity of the Sun and the planet concerned, examples being Achilles and Hector with Jupiter. Arguably this criterion either makes Cynthia a planet or Earth not a planet, and whereas I’m fine with the former I don’t think the latter is sensible.
The word “planet” has been applied differently during different times in the history of astronomy. When the large Galilean moons of Jupiter were discovered in the early seventeenth century, they were referred to as planets, and this also happened when Ceres was discovered in 1801. A similar process to the one leading to Pluto’s demotion then ensued, with lots more “planets” being discovered until it was decided to call them minor planets or asteroids.
It’s actually quite nice to think of Cynthia as a planet because it increases the number of known planets in our Solar System to nine again, and also means the Apollo astronauts landed on another planet rather than just a moon, and it also bolsters the idea that it should have its own name. It’s the largest body within the asteroid belt which isn’t considered a planet. Leaving that aside though, one issue with Pluto not being a planet is that most people have grown up with the idea that it is one, and it’s hard to let go of apparent certainties arrived at in childhood. Its demotion is akin to the youth of today liking different music or something. To quote Abe Simpson, “I used to be with ‘it’, but then they changed what ‘it’ was. Now what I’m with isn’t ‘it’ anymore and what’s ‘it’ seems weird and scary. It’ll happen to you!”. And it did. It happens to all of us.
I exploited this idea in my Caroline Era alternate history with the discovery of Persephone and subsequent visit by Voyager III. This body is in fact either Eris or Sedna, I can’t remember which. There is also an eleventh planet according to the Caroline Era astronomers, which is whichever one this isn’t, and this could’ve happened. It isn’t an alteration to the solar system, just to what we call things, and the name Persephone has been hanging around waiting to be attached to a new outer planet for a very long time now.
When Neptune was discovered, its mass and position explained some of the vagaries of the Uranian orbit but not all. Neptune also takes more than a gross years to orbit the Sun, so it was too slow-moving to plot its orbit accurately for quite some time after its discovery. Therefore, it was conjectured that a further planet must exist beyond the orbit of Neptune. Two planets were proposed, one by the well-known Percival Lowell who elaborated the Martian canals. He proposed a planet seven and a half times Earth’s mass with a mean distance of around 6 500 million kilometres from the Sun and a period of 299 years. It would have had a diameter of around 25 600 kilometres. Those figures, which turned out to be very wrong for Pluto, are worth remembering because they suggest something else, but I’ll be coming back to this. The other proposal was from Edward Charles Pickering. He suggested a planet with a mean distance of 8 200 million kilometres from the Sun and a period of 409 years. Obviously it couldn’t be both. Incidentally, this is where “Planet X” comes from. It was Lowell’s name for this planet while it was still undiscovered. Then, after a lot of searching using photographic plates to detect the movement of the body against the background of the stars, Clyde Tombaugh detected something moving in approximately the right position. After a competition, the eleven year old Venetia Burney decided it should be named Pluto, because it was far out, dark and gloomy and therefore appropriately named after the god of the underworld, which also happened to begin with Percival Lowell’s initials.
Both astronomers had predicted a highly elliptical orbit in comparison to the other planets, and in fact its orbit is indeed considerably more elliptical than any of them apart from Mercury, and was still quite a bit more eccentric even than that. For a long time, Pluto’s satellite Charon remained undiscovered due to being very close to Pluto in both distance and size, and consequently there was no easy way to calculate its mass, so it seemed that in order to yank Uranus around sufficiently from that distance it had to be practically a solid ball of iron, probably the densest element found in large enough quantities to make up an entire planet. If Charon had been found earlier, its orbital period would’ve indicated that Pluto was in fact not very dense at all and mainly made of ices, so when it was discovered in 1978, or more likely somewhat later when its month became known, it was realised that Pluto was not nearly massive enough to account for it. Its density is only 1.88 grammes per cm3 rather than more than four times greater as it had had to be assumed. So it looks like Pluto was actually just discovered by chance and has nothing to do with perturbing Uranus. Astronomers just happened to be looking really hard at the patch of sky it was by chance crossing at the time. It was in fact fainter than expected too, because they thought it would be larger, and the size of Pluto was also overestimated for a while for the same reason as its mass. In fact, to fulfil requirements it would actually have had to be more than twice as dense as the densest atomic materials in existence. Note that that doesn’t mean “known”. The densest elements are already known because the strength of the nuclear strong force compared to the other forces in atomic nuclei allows the heaviest stable elements to be determined, and they’ve already been discovered in the form of osmium and iridium.
Pickering believed that his planet and Lowell’s were not the same, and that both existed. To return to his “Planet P” as he called it, it’s of a type which is nowadays referred to as a “Super-Earth” or “Mini-Neptune”, and these are notable by their apparent absence from our Solar System. Of all the planets discovered in the Galaxy by the current rather flawed method, the most common of all are of this type: considerably larger than Earth and considerably smaller than Neptune and Uranus. It is in fact an unresolved problem in astronomy that the apparently most common type of planet also seems to be completely absent from our own system. Some have suggested that at some point a Super-Earth did indeed orbit with us but was slung out of the system entirely, or way too far out to be easily detected, æons ago, which is why we seem so atypical.
Before I go on to the next bit, I want to talk about Uranus and Neptune, both of which were “precovered”, i.e. noted before it was realised they were planets. William Herschel published his ‘Account Of A Comet’ in 1781, where he thought he’d found a comet but it turned out to be Uranus. This planet is actually just about visible to the naked eye and could easily be mistaken for a star. Neptune is too faint for this to happen, although I wonder if nocturnal animals can see it as well as Uranus, so the idea of it being discovered when it was may be preceded by perhaps 200 million years or more, although that would only be an early mammal happening to notice a light in the sky rather than a genuine discovery. It is, though, possible that Neptune was recorded as a star by various astronomers before it was actually found to be a planet.
And this brings us up to date, because as you probably know, a ninth (tenth‽) planet may have been discovered through old telescope photographs. The IRAS project, from a satellite launched in 1983, was an infrared sky survey operating for nine months. As seen highlighted in the image at the top of this post, it may have found a new solar planet. The object in question is in roughly the right place for Planet 9 but may not be a planet at all because it’s close to the galactic plane, where there’s a lot of dust and stars, making observations rather difficult. If it is a planet, it’s about 225 AU from the Sun (33 750 million kilometres or one light day and seven light hours from it) and has a mass at least five times Earth’s. If that difference is average it would take more than three millennia to orbit the Sun and the last time it was in the position it was in 1983 would’ve been in the late Bronze Age. It may well not be a planet at all.
The reason Planet 9 might exist is that the Pluto-like bodies orbiting between 150 and 300 AU out – those are average distances by the way and the orbits are far from circular – seem to be clustered on one side of the Sun but are too far out to have their movement disturbed significantly by the gas giants we know about, so the idea is that there is a planet even further out which influences their motion. Although I’m in the Dunning-Kruger zone with this, I have my doubts because it seems to me that the bodies we know about are all currently near their closest approach to the Sun because otherwise they’d be too dim and slow to be detectable, and it could be an artifact of a small sample size. I may well be wrong about this. If it exists, the planet in question would be about five times Earth’s mass, as stated above, but also 400 to 800 times further out than us as opposed to 225. However, Pluto was discovered because of looking in the right place accidentally, so although the hypothesised planet is too close, it doesn’t mean it isn’t there. Presumably it could mean there’s yet another one further out. Some people are uncomfortable calling it “Planet 9” because they see it as insulting to Clive Tombaugh. I feel a strong urge to call it Persephone. It isn’t the hypothetical Tyche, because that would be larger than Jupiter and has been ruled out by observation at any distance closer than 10 000 AU. Tyche would actually be fairly warm incidentally, because it would be large enough to heat itself – it would be only slightly cooler than Saturn.
A super-Earth at that distance, though, would be very cold. I’m not sure how cold exactly, but it would be between -270°C and -195°C. Planets of this type are either water worlds or “gas dwarfs”. At that distance it seems unlikely it would have oceans because they’d be frozen solid, but one depiction of a gas dwarf is that it would be like this:
It could also have moons, which I find interesting because they could be warmed by tidal forces and if not, might have neon-rich atmospheres if they’re large enough.
The subject of Super-Earths and/or Mini-Neptunes is worth holding over for a post in itself, so I won’t go into more detail here, and I really think this is going to turn out to be nothing, but it’d be nice to discover another planet in our Solar System and perhaps resolve the problem of why we don’t seem to have one of this type. Alternatively, maybe a planet at that distance is far enough out to have been a rogue planet wandering between the stars or to have belonged to another solar system entirely which passed too close to the Sun and had one of its planets captured, which is exciting as well because it means we’d be able to study a planet from another star at relatively close range. It’s still over a thousand times closer than the nearest star though.
So to conclude, because good science always goes for the most boring option, I don’t think this is Persephone, but it’d be nice if it was.
A Box Of Chocolates 