I often do bait and switch on here and I should honour the title to some extent, so here it is. There’s much to admire about David Bowie and the world lost a genius a few years ago. I’ve blogged about him before and whereas I can’t be bothered to fish those bits out I do remember tracing his reference to superhumans in ‘Oh You Pretty Things’ back via Arthur C Clarke’s ‘Childhood’s End’ to Olaf Stapledon’s writing, particularly ‘Odd John’. But that isn’t what I’m thinking of right now. I’ll never forget the first time I heard ‘Space Oddity’. It was an oddity to hear that accent on the radio. I don’t know why exactly, because there were lots of southern English rock stars at the time, but somehow it seemed really, I don’t know, ground breaking. Of course he was groundbreaking in other ways. My ex is a big Bowie fan, and has found him a gateway into sci-fi, a genre she previously despised, but as I said to her, and for some reason I think this applies to him in particular, you can’t take things too far from his lyrics without ruining them. For instance, in the album ‘Ziggy Stardust’ and his Mott The Hoople single ‘All The Young Dudes’, we seem to be expected to believe that there will be a mains supply for electric guitars, organs and amplifiers during the apocalypse. In fact, maybe there will be and that’s a mark of his visionary nature, but it bothers me. They should’ve been acoustic.
What I have in mind today though is ‘Life On Mars’. This has now famously been used as the basis for the excellent time travel police procedural series, which to me felt like Sam Tyler travelling back to a time when things were “normal”. Unsettlingly, that series itself is now almost twenty years old and the same gap separates us from Windows 3.1 as Sam Tyler from Gene Hunt. Well, sort of – no spoilers! My take on the track itself, though, is that it’s about someone despairing of how life is here on Earth and hoping there’s life on Mars instead because at least then there’d be something better out there. I’ve said before that my greatest fear is that there is no life elsewhere in the Universe, mysterious encounters in Sussex chalkpits notwithstanding. This is also why I’m so peed off with the scarcity of phosphorus. Anyway, this is in fact a major reason why I’m so focussed on the possibility of alien life. I may have just written a nine thousand word long rambling blog post about silicon-based life, but the subtext is the same as Bowie’s song’s. As Monty Python put it, “pray to God there’s intelligent life somewhere up in space, ‘cos there’s bugger all down here on Earth”. I don’t entirely agree with that by the way. I think many of us choose not to think complexly, which is one reason we’re in this mess.
Okay, have I done enough of that now? Enough relatable stuff? Seriously though, I’ll try not to go off on one.
Because as you must know by now, it really looks like there might at some point have been life on Mars, according to recent discoveries there. I have to admit that at this point in the proceedings I have little idea what they’ve found, but I seem to remember it’s an iron compound which is found as a product of terrestrial life, possibly a sulphur one, which needs to have quite a lot of energy input to form but is then stable and has no known non-biochemical routes to its formation, that is, including the biochemical route involving the evolution of a technological species which can do sums like many of us, which I’m sure nobody sensible is suggesting. This is the latest stage in a long history of claims about Martians, and at some point it was considered so certain that there was intelligent life there that a competition for ways to communicate with aliens specifically excluded Mars because it was thought too easy. There have been claims of canals, lichens, and later on a scaled-down set of claims regarding something like bacteria. In particular there was the Labeled Release (American spelling) Experiment on the Viking lander which appeared to show positive results, i.e. the results which NASA had pre-decided would be best explained by life, but the problem was that the other two experiments were negative. It’s frustrated me until recently that they did this but right now it seems more like the way the scientific method works: come up with an idea, test it and then do everything you can possibly think of to prove a positive result wrong. On the other hand, looking at it non-scientifically at the time, it felt like they were in denial about the existence of life, possibly because it’s an audacious and potentially career-ending claim if it ends up being refuted, but also because it’s such an Earth-shattering claim. But this puzzles me a bit because in fact for a long time, since at least 1877 up until 1965, it was basically considered a dead cert that there was life there, and often also on Venus at the same time, and it didn’t seem to make much difference to the human race that we thought it was out there. Maybe this is to do with most people not being very focussed on space, but at least in the ’50s and ’60s this was definitely not so and in fact this was probably one source of inspiration for Bowie’s track. Getting back to Viking, it’s now thought that the results of the experiment were caused by perchlorate in the soil, a bleach-like substance which it’s also been claimed originated from the sterilisation process in the reaction chamber before the lander left Earth, although I think it’s now established that perchlorate is high in Martian soil. In fact I seem to remember (look at me failing to check my sources – sorry) that it makes Andy Weir’s ‘The Martian’ unfeasible, though maybe ingenuity would’ve got him out of his predicament some other way. Weir has since said that Watney could’ve washed it thoroughly first, so maybe, although wouldn’t he then have ended up with most of his water full of bleach? Maybe not. I’m not a chemist. There’s also been a view that the dendritic appearance of some terrain close to the poles is due to the action of microbes, something I went into in depth when I put the Martian calendar for 214 TE (telescopic era) together if anyone remembers that – it involved me throwing an inkjet printer into the larder with considerable force at one point.
What’s happened is that the Perseverence Rover in Jezero Crater has found what they call “leopard spots” on rock samples. Organic carbon-containing mudstones have been found to contain nodules and reaction fronts rich in ferrous iron phosphate and sulphide minerals. Vivianite is one possible candidate, which probably coincidentally is found in bivalve shells, and another is greigite, which is a ferrimagnetic mineral regarded as a biosignature, in other words a sign of life. Other processes which could have produced these minerals involve heating which doesn’t seem to have happened to the rocks in question as they would show other signs, for instance in their crystal structure. It seems that redox reactions have occurred there, that is, reactions involving the transfer of electrons between substances, one example of which is burning and another internal respiration. These rocks are around three thousand million years old, and at that time the same chemical reactions were occurring on Earth, mediated by microorganisms. So there are these two neighbouring planets on both of which chemical reactions usually associated with life are taking place. On Earth, it’s known that this is due to life, but what about Mars? The paper in question has eliminated other possibilities as likely explanations. Further investigation by NASA is of course not likely to occur due to funding cuts, but China might end up doing a sample return mission, that is, bringing samples back to Earth, in the next decade.
For me there are a couple of takeaways from this. One is that space exploration moves agonisingly slowly. This is probably an artifact of being born in the 1960s CE., but I was under the impression that there would be a human mission to the Red Planet from 1979 to 1981. This then got repeatedly postponed. The other is that science tends to do the same thing, although it’s also punctuated by revolutionary bursts of activity, according to the philosopher Thomas Kuhn anyway. It’s very cautious and tries hard to be boring. We seem to be edging very gradually into a position of accepting that there has been life elsewhere in the Universe, and that it was also found elsewhere in this solar system in a similar condition to its state on Earth at the time. Whether it exists on Mars now is another question, although of course “life finds a way”. Whereas that’s a bit of pop-culture tat, there is an element of truth in it and to be fair it’s quite a good line. You only have to look at a seedling growing between two paving stones to see that, but living on a practically airless, arid rock bathed in ultraviolet and dropping daily below the temperature of Antarctica is a considerably taller order than that. Maybe.
There are several possible worlds in this solar system other than Earth which may be hospitable to life as we know it. These include Venus, Mars, Ceres, Ganymede, Callisto, Europa, possibly Jupiter, Enceladus, Titan and maybe even Triton, Pluto and Charon. Several of these are quite a bit friendlier to it than Mars, although the question of it arising in those places in the first place also arises. Maybe it didn’t arise on those worlds though, and simply seeded them having arisen in space. If that’s so, maybe it’s the cloud that formed this solar system which gave rise to life, which then arrived on various planets, moons, asteroids, comets, wherever, and either died or, metaphorically, took root there. If that’s so, with reference to the previous post on here, it would probably show up as having the same chirality of molecules as we, i.e. left-handed proteins and right-handed carbs. It’s been suggested that life here must have pre-dated the Earth for two reasons: it seemed to arrive almost before it was possible for it to form, and looking at mutation rates in DNA takes it back to a point before the formation of this planet. To clarify, there’s a set mutation rate in DNA and RNA which enables scientists to date roughly when diverse organisms had a common ancestor, and incidentally this is usually before the first definite members of two groups turn up separately as fossils, which could mean a couple of things. The complexity of many genomes has increased over time as well, and this too can be measured from the genes which organisms still share. If you extrapolate these rates back to the point where the minimum information for an organism to function is present in the genome, you get a period of about nine or ten thousand million years ago, or roughly twice the age of the Earth. This isn’t generally regarded as solid evidence though. What it does suggest, interestingly, is that not only does life here descend from organisms present in the solar nebula, but actually it’s from a source which existed before this solar system had even begun to form.
I’m not going to base anything firmly on that possibility, but others have been suggested, one of which is that life arrived here from Mars aeons ago, which is supported by the likelihood that Mars was probably actually friendlier to life back then than Earth was. These redox reactions may be from the exact same taxon of organisms on both planets. And this is where it gets difficult.
David Bowie asked “is there life on Mars?”, but was this the right question? Many people have said that if life can be found there, or in or on any other world in this solar system, it guarantees that there’s life elsewhere in the Universe. Well, it really, really does not. Suppose we do find incontrovertible evidence that there is, just now, life on Mars, and also on several other worlds in this solar system, and moreover that it’s remarkably similar in some ways to life on Earth, for instance possibly sharing some genes with us, and has the same chiralities in proteins and carbs as us. That means that all of that life has a common ancestor. That common ancestor might have arisen in this solar system, or at least locally before this solar system formed. In terms of chirality, maybe there’s something about the processes of the Universe which lead right- and left-handed molecules of the respective types to form and persist while their mirror images don’t, or maybe there’s something about mirror life which means it won’t function, in which case all life of the kind we know in the Universe would have those chiralities for some very fundamental reason, but we’re still drawing conclusions from a very small sample. Maybe there’s either just something about this solar system which makes it more likely that life would emerge here, such as the relative abundance of phosphorus, or maybe it just did emerge here against all odds because we live in a very large Universe, many of whose planets are covered in a reddish-brown tarry goo instead of life.
For all we know, planets and moons here could be rich in life forms, and that would be a cheering thought, but that doesn’t of itself guarantee that the rest of the Cosmos is not utterly barren. For all we know, there could be endless lifeless worlds filling the Universe, which nothing whatsoever wrong with them but simply because the chances of it arising are vanishingly small. I’m sometimes haunted by the thought of some very, very Earth-like planet orbiting, I dunno, Delta Pavonis or whatever, with a perfectly comfortable surface temperature, oceans, continents, rain, thunderstorms, rainbows, mud, puddles children would love to splash in, sunsets over idyllic beaches lovers could walk along, or other phenomena alien beings could appreciate in their own way if they existed, but which will never, ever even see a single bacterium before their stars overheat and destroy them. Trillions of them, all without life. And this solar system being full of life would be of no significance, no consequence to that situation, because life just arose this one time. And this is why I say that if it could be proven that life existed nowhere in the Universe, I would stop worshipping God. It’s like a deal-breaker in a relationship for me. I would be terminally angry with such a Creator for sustaining in existence such a vast and uninhabited Cosmos. It would be really bad.
This, then, is why I say David Bowie is asking the wrong question. It’s the right one if understood in terms broader than just Mars, that is, if Mars is just a stand-in for another planet or other location where life could persist. Mars is just our next door neighbour, and we already know our bushes might end up growing over the fence or our aphids might end up infesting next door’s roses. Big deal. The Universe is so big that the size of this solar system is nothing to it.
My eyesight is terrible. When I go to the opticians for a new prescription as opposed to handing over the new one, they use a special chart with a single letter filling all of it and ask me if I can see it at all, and the answer is always no. Because of this, as a child I expected to go blind and trained myself to find my way around without looking, which annoys Sarada as it seems to mean I notice details more than I do large objects, although that’s probably partly an aspect of my neurodivergence.
Therefore, in general when I look up at the night sky without binoculars or a telescope, I see very little because the starlight is too blurry if I don’t wear glasses and if I do the lenses cut out most of the light. Most of the time, it’s hardly mattered because, for example, in Loughborough the sky was overcast at night or ruined by street lamps. However, here in southwest Scotland, the situation is different, rather like that in and around Herstmonceux, where I trained as a herbalist and where the Greenwich Observatory was moved when the skies got too bright. This region is one of the dark sky sanctuaries, although apparently it gets darker even than this a little to the west:
Compare this to South to Mid-Wales, the South of England and the English Midlands:
Much of Devon and mid-Wales are fine there, but I’ve never lived anywhere near them, and the area around Herstmonceux is now pretty much the same as the rest of the South nowadays.
Surprisingly, on looking at the sky here, as I did the night before last, through binoculars and with my eyes plus spectacles, I was able to perceive another, well, spectacle in the form of a clear sky and a vista out into the local arm of the Galaxy, as well as of our closer neighbours Mars and Jupiter. The lunar absence helped but the magnification of the binoculars decidedly didn’t, as it was impossible for me to hold them steadily enough to see either planet clearly. For some reason the binoculars I use are 16 x, which I understand are usually mounted on a tripod for this reason but they don’t have anywhere to screw them in. I’m guessing you can get a frame of some kind to address this issue but I don’t think I have one. Frustratingly, I finally found the telescope yesterday, too late to aim it at the sky on that particular occasion but tomorrow is another night.
It was helpful that Mars was so clearly visible. I understand it’s currently near opposition, i.e. about as near as it gets, because it’s quite distinctive and enabled me to find Castor and Pollux, as it’s currently in Gemini, which in turn helped me find something I’ve never managed to see before: Praesepe, also known as the Beehive Cluster. Before I dilate on this, I want to point out that turning one’s attention to the stars is a fantastic escape from the troubles of this microscopic blue dot, and perhaps also a unifying factor, but there is unfortunately nowadays a fly in the ointment because of Elon Musk’s satellites interfering with a clear view of everything. However, I don’t want to dwell on that.
I’m sure you’re familiar with the bundle of eggs a spider lays – a ball made up of the mother’s embryonic young yet to hatch. When they do emerge, they scatter themselves having eaten the mother’s body, at least according to ‘Blade Runner’ if that’s not a false memory. This brings to mind how stars form in globular clusters like this:
Sid Leach/Adam Block/Mount Lemmon SkyCenter
After a while, they fly apart and the result is an open cluster like the aforementioned Beehive. Other nearby examples are the Pleiades and Hyades, quite nearby in our sky. Cancer, the constellation where the Beehive is, is generally quite dim and I had the impression that the cluster was too but apparently its total brightness is something like 3.7. I should explain what this means. The faintest stars visible to the naked eye of someone with good eyesight are of magnitude six, and the brightest, one hundred times brighter, are around magnitude zero, an example being Vega. This makes it a logarithmic scale with each step around two and a half times that of the one above. It also illustrates that we perceive things such as brightness on a logarithmic rather than linear scale, and a similar scale for sound volume, decibels (which are not actually a unit of loudness but it’s too involved to explain here), doubles every three, so 86 decibels is twice as loud as 83. I’m just going to say one more thing about decibels which indicates their oddness: how far from the sound source are you when you judge it? A seventy decibel sound ten metres away becomes a seventy-six decibel sound five metres away because it’s four times as loud. But does it?
Praesepe, the Beehive, is a fuzzy patch in Cancer around six hundred light years away larger than the Sun looks in our sky, with a magnitude of 3.7. That means that all the stars together are that bright, and it’s the area which is that bright rather than the mean magnitude of all the stars in the cluster. There are supposed to be about two hundred stars in it altogether, although being an open cluster its edges are vague, although it’s about twenty light years in diameter. “Praesepe” means “manger” or “crib” (I’m from Kent so I say “manger” for both, which I suspect is dialect and I’ve never used it outside Kent, but I don’t honestly know), and it is in fact a nursery for stars, so it’s peculiarly appropriate. You only get one chance to use that though, so although the other open clusters are also nurseries they can’t be called that too. The Pleiades or Seven Sisters, probably the best known open cluster, consists of stars which are mainly roughly the same size and temperature as each other, being blue giants, but the Beehive is not like that. The Seven Sisters are actually younger than the extinction of the non-avian dinosaurs, but the Beehive is about six hundred million years old, so it’s considerably older than the first trilobites. It varies a lot more, containing white dwarfs, red giants and also yellow dwarfs, which are Sun-like stars. Moreover, several of these stars are known to have planets and one of them has at least two if I remember correctly (I always write this stuff off the cuff). However, as is very common, they’re all “hot Jupiters”, that is, they are red hot, partly vapourised planets which would’ve been rocky at a greater distance. Using the current popular method, hot Jupiters are easier to detect than other exoplanets because they’re large and closer to their suns, as it involves measuring fluctuations in brightness, which is likelier to be detected if the planet is relatively large compared to its primary and orbits it quickly. The planet also needs to be orbiting edge-on to our view. There are other ways of detecting planets but they haven’t been used for decades, and when they were it turned out they produced spurious results, such as simply recording when the lenses in telescopes were cleaned and put back at a different angle! Nowadays, it seems feasible that they would work, so I don’t know why they’re not using them.
There are roughly a thousand stars in an approximate sphere with a radius of ten light years, and those are just the ones detected from Earth. There are probably more because many of the known closest stars to our solar system are red dwarfs, the lightest and smallest stars, and the smaller a star type is, the more common it tends to be. A sphere with a radius of ten light years has a volume of around 4200 cubic light years, and with two hundred stars in the cluster that means a cube with a volume of 4.2 cubic light years on a side would contain on average one star and the mean distance between stars in the cluster would be only 1.6 light years. However, if they’re anywhere near randomly distributed, that distance is likely to vary quite a lot although the centre of the cluster might be denser, as can be seen from the photograph if those alignments are not optical illusions. There are many optical double stars in general which just happen to be along the same line of sight. This means that even given the known stars, which include red giants, the sky of a planet in the cluster would be a lot fuller and brighter than Earth’s, always assuming its atmosphere isn’t too dense or cloudy to see through and that it isn’t very close to its own sun. If we were that distance from α Centauri, it would be about as bright as Venus and capable of casting shadows, and if a red giant the size of Arcturus were involved it would be getting on for lunar level brightness and light up the whole sky.
Back in the 1960s or possibly the ’70s, a nuclear-powered starship called Daedalus was designed which couldn’t be built because it would violate treaties on nuclear weapons. However, if it had been, it could’ve reached the nearest star within fifty years. In a cluster such as this, it might take only twenty years to get there, which is a much more manageable interval. There are Sun-like stars in the Beehive and there’s no reason to suppose they don’t have Earth-like planets circling them, perhaps many such planets throughout the cluster. And there’s more.
One thing which really stimulates evolution here on Earth is frequent mass extinctions. For instance, something massive hit this planet sixty-six million years ago which led to the ascendance of the mammals. Various other causes led to other mass extinctions, some possibly due to other impacts. Had none of that happened, evolution might not have led to us appearing because life would’ve been too easy on this planet. Hardship and adverse circumstances lead to creativity here too. Furthermore, Earth is unusual in having a large moon, due again to a major impact, this time from an object the size of Mars, which led to the development of a strong magnetic field protecting us from ionising radiation. All of those events are more likely in the cluster due to its crowded nature, with stars interfering with each others’ comets and asteroids, but as said before, it’s only six hundred million years old and it seems unlikely that there could’ve been enough stimuli for even the simplest multicellular life forms to have evolved in that time. However, if that did happen in such a cluster, interstellar travel would be far easier to achieve than we find it, as would observation of other star systems. For instance, planets orbiting a Sun-like star would be on average sixteen times brighter when observed from adjacent star systems than they would be from α Centauri.
As I’ve said before, I try not to focus too much on life, intelligent life, life as we know it or humanoid life on this blog because that’s a bias which I think makes the Universe less interesting, and the emphasis on life is a bit anthropocentric and perhaps also rather science fictional.
Half the mass of the cluster is contained within 12.7 light years of the centre and its gravity is capable of pulling stars towards it from thirty-nine light years away. There are also stars moving through it which have no real association with it. It shares motion with the Hyades, the closest star cluster of any kind to us, and its composition is similar, so they were probably once part of the same structure. They are only 150 light years away from us.
First of all, an apology. I’m generally committed to not referring to our natural satellite as “the Moon” because perspective is important, so I often call it Cynthia. I regret choosing this name, although it’s a valid label since it is one of the Greek lunar goddesses. Some others are Selene, which I like, Diana and Artemis. There’s an association with hunting because a bright nocturnal celestial luminary renders prey more visible. All of these names have a Western bias, so maybe that could be addressed for once as it would be good if one of the best-known and oft-mentioned celestial bodies had a non-European name. Because it also seems weird and distracting to keep calling it (her?) Cynthia, and indeed “her”, much of the time I refer to our companion in circumlocutory terms, so for example I talk about astronauts reaching “the lunar surface” or do what I just did. This is actually already why it’s been called “Luna” rather than “Mensis”, the older Latin name, since “menses” refers to menstruation and the Romans seem to have felt like they were referring to a “period” in the sky, which could’ve been quite positive but they were the Romans so it wasn’t seen that way.
Now for lunar landing denial, and there’s the circumlocution again. Humans did land on the lunar surface. Twelve of them in fact, between 1969 CE and 1972. Many people only remember Neil Armstrong and Edwin “Buzz” Aldrin, so I’m going to list all of them here: Neil Armstrong, Buzz Aldrin, Charles “Pete” Conrad, Alan Bean, Alan Shepard, Edgar Mitchell, David Scott, James Irwin, John Young, Charles Duke, Eugene Cernan and Harrison Schmitt. There were also six command module pilots and three people who attempted to land but failed due to an explosion. Although I’m tempted to mention their names, along with the three Apollo astronauts killed on the launchpad, I think I’ve made my point: that twelve people have walked on the lunar surface. The reason this needs stating is twofold: most people have no recollection of the other ten and apparently lunar landing deniers are under the impression that there’s only one lunar landing to deny.
How can we be confident that they happened? Well, for example, there are laser reflectors on the surface placed there by Apollo astronauts used by astronomers all over the world, although also one on the Lunokhod automatic lunar rover put there by the Russians, footage of dust kicked up by the Apollo lunar rovers describes a trajectory only possible in a near-vacuum under about one sixth of Earth gravity, returnees develop cataracts significantly earlier than people who have never been there. Add to that that if it really was a conspiracy, all the people involved who knew about it would’ve had to have taken the secret to their graves or haven’t spoken up about it yet. I really can’t be bothered to go into too much detail about this, and other people have done it better than I could, but I’ll mention a couple of things. Stanley Kubrick’s ‘2001’ came out around the same time as the Apollo missions, so he is often named as a co-conspirator, but his lunar landscapes look like others did before they were refuted by images from low orbiters or the astronauts themselves: they’re craggy and covered in cracks because the surface was thought to be more or less uneroded, but actual pictures show soft, undulating hills and fairly thick dusty soil, which however, wasn’t as deep as some astronomers expected and didn’t engulf the Lunar Module or the astronauts. The absolute minimum that happened was that the astronauts orbited and dropped probes, and that there was a sample return mission, and if they did all that they may as well have genuinely gone there. So believe me: humans have walked on the lunar surface.
HOWEVER
There is another issue.
Suppose it’s 1968. Apollo has yet to take anyone to another heavenly body. Moreover, it probably never will. This is because if it did, and that was the start of humanity spreading out into space and settling on other planets across the Galaxy, and at the time many people thought it was, that would probably mean that the total population of the human race would dwarf the number of humans who have lived up until now, since at a very conservative estimate there could be a million Earth-like planets suitable for us to live on in the Galaxy. Each of those would only have to have a total population throughout their human history of less than a hundred thousand for the chances of being born before or after Neil Armstrong to be fifty-fifty, and that’s a tiny number of people. Therefore the chances of him setting foot on the Sea of Tranquility are practically zero unless it doesn’t lead to any further missions to settle, there or elsewhere, or for that matter build any space habitats. Therefore, from the perspective of the late 1960s it makes perfect sense to assert that the Apollo missions will either fail or be fake. They’re a hoax.
Only they weren’t, were they? As I’ve just said, the lunar landings happened. Returning to the present though, 2024 right now, the same argument applies, although it is in fact rather stronger because now, more humans have been born than in 1968. We live in a young world. The median age of the world population is now thirty, meaning that most people alive today have been born since 1994. We also lived in a young world back then, with the baby boom for example, though that was just in the West. More people have lived now, and all of them have still lived on this planet. The chances of this happening have fallen for everyone who was born since 1972.
This is of course similar to the Doomsday Argument, which I’ve mentioned on this blog before. The Doomsday Argument is an attempt to estimate whenabouts we are in human history by considering one’s birth as a random event in time. Given a thirty-year doubling time in human population growth and a birth in the late 1960s, such as mine, and assuming my birth was about halfway through the total number of human births ever, this would mean that the last human birth would take place around 2130. Right now, this seems to be an overestimate and for environmental reasons to do with climate change the human race can be expected to go extinct in about 2060. That said, human population growth is also slowing, and it’s a highly egocentric argument because if someone else, born say in 2006, were to make the same calculation, even given the same doubling rate of population the last human birth would take place quite a bit later.
We now have the Artemis program, aiming to return humans to the lunar surface in the near future, and to facilitate human missions to Mars. If this happens as described, it sounds like it would be the start of this species spreading into space and we are once again probably confronted with trillions of future humans whose existence entails that living before that happens is very improbable. This is the second time this has happened, in almost exactly the same way. The first time, it actually did happen. This time, just as I would’ve said in 1968, it won’t. Whatever has happened in the past has a 100% probability of having happened because it did happen. This is true in one sense. In another, it isn’t. For instance, if you chose a random nation state in 2000, it would probably be a republic, but if you chose one in 1700 it would probably be a kingdom, and the past can’t be perfectly known. It can, though, probably be known more accurately than many future trends and events. Anyway, this means that because humans did reach the lunar surface, they have a 100% chance of having done so. Paradoxically though, if the same prediction had been made in 1968, it would also probably be true. This does raise issues about the nature of probability.
There’s this thing called “immanentising the Eschaton”, which is forbidden by the Roman Catholic Church. It means trying to make the world end by bringing about the kind of things that seem to be prophesied in the Book of Revelation. In the 1980s, Ronald Reagan was accused of doing this because of the Cold War. Well, this is what’s worrying me right now: the Artemis program was looking ever more likely but we “know” that it can’t happen, because if it did it would make our current existence improbable. Therefore, events can be expected to intervene to prevent it and any other such events from happening, because we’re alive now and living on Earth rather than in space or on another planet. The more likely it becomes, the more drastic the event preventing it would have to be. We can be confident that no chain of events which leads to a high-population future off Earth can happen, but we don’t know why it won’t. Any extinction event is incompatible with future human beings being born and carries a high degree of certainty, so to speak, of preventing a “space future”. Nuclear holocaust, catastrophic climate change, pandemic, the Artificial General Intelligence apocalypse – any would be fine. We have what feels like an ever-lengthening list of apocalyptic scenarios.
There are ways in which both Apollo and Artemis could be predicted to happen. If they don’t lead to a likely expansion into space, they’re absolutely fine. Apollo was substantially a Cold War publicity stunt by the West, mainly the US, and could be expected not to lead to anything else. In fact, its scaling down and cancellation is possibly “predictable” simply because we’re still here. The same could apply to Artemis. If it’s just a pipe dream, it won’t happen. Also, if it’s hyped and does not in fact lead either to a permanent base or people going to Mars, we might also be safe. On the other hand, anything which looks like it’s going to lead to an open future of humanity living permanently off this planet immediately becomes improbable because of that, and the probability of that happening kind of retroactively “causes” events which prevent it.
This is not necessarily a pessimistic scenario. It simply means that if we have a long future, which right now seems very unlikely, it will be on Earth, and at no point will there be permanent settlements of fertile people in space or on other planets. It also suggests a rather weird solution to the Fermi Paradox – where are all the aliens? Maybe the solution is that everybody realises this and has a failure of nerve, so nobody takes the risk. On the other hand, it also suggests there is a Great Filter approaching. The immediate solution to the Fermi Paradox in this case is the very vague idea that something stops aliens travelling through space, assuming they exist. The obvious alternative is that there are no aliens. It would also mean that the Great Filter hasn’t already happened.
The Great Filter is the idea that sometime between the appearance of the simplest life to the existence of advanced interstellar civilisations, a significant barrier prevents them from reaching this stage. There are two major possibilities: it’s already happened and we’ve gotten through it, and it hasn’t happened yet but it will. It could be pretty benign. For instance, maybe everyone decides not to bother going into space because they want to solve social problems at home, become spiritually enlightened and lose interest in doing so. I’ve mentioned various attempted solutions on here, including the combined importance and scarcity of phosphorus, the possibility that we might just be swamped in a Galaxy teeming with civilisations, that everyone else might be really bad at maths or that we’ve committed some kind of faux pas that puts us beyond the pale. Another intriguing idea, and calling it a possibility may be going too far, is that civilisations get to the point where they discover backwards time travel and destroy themselves to the extent that they never existed in the first place or are automatically pruned by that very discovery. In a way, this might be the same as being that everyone else might actually be too good at maths: so good that they discover time travel using it and that causes them never to have existed.
The Great Filter could be divided into past and future, but there could of course be a third possibility: maybe it’s happening to us right now. Perhaps all our problems are combining together to wipe us out, or a specific event is occurring which is incompatible with us having a future of any kind.
But maybe Artemis won’t lead to an open space future. The plans after the lunar landing are vague and might not lead to anything much in the long term, so it could be a similar stunt to Apollo. The Chinese have a plan to build a base at the South Pole there too though, so the possibility of them making further plans could be considered. Another possibility is private enterprise taking over, but this might not be good. This is where I get into the whole “Up Wing” business, and maybe I shouldn’t go there. It could just be that due to the probabilistic argument, every attempt at a major space development project is destined to fail and Artemis is just one of those. The Chinese program is too, and all of this can be concluded by the simple fact that we’re around now, not having settled elsewhere in the Universe. It isn’t because of any particular reason so much as that our existence ends up selecting a future without space travel. It is, I’ve long thought, very odd that the predicted developments such as rotary space colonies and going to Mars did not come to pass, but maybe it’s just that if they had, the average human being would be someone living thousands of years in the future. If this is so, space exploration might simply look jinxed for no apparent reason. This does actually seem to happen in at least one particular case, referred to as the “Mars Curse”. Only 53% of missions to Mars succeed completely. This may not even be specifically because of something Mars does, as the flights have been known to fail before even leaving the atmosphere. Rather than adopting a superstitious approach, maybe it’s just because of probability: it scuppers the chances of humans getting there if we don’t find out enough about it, so that’s what happens.
If it really is true that the probability argument works, there seem to be at least two applications to prediction here. One is the Doomsday Argument in general, which appears to have fairly major flaws (for instance it might just predict the end of mortality or pessimism rather than the human race because it focusses on the births, but could be about the thought of extinction itself becoming extinct). Another is the possibility of eliminating an apparently plausible future, which may also connect to the Fermi Paradox. But might there not be other things which this kind of argument could predict? The Mars Curse could be a real thing which does not, however, have any causal or for that matter acausal explanation, but is just how things happen to be. It seems to me that this has potential, but it’s all rather imponderable.
Meanwhile in the real world, Artemis faces delays and constantly recedes from the near future, like the invention of efficient fusion power. What a surprise.
I’ve just heard an excellent podcast episode called ‘The 3 Body Problem Problem’, which you can listen to here. It’s very wide-ranging, and be warned, rather despair-inducing. I’m not going to go into too much depth about it, but I am going to talk about the Dark Forest Hypothesis in its social and political, and maybe psychological, setting, which is what that podcast already did.
The new Netflix series ‘The 3-Body Problem’ is an eight-part adaptation of 刘慈欣 (Liú Cíxīn)’s famous and award-winning novel, 三体, the first of a trilogy called ‘地球往事’, translated as ‘Remembrance of Earth’s Past’. In order to engage with this series in sufficient context, I feel like I’m going to have to zoom out so far that the actual trilogy itself is going to end up looking like an invisibly small dot on an invisibly small dot, and I don’t want that to happen so I’m going to have to break it down a bit. I am deliberately posting names and titles in 汉字 (Hanzi) because of the issues it raises. Two things about this: I am more used to Wade-Giles than pinyin romanisation and I prefer traditional Hanzi to simplified because the latter is trickier to associate with the ideas it represents. Looking at simplified Hanzi, which is what this is, is like having a migraine because there are bits missing from the characters which one really could do with being able to see. Yes this makes me a dinosaur, but non-avian dinosaurs would still be around today were it not for their “left hand down a bit” mishap 66 million years ago and there was basically nothing wrong with them.
I’ve read the first book of the trilogy. I didn’t so much not want to read the rest as find it an unnecessary financial outlay, so it ended there. Netflix too might end it there because they apparently haven’t had as much success out of this extremely expensive series as they’d hoped, so like several other series they may well cancel it way before time, while in the meantime adding lots of fluff to stories which were supposed to end like ’13 Reasons Why’, and while I’m at it, that book and series is interesting because it’s basically ‘An Inspector Calls’ for the twenty-first century and yet manages to be quite unfortunate in its implications regarding bereavement of people who have killed themselves (I don’t use the S-word because it’s not a crime). Anyway, before I get irredeemably off-topic I shall post a
Spoiler Warning!
and be done with it. So if you want to enjoy ‘The 3-Body Problem’, don’t read past here.
Before I get into the broader issues with the Netflix series and the book, I thought I’d explain what the Three Body Problem itself is. First of all, it’s fairly easy to work out where Cynthia (“the Moon”) and Earth are going to be at a given time, so for example we can easily work out when the phases happen, when it rises and sets, how far away they are from each other, when eclipses happen and how long lunar months are, and by extension the times of the tides. A lot of these things are also linked to Earth’s rotation, but the mathematics are fairly straightforward, although because both Earth and Cynthia move in ellipses relative to each other and the centre of mass (the “baycentre”) about which both orbit is not at Earth’s centre, and it would really help to know calculus, which I don’t, to make these calculations. Likewise with the Sun and Earth we know when the equinoctes and solstices are and how far away the barycentre of the two bodies is at any given moment to a high degree of accuracy. This is because Earth, Cynthia and the Sun and Earth are two bodies each when considered in that way. The fact that we can work out all this stuff in both cases also shows something else: that there are some straightforward pretty much accurate solutions for three bodies provided they’re in certain arrangements with each other. There are actually a lot of situations when the movement of three bodies fairly close to each other like the three mentioned here can be determined quite accurately. The case described here is simplified by the fact that Cynthia is both close to and much less massive than Earth and the Sun is much further away and more massive than either. Another very useful case is that of the Lagrange Points, where the balance between the gravity of two of the bodies is equal, leading to a stable point associated with them. Examples of this are sixty degrees behind or ahead of a planet or satellite in the same orbit, some cislunar point between a planet and its star or a planet and its satellite where the gravitational pulls are equal and cancel out, and some translunar point where the pull of Cynthia and Earth are again equal. As I’ve mentioned before on this blog, these points form a kind of “rapid transit system” around the Solar System which minimise the energy required to get between the various asteroids, moons and planets. There are other situations too. However, the Universe isn’t usually that neat and the majority of interactions between three bodies in fairly close proximity to each other are chaotic.
You really do need to look away now if you want to avoid spoilers.
The 三体 (Sān tǐ) are technologically competent aliens native to the Alpha Centauri system in the story. The Centauri system is in reality a ternary star system. Two Sun-like stars, one somewhat more massive and warmer than the other, orbit each other at a distance of between eleven and thirty-six times Earth’s distance from the Sun, whereas eleven thousand times the Earth-Sun distance, known as an AU (astronomical unit) from the barycentre orbits a much less massive red dwarf, Proxima, famously the closest star to the Sun except that since it takes half a million years to orbit the system so for some of the time it’s further from us than the other two, ignoring the fact that the entire system and the Solar System are both in their own orbits around the Galaxy. Right now, though, as its name suggests, its the closest. This situation, where two stars orbit each other much more closely than a third, is very common in the Universe and seems to be the most stable arrangement: the stars arrived in these positions after some chaotic behaviour and have now settled down. However, in 刘慈欣’s book, he imagines that a planet situated near these stars would have a chaotic orbit, some of the time getting too hot for complex life, sometimes getting too cold, sometimes being seriously perturbed by their gravity and sometimes almost being ripped apart by it and suffering severe volcanic eruptions. Life on such a planet could be imagined to be very difficult. It’s worth noting that this is not the real situation for most possible orbits of planets in the Centauri system, although it would be so for certain positions, such as for a planet halfway between the Sun-like pair or orbiting the Proxima far enough away to be strongly influenced by that pair’s gravity.
Due to the chaos of their home world, the 三体 decide to travel to Earth, and while doing so they also decide to harness the power of human intelligence by getting us to solve their world’s three-body problem through a VR video game where the player is put on the world in question, represented in a way humans can relate to, and has to find a solution to their predicament.
The first book, ‘三体’, begins in the 1960s during 毛泽东’s (Máo Zédōng’s) Cultural Revolution, where a scientist, 叶哲泰, is being denounced in a Struggle Session for his teaching of Einsteins Theories of Relativity. He is in fact killed in the process and his daughter, 叶文洁, is sentenced to hard labour followed by prison. This leads to her becoming very cynical about the human condition and our ability to improve things ourselves. Later on, she is employed as an indentured servant practicing science at a military base attempting to send and receive messages from any alien civilisations which might exist in other star systems, apparently focussing on the Centauri system. One day, she receives a message from an individual altruistic alien telling her that humans must at all costs cease to attempt broadcasting their existence and attempting to message aliens because it puts us all in danger. Because she now believes there is no way humans can sort out their own problems, 叶文洁 does the opposite, sending an enthusiastic message of welcome to the 三体, i.e. the aliens, and they proceed to plan to invade Earth, a process which will take four centuries because they can only travel at one percent of the speed of light.
There’s plenty more to both the series and the original trilogy, but this is enough to be going on with in terms of the details of the first book, and there is a particularly crucial point which is named after the middle novel of the trilogy: “黑暗森林”, or “The Dark Forest”. 刘慈欣 is not actually the first person to propose this idea.
Anyone who has read much of my blog will know that I think about the Fermi Paradox more than occasionally, but just in case you haven’t come across this, the Fermi Paradox, mentioned by the physicist Enrico Fermi in 1950 CE but not originally his idea, is this: the Universe is vast and there are innumerable Sun-like stars and planets orbiting them, and also æons old, so that life could have evolved from microbes to humans almost three times over or more given its age, and yet we hear nothing from intelligent aliens, are unaware even of the existence of life anywhere else in the Universe and have never been visited by them. In other words, “where is everybody?”. I’ve mentioned a few of the more interesting attempts at solving this problem in this blog. For instance, it might simply be that everyone else is really bad at maths and therefore there’s no rocket science on alien worlds, or it could be that the element phosphorus is always essential to life but is too scarce for it to happen very often, and when there are intelligent life forms, they can’t get out of their little oasis of phosphorus to reach other star systems, where in any case they’d have to take phosphorus with them to establish an outpost. One simple solution is that there’s no life anywhere else in the Universe at all. One I was keen on for a very long time was that other civilisations have something like the ‘Star Trek’ Prime Directive, that they can’t interfere with developing civilisations until they reach a certain stage of development. It could also be that there are plenty of civilisations which reach something like a twentieth century level of technological development but then end up wiping themselves out in a nuclear war, destroying themselves through climate change or developing artificial intelligence which then decides they’re a threat and kills them all. Note that I say “twentieth century level”: we could be living on borrowed time here.
Quite a lot of this is not at all reassuring. Perhaps even less reassuring is 黑暗森林, which is as I say not actually an original idea although it was 刘慈欣 who actually named it that. The exact metaphor was used by Greg Bear in the 1980s. The idea is this. There is silence out there because aliens elsewhere in the Universe are aware that broadcasting their presence would threaten their existence due to potentially hostile threats from other star systems, and humans are simply too naïve to realise what a bad idea it is to tell all and sundry we’re here. We don’t know any of them from Eve, and they could be really dangerous. They could just go, “ooh juicy, another race to enslave and another nice planet to conquer” and do something horrible to everyone. Another way of putting it: “it’s quiet. Too quiet.” It’s like the silence that falls over the clichéed hostile bar when someone from the Other Side enters.
Now I do not like this solution, to say the least. Obviously in saying that I could just be all weird about it and say, “well I don’t like this any more than you do, but facts is facts and it is what it is,” but that’s not what I’m saying. I might not like the course of a fatal disease or the policies of a particular political party, but it’s still possible to find that particular pathology interesting or the implementation of a particular set of policies fiendishly clever or elegant in a Machiavellian way. In this case, however, I see the solution itself as pathological, and apparently I’m not alone in that as you will find if you listen to that podcast. But I already had these misgivings before I heard it. The problem is that it’s very negative and cynical, which doesn’t necessarily make it unappealing, but more than that, it seems to be a reflection of the current state of the society, or perhaps world, in which it was written.
Because the thing is, ‘地球往事’ is horribly, horribly grim and oppressive feeling. Suppose you look up at the skies and you see stars, an infinite horizon, endless hope and possibility and most of all for me the feeling that the atrocities and Hell we’ve made for ourselves on this small blue dot is as nothing compared to the hope the splendour of this unknown Universe around us shows. Even if it’s devoid of life entirely, it’s still magnificent and majestic, and moreover in spite of the actual Three Body Problem as opposed to the book, most of it works for pretty much of the time in one way or another. And if it isn’t devoid of life, there’s the optimism and awesomeness of a Cosmos replete with possibilities of friendship and fascinating variety. “Infinite variety in infinite combinations” as the Vulcans say.
There’s hardly any point in saying this, but just because something is appealing doesn’t make it plausible. I might be looking up at the sky with foolish, immature and groundless optimism. Absolutely, that could be so, and it’s very hard to decide whatbecause of the silence we all experience from the vast emptiness that surrounds us. So I don’t like it, but more importantly, what do the myths we make up say about us? What does it mean that 刘慈欣, in the 中华人民共和国 (People’s Republic of China) of the twenty-first century CE, is able to get this idea out to popular culture in the West via Netflix? Were there obstacles placed in front of him by the 中国共产党 (CCP) difficult to overcome, or were they not placed there in the first place because he perhaps has a knack of saying what they want him to say? Is he an establishment or an anti-establishment figure, and what does it mean that Netflix are apparently happy to stream what might be 中国共产党 propaganda? Or is it universal in some way, and if so is that universality a good thing or a bad thing?
‘ 三体’ has also been adapted by 腾讯 (Tencent) into a very different version. I know about 腾讯 on a personal level because someone close to me worked in 中国 (the Central State, i.e. China) for some time and the only way we could send messages to each other was through their app, QQ. Now I didn’t trust QQ very much at all and I was careful what I said on it, and I believe that was justified. One way of looking at this is that I’ve been duped by Western anti-Chinese propaganda, but it’s not that simple. QQ is their social media. Our social media are about as trustworthy, and this is not at all to say that 中国共产党 is better than the global megacorps. It’s more that they’re equally bad. It’s not about not trusting 中国. It’s about not trusting any big faceless organisation of any kind, because they simply will not have the interests of the ninety-nine percent at heart. We all know this.
Getting back to the actual Three Body Problem as understood in physics, it seems fairly clear that 刘慈欣 uses it as a metaphor for how unrestricted social systems are chaotic and unpredictable. A laissez-faire economic or social system, or a liberal or social democracy is just such a chaotic system, but it can be simplified by totalitarianism. If the likes of 中国共产党 and 腾讯, i.e. a few large organisations with a high degree of control over society, exist, we no longer have a chaotic Three-Body Problem but at least a special case of the problem like that of the Lagrangian Points or the Sun and Earth. Society can be made sense of and predicted. Likewise, in the West we have something like the social media firms, able to socially manipulate us all, and the US Republican Party, greatly simplifying the West through that extreme degree of control and gaslighting. So Netflix will be fine with streaming ‘The 3-Body Problem’ and by clamouring for a second season, which I must admit I personally want, we’re actually saying yes please, let’s have some more of that tasty propaganda.
There’s more than this though. ‘Star Trek’, and even more so Iain M Banks’s ‘Culture’ series and Ursula K Le Guin’s ‘The Dispossessed’, all provide a hopeful mythos for the nature of the wider Galaxy and optimism for the future. To quote from Banks’s ‘State Of The Art’:
Here we are with our fabulous GCU, our supreme machine; capable of outgenerating their entire civilization and taking in Proxima Centauri on a day trip…here we are with our ship and our modules and platforms, satellites and scooters and drones and bugs, sieving their planet for its most precious art, its most sensitive secrets, its finest thoughts and greatest achievements…and for all that, for all our power and our superiority in scale, science, technology, thought and behaviour, here was this poor sucker, besotted with them when they didn’t even know he existed, spellbound with them, adoring them; and powerless. An immoral victory for the barbarians.
Not that I was in a much better position myself. I may have wanted the exact opposite of Dervley Linter, but I very much doubted I was going to get my way, either. I didn’t want to leave, I didn’t want to keep them safe from us and let them devour themselves; I wanted maximum interference…I wanted to see the junta generals fill their pants when they realized that the future is––in Earth terms––bright, bright red.
Instead of such a myth, we are now asked to adopt 黑暗森林 as the explanation for the silence of the heavens, and maybe beyond that to accept that that silence justifies fear of the Other, and through that fear, as occurs later in the trilogy, that totalitarianism is the only answer. Does that sound at all familiar? Does it perhaps sound like certain members of the Republican Party rejecting democracy and freedom of the press in favour of Project 2025? And yes, it most definitely sounds like something coming out of 中国, but it’s equally at home in the West, and I happen to be mentioning the US Republican Party here but it applies just as much to many other Western countries, including Britain.
You may have struggled with my incessant use of 汉字 in this post but all that really is, most of the time, is a way of transcribing ideas into ideograms like our &’s and @’s. Just as we might look over at that country and think that the Central State has essentially foreign ideas based on the thoughts of “Chairman” Mao, we might also imagine that the capitalist West is free from such things. But it isn’t. It suits the West just fine actually. Nor is the Central State in any wise Communist, because by definition any economy with a stock market isn’t Communist. It’s just as capitalist as we are and it’s actually better at it, to the extent that certain people could learn from them how to be even more capitalist than they are already. Oceania has always been at war with Eastasia.
We are aware that encounters between White people from Western Europe and racialised people elsewhere, such as in Afrika, the Americas and Oceania, have not generally ended well for the latter, and this has often been associated with a mismatch in technology. We might attempt to deduce that this is also what would happen if another species from elsewhere in the Universe with superior technology encountered humanity. However, that makes the rather major and unwarranted assumption that aliens are like us. This is unlikely, partly because they’re alien but also because in this scenario they’ve reached another star system. It also assumes that the greed and materialism dictated by the European-derived economic system is a law of nature and that there’s no other way things can proceed.
This, though, is how I see things going. Here we are on Earth with increasing threats to our civilisation, mostly self-inflicted, such as the use of weapons of mass destruction, anthropogenic climate change and artificial intelligence, among other more prosaic problems. In the meantime, we haven’t been back to Cynthia for over fifty years and there’s no sign of us building large space colonies or going to Mars. Hence we’re missing out on the Overview Effect, or Arthur C Clarke’s ‘Rocket To The Renaissance’, both of which could stand a good chance of changing global consciousness, we have no orbital solar power stations which could satisfy all of our energy needs and enrich Third World nations around the Equator, and various calamities could, and probably will, befall us which space exploration and settlement would’ve prevented. On the other hand, suppose a civilisation out there somewhere has thriven and got past this, or hasn’t got itself into such a pickle in the first place. Those are the kinds of civilisation which we’re likely to end up contacting, because the others simply aren’t viable. Which kind of civilisation we are remains to be seen to some extent, although I know which one I think we are. Or maybe every species of this kind just ends up annihilating itself.
The attempt to contact aliens depicted early on in this series and book is an act of hope, of optimism, which is depicted as bringing down utter catastrophe upon the world. Well no, I’m not going to adopt that view, particularly when it seems to suit certain social forces exceedingly well. I prefer the other. Hence if technological cultures exist elsewhere, they would be of the following kinds: unable or unwilling to leave their planet and perhaps quite healthily uninterested in doing so, in which case they’re not a threat; capable of space travel but also wiping themselves out before leaving their solar system, and yes those would be hostile but are not a threat; able to leave their systems but unwilling to contact us for various reasons; able to leave their systems, peaceful, coöperative and friendly. Or, there could just not be any intelligent life anywhere else. Any of these options has nothing to do with the Dark Forest, is more inspiring than that and is less likely to be useful for political oppression. So there!
If you go back to where I started this series properly, you’ll find that I produced a post, whose name and location I’ve currently forgotten, introducing the Solar System from the outside in. I’ve now returned to the outermost part of the system except for the Oort Cloud, and I ask myself, are these outer reaches really dull? Well, they are in a literal sense of course, in that the Sun is pretty dim at this distance, but the wide separation, small size and low temperature of worlds, if that’s the right word for them, combined with the facts that nothing has ever visited them and that they’re hard to detect, means that they might also be exceedingly boring. I can imagine people travelling to them who want to get seriously away from it all, and from other people. In fact, there’s a scene in an Iain M Banks novel about someone who has done precisely that. I think it’s ‘Excession’.
There’s a lot going on in the regions near the Sun, and I use “near” quite loosely as I intend for it to apply to Jupiter and Saturn, the latter being well over a milliard kilometres from it. Incidentally, why is it we get stuck at kilometres? I’ve just fished out an obscure English word to describe a distance which could easily be referred to as a terametre, and yet we never say that. The further out one goes, the less is happening, with the occasional exception such as Triton’s liquid nitrogen geysers and the mysterious brightness of the surface of Eris. Average distances between worlds increase, temperatures plummet and the Sun looks ever dimmer. That said, it’s still possible, for example, to imagine a world so cold that it has oceans of helium II which crawl over its surface and climb mountains, or outcrops of superconducting alloys which generate incredibly powerful magnetic fields. I don’t know if either of those things are possible, because the 3K background temperature of the Universe might rule them out and helium only becomes superfluid at 2.17K, but there have always been surprises. Few people would’ve guessed that Neptune has winds which blow faster than the sea level speed of sound, for instance. Perhaps high winds on a very cold planet would cool it below the temperature of deep space.
Considering the history of the Universe, a frantic and hyper beginning slows down continually, through the current stelliferous era and other less and less eventful stretches of time until basically nothing is happening. Space is rather like this too. Not a lot goes on in the Oort Cloud.
Even so, there is stuff out there. For instance, there’s a planetoid nicknamed FarFarOut, which is 132 AU from the Sun. Also known as 2018 AG37, FarFarOut is about four hundred kilometres across, which means it could be round. It actually swings round to being only 27 AU, closer than Hamlet. It takes 718 years to orbit and at its maximum distance of 132.7 AU the Sun is almost 18 000 times dimmer than from here. There’s also 2019 EU5, which averages 1 380 AU from it and has a maximum distance of 2 714 AU. These figures are highly uncertain, but if the aphelion is correct (it could be considerably greater or less), sunlight at such a distance is finally weaker than our moonlight and the planetoid takes fifty-one thousand years to orbit the Sun at a mean velocity of about eight hundred metres per second. With such planetoids, it becomes difficult to judge their actual trajectories because they move so slowly and haven’t been observed for long.
There are now five human-built spacecraft out there: Pioneers 10 and 11, Voyagers 1 and 2 and New Horizons, the last being the newcomer, only launched in 2006. Voyager 1 was manœuvred out of the ecliptic so it could get a good view of Titan, and is therefore heading out into the scattered disc rather than the Kuiper belt. It’s 153 AU from the Sun at the moment. Voyager 2 is 130 AU out. Both were launched in 1977. The Pioneer probes have been going for rather longer but are actually closer, at 129 and 108, but they’re all now over twice as far away as Pluto ever gets. New Horizons is a mere 50 AU from the Sun right now. Now a viable claim is made that the Voyager and Pioneer probes are now in interstellar space because the pressure of the solar wind is weaker than the ambient “flow” (I suppose) of charged particles between the stars, but there are still planetoids orbiting out there, even ones which never dip into the volume inside the heliosheath. Isaac Asimov’s novel ‘The Currents Of Space’, though its science is out of date, uses the idea of similar flows as an important plot point, so this is one possible way in which the outer part of the Solar System might not be boring. Processes taking place within the heliosheath which influence planets, asteroids, moons and so forth would not operate beyond it. For instance, any magnetospheres which exist out there would not be thrown into asymmetry by the solar wind, and larger and denser atmospheres could exist out there, although the only elements able to maintain a gaseous state at such temperatures would be hydrogen and helium, and in fact ultimately helium. It also means the useful isotopes found in lunar regolith would be absent from many trans Neptunian objects and this reduces the utility of mining for them.
There are a dozen known planets, dwarf planets by the IAU definition of course, which reach 150 AU or more from the Sun. This is one motivation for not calling them planets. If they were, they’d now outnumber the major planets. The same is, though, also true of asteroids and centaurs, and asteroids were simply called “minor planets”. The whole thing seems a bit silly and solves a “problem” which had in any case already been sorted when such concepts as major and minor planets, or planetoids, were invented to address the issue after the discovery of Ceres, in the early nineteenth century CE. Right: I’m going to resolve not to go on about this for the rest of this post as I’m sure it’s getting old. These objects include Haumea, Quaoar, Eris, Sedna, Makemake, Albion, Gonggong, Pluto itself, Varuna, Arrokoth, Arawn, Chaos, Ixion and Typhon. Others are also named, but most don’t come up much in discussions or news, and most of them have provisional designations. To be honest, some of them just stick in my mind because of their names, particularly Quaoar but also Makemake and Gonggong. FarFarOut has a predecessor which isn’t so far out called FarOut. There are two zones: the Kuiper belt, which consists of objects orbiting near the plane of the inner system, and the Scattered Disc, comprising objects whose orbits are more tilted. The second category developed because of the gravitational influence of the outer planets, although it occurs to me that this might also be the region where the Sun’s influence and the traces of the solar nebula become less relevant to them. There is also a third region, the Oort Cloud, which is in really deep space beyond either of the others, whence some comets originate, and extends for over a light year in every direction. TNOs are also distinguished by colour (Eris springs to mind but that’s a special case as far as I know). They’re either steely blue or bright red. A classification kind of cutting across this are the poorly-named “hot” and “cold” categories. Cold TNOs orbit close to the ecliptic and are usually red. Hot TNOs have tilted orbits and range between the two colours, which means that the red ones are the “cold” ones.
One of the weirdest known trans Neptunian objects is Haumea, illustrated above. This has three remarkable features. It has a ring, two moons and is ellipsoidal but far from spherical. It counts as a dwarf planet. Its unusual shape is called a Jacobi ellipsoid, and is rather surprising. It intuitively makes sense that a rapidly-spinning body would be thrown outwards at its equator and therefore assume a kind of tangerine shape, or perhaps even a discus shape, as seen clearly with Jupiter and Saturn but also with most major planets including Earth to some extent. Venus and Mars are somewhat different, the former being almost spherical and the latter having a more egg-shaped form due to the Tharsis bulge. This more intuitive shape, an oblate spheroid, is quite common and the torus is another quite remarkable stable shape which, however, is hard to envisage actually forming in the first place. There is a notorious (to Sarada and me) pebble classification system called Zingg (two G’s), which divides them into spheres, discs, rods and blades according to their X, Y and Z axes. This used to be a source of joy to us due to its apparent obscurity, but has its uses, and Haumea counts as a blade. Each axis is markèdly different to the other two. Lagrange, who discovered the points of gravitational equilibrium around pairs of masses responsible, for instance, for the trojan asteroids in the orbits of several major planets and the trojan moons in the Saturnian system, held that the only stable shape for a rapidly rotating body of a certain size was the oblate spheroid, but counter-intuitively, this turns out to be wrong. This is the gateway to a whole branch of geometry involving ellipsoids.
Haumea’s axial dimensions are 2 322 × 1 704 × 1 138 kilometres. It spins once every three hours and fifty-five minutes, which is particularly high considering its size. Comparing it to Pluto, for example, that planet takes six and a half days to rotate and has a diameter of 2 377 kilometres. Not only is Haumea considerably smaller and less massive but it also spins three dozen times faster, causing a much stronger centrifugal effect. I have to admit that not only is it entirely unclear to me why Haumea is this shape beyond the simply fact that it’s spinning really fast and has thereby had projections drawn out from it, but also I can’t understand the maths behind it. If this can happen once, maybe there are larger planets out there somewhere with the same shape, maybe even Earth-sized ones. It seems unlikely, at least because a larger object would tend to be more spherical, although there could be other reasons why it might happen such as a nearby massive body pulling it out of shape. Haumea was probably hit some time in the past by something which sent it spinning wildly. It also isn’t clear that it’s reached hydrostatic equilibrium although it’s very large for a solid object if it hasn’t.
Haumea is the Hawaiian goddess of fertility and childbirth. The planet’s moons are named after her daughters, Hi‘iaka and Namaka. It’s thought to be rocky with a surface layer of water ice and seems to have a red crater near one of the geometric poles (i.e. on the equator). I’m guessing the reddish colour is due to tholins. Haumea seems denser than most other Kuiper belt objects, including Pluto, and may be as dense as Mars or Cynthia. It has crystalline water ice on its surface even though its temperature ought to cause the ice to become glassy. There may also be clay on the surface, and cyanides of various kinds. Hence the very surface would often be highly poisonous to ærobic life forms, including humans. There is no methane, suggesting that it was boiled away in the heat of impact.
The ring spins once every twelve hours, in other words a third as fast as the planet. The moons are small and probably result from the collision. Another thing which probably results from the collision is the Haumea family. In other parts of the Solar System, there are various families of objects, for instance the Vesta family, which consists of Vesta plus the asteroids which have been chipped off it, including some meteorites which have arrived on Earth. The Haumea family is the only identified group of objects beyond Neptune, and originates from the collision. They’re all water-ice at the surface and are fairly bright. Some may be up to seven hundred kilometres in diameter and count as dwarf planets in their own right. They average between forty-one and forty-four AU from the Sun. One of them seems to be in the family but is red.
Haumea itself is 43 AU from the Sun on average and has an orbital eccentricity of a little under 0.2. It takes 283 years to traverse this orbit, so it isn’t enormously further away than Pluto and in fact it gets closer to the Sun than Pluto does.
Another name which sticks in the mind belongs to the dwarf planet Sedna. This is one of the reddest known objects in the system and is also tied with Ceres in being the largest moonless dwarf planet. Sedna is one of those planets which makes me wonder whether it’s one of many undiscovered ones, because it was discovered due to happening to be almost as close as it gets to the Sun at 76 AU. Even that distance is almost twice Pluto’s. It takes 11 400 years to orbit the Sun and gets out to five and a half light days from it. The last time it was there, there were mammoths on this planet and the pyramids had yet to be built. It’s around a thousand kilometres in diameter, like Ceres. It’s named after the Inuit goddess of the sea and its denizens. The extremely elongated orbit, which has an eccentricity of almost 0.85, could be explained by the presence of an extremely distant and large planet. It’s part of a class (as opposed to a “family”, as in the Haumea family) of objects whose perihelia are greater than 50 AU and mean distances over 150 AU from the Sun. These orbits have an eccentricity of around 0.8, so although that’s the definition, in actual fact they’re considerably more elliptical. It’s been established that there are no large planets in the system beyond Pluto to a considerable distance, although there is the question of a missing ice dwarf. That would, however, not be detectable by current methods and wouldn’t explain the sednoid bunching of orbits. It’s also been suggested that the sednoids move thus because they were influenced by nearby stars back when the Sun was young and part of a cluster of baby stars. There are occasional stars which seem to be almost twins of the Sun due to similar proportions of heavier elements (often referred to in astrophysics as “metals”), suggesting that they were once our companions. Alternatively, they may have been captured from those stars early on in the history of the system. The other two objects falling into this category are Leleakuhonua and 2012 VP113.
As well as the usual tholins, Sedna is covered in frozen nitrogen and methane, which is present generally but absent from Haumea, probably due to the collision. Its orbit looks like this to scale:
There may be amorphous carbon on the surface. Unfortunately the term “amorphous carbon” is ambiguous as it can mean charcoal- or soot-like carbon, which in fact consists of graphite sheets haphazardly arranged, or it can literally mean amorphous, i.e. glass-like, carbon, which might have special properties such as being a high-temperature superconductor and being harder than diamond. I suspect they mean the former – just a load of boring old black gunk like you might dig out of a coal mine.
Sedna is special because it isn’t. It’s probably an example of a very numerous class of objects orbiting way out beyond the influence of Neptune in the Oort Cloud. We happen to know it’s there but there are likely to be many, many more examples way outnumbering the objects known in the inner system whose orbits haven’t so far allowed us to detect them. That said, the presence of tholins is related to the influence of solar radiation so it might not be typical of them.
Another planetoid is Arrokoth, unique in being the only trans-Neptunian object other than Pluto-Charon and their moons to have been visited by a space probe, New Horizons. It was nicknamed Ultima Thule, but this was later deprecated due to the association with Nazi occultism. It was actually named in a Pamunkey ceremony. The common “dumb bell” appearance shared by two of Pluto’s moons, some comets and other objects is also seen here. It’s thirty-six kilometres long altogether but consists of two smaller fused planetesimals, fifteen and twenty-two kilometres in length. Planetesimals are the bricks which make up planets and moons, and have never been seen in their raw form before. If a twenty-kilometre object is typical, Earth would be made up initially of over a hundred million of them, having long since melted together and lost their identities. There are interesting substances on its surface, including methanol, hydrogen cyanide and probably formaldehyde-based compounds and complex macromolecules somewhat similar to those found in living things. The basin in the foreground, which is probably a crater, is a bit less than seven kilometres across and called Sky. The axis of rotation passes through the centre of the dumb bell.
Arrokoth is a “cubewano”. These are named after their first discovered member, 1992 QB1. Also known as “classical Kuiper Belt objects”, cubewanos are often in almost circular orbits less than 30°from the plane of the Solar System, but are also often not. They have years between 248 and 330 times ours, the lower limit being defined by the plutinos with their sidereal periods close to Pluto’s. I’ve mentioned them above. They’re distinctive in not being particularly distant (relatively) and also not having orbits connected to Neptune’s.
Quaoar is a particularly large cubewano. Its name is from an indigeous people called the Tongva in Southwestern North America, although for a time it was called “Object X” as a reference to Planet X and because its nature was unknown. You can see the planetary definition crisis developing here, as it was discovered in 2002. It was first imaged in 1954, but like many other bodies went unnoticed for many years. It takes 289 years to orbit the Sun and is 43 AU from it. It seems quite dark, suggesting that it’s lost ice from its surface, which has a temperature of -231°C. It has a moon to keep it company, like many other trans-Neptunian objects. The diameter is around 1 100 kilometres.
Previously, the largest known TNO was Varuna, discovered in 2000. This may also be a “blade”-shaped planet like Haumea, and is just barely beyond Pluto’s average distance from the Sun at 42.7 AU, taking 279 years to orbit. It seems to be less dense than water and its average diameter was recently estimated at 654 kilometres. It takes six and a half hours to rotate on its axis.
I feel that this series is now drawing to a close. However, there are many objects I haven’t considered, such as the Neptune trojans, the possibility of Nemesis and the question of what large objects may be swimming out there in the depths of the Oort Cloud. There is also one planet I haven’t given its own post. It’s a small blue-green planet, third from the Sun, and will form the subject of my next post.
For Neptune, or rather knowledge thereof, the early 1970s CE were a simpler time. In fact any time between 1949 and 1989 was a simpler time. Back then, Kuiper having discovered Nereid, a smaller and peculiar moon, at the end of the ’40s, Neptune only seemed to have two moons: Triton and Nereid. This state of affairs continued until the end of the ’80s, which was approximately one Neptunian season. Four decades during which the planet only appeared to have two moons. I’ll start with that.
I’ve already mentioned Triton, the oddball moon of the Neptunian system two hundred times as massive as all its other moons put together, orbiting backwards and at an angle, in an almost perfectly circular trajectory. I haven’t mentioned the equally oddball second moon discovered, Nereid, and I say the early ’70s were a simpler time but in fact its own orbit is very peculiar. Nereid has the most eccentric known orbit of any moon. It sometimes feels like discussing the orbit of a celestial body is a bit tangential to the core of its nature, but orbits have important consequences for the nature of planets, moons and their neighbours, and in this case it’s so odd that it would be strange not to mention it, particularly back in 1971 when that was practically all that was known about it. It sometimes feels like the Solar System “frays at the edges” with all this stuff, because things out here are really quite outré compared to the relatively regular innards of this system we call solar. Nereid’s orbit is entirely outside Triton’s, approaching Neptune by 1 353 600 kilometres at its closest and moving out to a maximum of 9 623 700 kilometres distance from the planet. It takes five days less than a year to go all the way round, which is appealingly similar to Earth’s sidereal period. In fact of all Solar System objects its year seems closest to ours. No other moon is remotely as eccentric. At its closest, Neptune would be a little larger than the Sun is in our own sky, and at its furthest, six months later (so to speak), about the size of a lentil on one’s dinner plate. This is probably the result of Triton’s capture, which to me suggests there are other former moons wandering far beyond Pluto or even in interstellar space, or maybe in the “Gap“.
Nereid is small and grey. There is no good image. The best one is this:
Not very impressive, eh?
Unlike Triton, Nereid orbits in the usual direction, as do two other irregular moons Sao and Laomedea, further out. Another moon, Helimede, is a remarkably similar colour but orbits the other way. It’s considered to be a bit that chipped off of Nereid. Nereid itself is about 360 kilometres across on average and may be somewhat spherical but by no means perfectly so. It’s one of several bodies in the system which are right on the border of being round, and is almost as large as the definitely round (sans Herschel) Mimas, but also rather denser. Its shape is therefore hard to determine. Certainly its gravity would be sufficient to pull Mimas-like material into a spheroid, since it’s higher, but that very density may result in the moon being tougher and more able to support its own weight without collapsing. However, its variation in brightness probably means it’s quite irregular in shape and closer to Hyperion in form. Its colour is markèdly unlike that of most centaurs, and it’s therefore probably a “native” Neptunian moon. There’s water ice on its surface.
Proteus is the one which really surprised me. On the whole, the Voyager probes and others only discovered small moons, although Charles Kowal’s discovery of Leda skews that for the Jovian satellites because it’s unusually small for a telescopic discovery of that time. Proteus is actually the second largest Neptunian moon, being somewhat larger than Nereid, and is shown at the top of this post. It orbits the planet at 117 647 kilometres from the barycentre on average in a fairly round orbit, though nowhere near as round as Triton’s. It can be determined not to be perfectly spherical and is in fact not even particularly rounded, with dimensions of 424 x 390 x 396 kilometres. Its surface consists of a number of planes (or plains) with sharp angles between them at their edges and it’s uniform in colour, being somewhat reddish like many other outer system worlds. It was discovered by Voyager, but two months before the space probe got to Neptune.
Unlike Nereid, Proteus was close enough to Voyager 2 to be mapped. As can be seen above, it’s heavily cratered and its surface is therefore likely to be quite old, meaning that nothing much has happened to it in a long time. NASA also had a very steep “learning curve” with Proteus compared to Nereid as it went from being unknown to being mapped within a few weeks, whereas Nereid’s existence has been established for six dozen years now and still there is no map available except possibly the kind of vague albedo feature map which used to be done for Pluto before a spacecraft got there. It can also be seen through the Hubble Space Telescope. It’s fairly dark, probably because its surface consists of hydrocarbons and cyanides. The only named feature on its surface is the relatively large crater Pharos, 260 kilometres across, but due to its somewhat irregular shape this fails to give it the “Death Star” appearance Mimas has. Proteus is also receding from Neptune due to tidal forces and is now eight thousand kilometres further from it than when it first formed. Unsurprisingly, given that it was undiscovered for so long, it’s a lot darker than Nereid.
The inner moons generally are coated in the same material as Proteus. A couple of them are quite notable. For instance, Larissa, which is 194 kilometres in diameter, was accidentally observed passing in front of a star in 1981, leading to the correct but unwarranted conclusion that Neptune has rings. The chances of a moon of that size being seen to cover a star are very small just anyway, but in Neptune’s case it’s even less likely because it moves against the “fixed” stars so slowly, taking almost three months to cover a distance equivalent to the face of the Sun. Larissa’s period is about twelve hours and it orbits only 73 400 kilometres above the centre of Neptune, putting it close to the Roche Limit, where large bodies are torn apart by gravity. It was, however, given a provisional designation in ’81, namely S/1981 N1, so it was accepted as a moon back then. Like the other inner satellites, it’s likely to be a rubble pile, without enough gravity to pull itself together as a solid object. It may be a future ring.
Another somewhat interesting moon is Hippocamp, which is so dim Voyager failed to notice it and had to wait for the Hubble Space Telescope to discover it, which was done by the combination of a number of images as even then it was too faint to be spotted. It seems to reflect less than ten percent of the light falling on it. It’s only seventeen kilometres across.
The closest moon to Neptune, and in fact to any solar gas giant at all, is Naiad, taking only seven hours to travel round the planet. It’s quite elongated at eight by five dozen kilometres, and will either become a ring or fall into the atmosphere in the relatively near future. Thalassa, the next moon out, is coörbital with it. Their orbits are only eighteen hundred kilometres apart but they never approach that closely because they move north and south of each other as they orbit, putting them a minimum of 2 800 kilometres apart. It’s about the planet’s radius from the cloud tops, making Neptune occupy most of its sky. This would make the surface look deep purple if it has a reddish coating like the others.
Like some other moons, the naming scheme has the prograde moons end in A, the retrograde in E and the highly tilted in O. The two outermost moons, Psamathe and Neso, are relatively close to each other, and stand in contrast to Naiad by being the most distant moons of any known planet at forty-six and fifty million kilometres. Neptune’s lower mass also gives them exceedingly long years of around a quarter of a century.
The outermost of the planets known in ancient times, Saturn was traditionally considered the limit of the Solar System, a symbolism reinforced by the fact that it has a restrictive-looking set of rings around it. Oddly, Saturnine herbs are partly distinguished by having prominent rings, among other things, even though the association with the planet pre-dates their discovery.
Saturn is a couple of things. It’s the most squashed planet. It’s like it’s been “sat on”. Geddit? Seriously though, it’s flattened to the extent that its polar diameter is 9.8% less than its equatorial. This isn’t as obvious as Jupiter’s because the ring obscures its shape and seems to cause an optical illusion that it’s rounder than it really is. There are two reasons for its oblateness. One is that it spins very fast, with a day of roughly ten and a half hours. It’s difficult to be precise because like Jupiter it doesn’t rotate as a solid object would but has several “systems”. The other is that it’s also the least dense planet, also making it the softest. It’s actually less dense than water. If it were possible to put a tiny version of Saturn in the bath, it would float like a rubber duck. Its average density is only 69% that of water, which is lower than any solid element except lithium. It even looks like it’d make a good pool toy or floatation aid.
According to the Ætherius Society, Saturn is where the Interplanetary Parliament, er, sits. The beings who rule over this Solar System are said to be enlightened golden spheres twelve metres in diameter. However, not many people agree with the tenets of that religion and reject the idea outright. I have no idea why they think this, but in general the religion is a lot less harmful as some other “flying saucer religions”, so to speak.
Before Voyager’s time, Saturn’s rings were divided into three, with actual gaps as well. There was the A ring, on the outside, split by Encke’s Gap which is about 325 kilometres wide, but the most obvious gap is the Cassini Division, 4 800 kilometres in width. An Atlantic-sized gap. The area this gap surrounds is the B ring. Both of these rings are opaque, but an inner ring, known as the “Crêpe Ring” is partly transparent and objects can be glimpsed through it. When the Voyagers got there, unsurprisingly the rings turned out to be a lot more complex than that, and in fact they look more like the grooves on a record, not in terms of spirals but because there are hundreds of concentric rings. There was previously a plan to send the Voyager spacecraft through the Cassini division but it turned out to have plenty of rings within it itself. Encke’s Gap contains a braided ring and a moon which has been called Pan.
Saturn is one of four planets known to have rings, but until the late 1970s CE it was considered unique in this way. This changed when a star in front of which Uranus was passing appeared to blink on and off at the same intervals on either side of the planet, and within a couple of years the Voyagers were able to photograph those rings while the spacecraft were near Saturn. Even still, Saturn’s rings are by far the most spectacular and brightest, the cleanest in fact. Saturn is in general positively gleaming, bearing in mind it only gets one percent of the sunlight Earth does per square metre. This isn’t as dingy as it sounds because the human eye would adjust easily to that without there being any obvious difference after a while. Speaking of dinginess, like the rest of the system Saturn is overshadowed by Jupiter. It’s smaller and further out, and as far as we’re concerned also further away. Thus before anyone was able to point a telescope at it, apart from being on the edge of the system it was relatively dim and insignificant. It’s still brighter than first magnitude and doesn’t vary much on account of it being ten times our own distance from the Sun, meaning we observe it as between nine and eleven AU away, making a difference of only around a third, and because it’s a superior planet we never see it as a crescent and it’s nearly full most of the time.
The rings are extremely thin compared to their width at around fifty metres, and since Saturn’s axis and orbit are both tilted with respect to Earth, they are sometimes more visible than at others. This confused the first astronomers to observe the planet through telescopes because it meant the features they appeared to be able to see changed shape and size and even completely disappeared. The earliest such observer, Galileo, thought he saw two spheres accompanying it on either side, which incidentally he referred to as “planets” (in Italian or Latin presumably), showing how the concept of planet changes over the centuries. This was in 1610. Soon after, others were able to see the rings but were baffled by their sudden disappearance until they realised it was because we were seeing them edge on. This range of angles would also apply to the moons, and rather annoyingly to anyone who might be visiting, all the larger closer moons orbit close to the plane of the rings and you wouldn’t really be able to see them. Only Iapetus, whose orbital inclination is 15°, has a good viewing angle and unfortunately it’s also quite far out, so Saturn would look nice but it wouldn’t dominate the sky like it does closer in. While we’re on the subject, Saturn is likely to be invisible from Titan due to constant thick cloud cover, but it would show the rings a little. Maybe if you were there you could set up a sightseeing service to take tourists above the clouds and look at the ringed planet.
In a sense, Saturn’s rings extend all the way down to the atmosphere, meaning that there must be constant meteor showers at the equator. I don’t know how this would be replenished. Maybe it can’t be and that’s why the Crêpe Ring looks like that. They reflect more light than the cloud tops and are edge-on to us at alternate intervals of thirteen and three-quarters and fifteen and three-quarters years due to the eccentricity of the planet’s orbit, which is 5.2%, thrice ours. The Crêpe Ring is also known as the C Ring and there are a number of others, although many would best be thought of as groups of much smaller rings nowadays. There’s the even fainter D RIng, which is inside the Crêpe Ring and ends around seven thousand kilometres above the cloud tops. The outer edge of the A Ring, beyond the Encke Division, is split into more widely separated narrower rings and there are three moons orbiting near them. The largest, or rather least small, of these is the F Ring, near another moon. All of these are called “shepherd moons”, which of course is also the name of an Eithne album, and they keep the particles in place in the rings. There are also coörbital moons, which swap orbits regularly.
The G Ring starts 2.8 radii from the centre of Saturn, which places it beyond the Roche Limit of 2.44, within which large objects would be unable to hold together. The main part of the rings is somewhat within the limit, but doesn’t extend right up to it. D and G can only be seen from forward-scattering light, and D is also drowned out from here by the planet’s glare. From the other side of Saturn both of them are easier to spot. In fact the progress of the four Pioneer and Voyager probes beyond the planet made it possible to see the rings from the other side for the first time, and also send signals through them to see how they were altered by and interacted with the ring materials, like shining a light through fabric to inspect the weave. This enabled scientists to determine that A, B and the Crêpe Ring are all water ice and that the range of particle sizes was between micrometres (able to scatter visible light) and decametres (the size of a double decker bus or so, able to scatter RADAR frequencies), but are mainly at least a few centimetres in diameter. Thus the material consists substantially of roughly snowball-sized chunks of water ice, although it can be much larger or smaller.
D may go all the way down to the cloud tops, although presumably this would make it unstable. It’s more of a region than a ring. The Crêpe Ring has grooves like the rest of the ring system, but they don’t correspond to gravitational resonances as might be expected. It also has two gaps, one 270 kilometres, or about the distance between Inverness and Dumfries, and another variable gap, more elliptical, between thirty-five and ninety kilometres wide.
Either side of the rings for about sixty thousand kilometres is a very thin cloud of hydrogen at a density of about six hundred thousand particles per litre. This is probably liberated from the ice in the rings by radiation.
The B Ring is redder and it’s been guessed that this is due to iron oxide, but I can’t help thinking it’s more likely to be tholins, but maybe it’s just me. It just seems like Saturn isn’t dense enough to have loads of iron available to do something like that, although that might depend on where the rings came from in the first place. But then, I’m not a scientist and iron does turn up in odd places sometimes, such as in Martian soil even though Mars is the least dense rocky planet. What do I know, eh?
B and the Crêpe Ring have a sharp boundary. There’s no gradual attenuation into the translucence. It just happens. The
The Cassini probe detected spiral ripples in the inner rings which are attributed to currents in the interior of the planet having a gravitational influence on the particles. Interestingly, these clumps and sparse areas are reminiscent of the arms of a spiral galaxy for me, which amount to “traffic jams” and are more like sound waves moving through the rings than permanent structures. Hence there’s a disc with spiral grooves associated with sound waves. Remind you of anything?
There are also spokes, which are harder to explain. These are dark radial features stretching across the rings upwards from Saturn, which maintain their integrity as they move around the planet. I may or may not have mentioned them in connection with plasma at some point. The reason this is odd is that one would expect them to smear out along the rings’ circumference because objects orbiting further out should be moving more slowly, hence the words “move around” rather than “orbit”. It’s thought that they’re held together by electrostatic charges. They persist for twenty to thirty hours and seem to be subject to the rotation of the magnetic field, as they rotate with the planet, unlike the rings generally. After this period they start rotating with the rings orbitally, which causes them to disperse. They’re found in the B Ring. Their relatively small size when they form suggests the fluctuations in the magnetic field are local and short-lived, lasting no more than a few minutes.
Attempting to write about the rings raises another issue. Looking at Saturn with a pole at the top tempts one to believe they’re horizontal, once again like a record sitting on a turntable (now I’m wondering if there are vertical record players), but in fact the A ring is above the Crêpe Ring rather than beside it. The spokes might be thought of as clouds of particles hovering above the rings but they are actually north or south of them. This would mean that when they return to orbiting around the planet, they will tend to move away or towards the equator, which is tantamount to moving away from or towards the rings, and all would move towards them within a period of around six hours and become lost among the fragments.
They also fluctuate in thickness over a period of hours, which can be seen in time lapse films of the rings in close up. This seems to be caused by the presence of satellites within the rings, or within other rings, and is possibly tidal.
The biggest apparent gap, visible from Earth through a good telescope, is the Cassini Division. Although it was thought to be empty before probes were sent there, it turns out to have about the same density of material as the Crêpe Ring, so the plan to send a probe through it would’ve led to the spacecraft being destroyed. It’s slightly elliptical and the width of North America, so like Galileo Regio on Ganymede it emphasises the sheer scale of the system that we can barely see it from here. Although it’s elliptical, varying by 140 kilometres in width, it’s centred on the centre of Saturn rather than being at one focus. I should probably explain this. According to Kepler, planetary, and in fact satellite, orbits are elliptical with the Sun at one focus. There was a notorious mistake on the last English pound note where one of the orbits shows the Sun at the centre rather than a focus, which will illustrate what it means:
It can be clearly seen that the largest orbit is centred on the Sun whereas the smallest is off-centre, as it should be. Then again, maybe the kind of people who forge notes are really obsessed with astronomy and would accidentally correct it! If you draw an ellipse using a loop of string secured to paper with two drawing pins and a pencil to draw the outline, the pins will be at the foci. The reason the Cassini Division doesn’t show this, I think, is related to emergent effects related to the collision of particles within the rings, but this is my guess. The spokes, as I mentioned, also don’t conform to Kepler’s Laws. All that said, the actual position of the Cassini Division does seem to be determined by the orbit of Mimas, the closest large moon, as the outer edge of the B Ring, which is where the Division starts, has a period of exactly half of that body’s.
The other gap visible from Earth is the Encke Division, which is somewhat further out and seems to be part of a general breakup in the integrity of the rings at the outer edge. It’s towards the edge of Ring A. When Voyager 2 was leaving for Uranus, the star Dschubba passed behind (i.e. in our direction) the rings and was eclipsed several times as the Encke DIvision passed in front of it, so there are several ringlets within the gap, and also some are eccentric.
Due to the grooved appearance of the rings and the fact that the gaps are not actually empty, the idea of orbital resonances causing them doesn’t quite work because whereas there’s a threshold from Earth observation which assigns some parts of the rings to gaps and others to, well, “ring”, this is not the situation observed near Saturn itself, and there are too many rings for orbital resonance to be the only explanation for this. My personal feeling is that the rings seem to have their own special case of physics in a similar way to how Earth’s land surface has. Here on Earth, we expect moving objects to slow down and stop on most flat surfaces and for heavier objects to fall faster than light ones, among other things, and some people tend to generalise that to the Universe in general, where it won’t work. Likewise, the presence of multitudinous ring particles, colliding with each other and becoming statically charged and repelled, among many other things, seems to lead to a special environment not at all like Earth but also unlike an ordinary orbital environment such as is found around Jupiter. Although there are other ring systems, they are nowhere near as dense and spectacular as Saturn’s. This doesn’t answer the questions in detail, but in a way it would be surprising if it did behave intuitively like a load of bodies obeying Kelper’s Laws because there are just so many of them. One idea is that there are density waves triggered initially by orbital resonances, but which then ripple outwards under their own momentum, creating the LP-style pattern we see.
As I recall it, there used to be two theories about what the rings were composed of. One was that it was ice, the other that it was rock. I tried to come up with a compromise where they were rocks coated in ice. This was when I was about six, and little was known about the place because no spacecraft had ever visited. It’s an example of my attempt to resolve an issue by finding a compromise between two opposing viewpoints. I’m not sure I would do that today, but my aversion to conflict often drives me in this direction. Another personal take on this is that it’s been so long since the Voyager probes discovered the detailed appearance of the rings that it’s hard to imagine things being any other way, but before they got there, the Pioneers’ cameras not being good enough to reveal that structure, everyone assumed they were smooth apart from the broad divisions we were familiar with and the Encke and Cassini divisions. It’s hard to remember what everyone used to think they were like. The question arises of whether there actually are smooth ring systems out there. Jupiter’s probably is, but it’s also quite insubstantial. Around another star system, or perhaps long ago in the history of this one, there may be or might have been extensive smoother rings, such as around the moonless Venus
This raises the question of how they got there in the first place. One relevant aspect here is that they seem to be temporary and in fact even the features which have been mentioned may be more transient than permanent fixtures. The rings themselves could be gone within a hundred million years, and since it’s fairly unlikely that we’d be around that close to their demise, the chances are they weren’t there soon after the planet formed, although another set of rings may well have been. The current set is probably less than 200 million years old, which is younger than the first dinosaurs and mammals. The chances are that the rings never formed part of a single larger object but are instead a collection of comets and asteroids which were captured by the gravity of the planet, although I don’t see how this makes sense because if they’re temporary it sounds much more like they were a single object which was broken apart. Asteroids are often rubble piles, so it does make sense that there was never a single object.
The whole subject of the rings is so involved and extensive that it’s almost like I’m talking about a different entity than the planet, but they’re also such an essential part of how we think of Saturn that it can’t really be mentioned without mentioning the rings themselves. Even so, we happen to be in a period of less than five percent of the Solar System’s age so far when Saturn has these rings. Maybe at another time Jupiter’s rings were much more obvious.
Moving on to the atmosphere, which in Saturn’s case is basically the whole planet, being so tenuous, the situation isn’t as simple as Jupiter’s because unlike the giant planet, Saturn is tilted. Whereas Jupiter is almost a model of simplicity, Saturn has an axial inclination of 27°, and since its years last almost thirty of ours it has seasons lasting more than seven years each. This leads to the same sort of “blowiness” as we get in spring and autumn, but on a far larger scale and a much longer period of time. Saturn’s cloud tops are also considerably colder than Jupiter’s, but like Jupiter it emits about 60% more heat than it absorbs. This is also less straightforward than the other planet because it can easily be accounted for there by it being so huge that it’s taken this long to cool down, but in Saturn’s case this is not so.
While I’m at it, this would probably be a good place to talk about the consequences of Saturn’s size and tilt. I’m personally guessing that shadows cast by the rings influence the weather. Twenty-seven degrees of inclination is slightly more pronounced than our own 23°.4 and all other things being equal the seasons will be somewhat more pronounced than ours, but also, the ring shadow reaches 48°from the equator, which creates a large colder area in darkness for long periods at a time, most pronounced during mid-summer and mid-winter. For the former situation there will be a particularly big temperature difference between the mid-latitudes under the Sun and those under the shadow. This would cause powerful winds into the area which would be weaker but still exist during the winter. It also has photochemical effects because the influence of ultraviolet light from the Sun is absent under the shadows. And it is “shadows” because of the various gaps such as the Cassini and Encke divisions.
Another markèd aspect of Saturn is, well, its aspect as the most “squashed” planet. It’s twelve thousand kilometres wider at the equator than the poles, giving it a gravitational pull almost 23% less there. Furthermore, since it takes only ten and a half hours to rotate on its axis, the centrifugal effect is quite large, though not so much as it on Jupiter. The average surface gravity at cloud top level is about the same as ours at sea level. Wind speed is as high as 1 800 kph, which is fifteen times hurricane force on the Beaufort Scale. Cloud top temperature is between -185 and -122°C.
Saturn has a rather blank appearance as a whole and is easily upstaged by its own rings, but it has some similarities to Jupiter in that it’s banded and has oval storms on its “surface”. The comedian Will Hay was also an astronomer and his chief claim to fame in that area is that he discovered one such storm, the Great White Spot, in 1933 CE. As an astronomer he made himself known as W T Hay in order to separate the two parts of his public life. He once said that if everyone was an astronomer there would be no more war because everyone would have life on this planet in perspective. On 3rd August 1933, he observed the spot on Saturn while Cynthia was quite bright and Saturn quite low in the sky, so conditions were far from ideal. Other astronomers were able to confirm its presence at about the same time. He made these sketches of the phenomenon:
His finding was published in the British Astronomical Circular on 4th August 1933. In a reference to the rise of Hitler, the ‘London Evening News’ published a cartoon of Hay standing on the rings and observing dark trouble spots on Earth, which actually chimes really well with his own attitude of getting perspective on human affairs by realising a sense of their relative scale. As a slight aside, I know I’m typing this with Russian manœuvres and Western posturing over the Ukraine, and it might look like I’m just ignoring it, but what I’m trying to do is provide the “Overview Effect”. When I make the observation, for example, that the Cassini Division is the width of North America but not even visible through a mediocre telescope from here, that’s meant to indicate how petty our squabbles are and the ultimate unity of this planet. If Hay’s drawing of his Great White Spot is proportionately accurate, it had a diameter about five times Earth’s, and this is important. Our own problems are of course major, but this makes the planet seem all the more precious because it’s a tiny oasis of life lost in the vastness of the Cosmos, even just of the Solar System. If the orbit of Neptune was scaled down to the circumference of Earth, Earth on that scale would be about the size of a double-decker bus or large tree, or perhaps a medium-sized back garden. That’s not insignificant but it’s still a lot smaller than the world, and that’s just the bit with the planets in it. I have seen a couple of Will Hay films by the way but didn’t get an enormously clear impression of what his cinematic work was like. I would expect it to be rather dated, and the same might be said about his astronomy but it still has the same effect.
Great White Spots are of course named after Jupiter’s Great Red Spot, but they’re harder to, well, spot from here because they aren’t red and Saturn is about twice as far away and somewhat smaller than the next planet in. Also known as Great White Ovals, they appear in the northern summer every twenty-eight and a half years. In 1876, Asaph Hall, who discovered the Martian moons, used one to time Saturn’s rotation period, although that assumes they don’t move relative to whatever counts as stationary for Saturn, which like Jupiter and the Sun is hard to define. Oddly, none were seen before that one even though telescopes had been good enough for a very long time, and it’s thought that before that, Saturn was undergoing a quiescent period similar to the one which has sometimes made the Great Red Spot (GRS) disappear, so there would’ve been some before the telescopic era but nobody would’ve been able to see them. They also appear alternately in the northern temperate zone (NTZ) and at the equator. This makes them similar to the GRS in that they occur in one hemisphere but not the other, in this case the opposite one. They differ in that they leave long trails and have lightning. They also don’t have “eyes”, unlike Earth’s hurricanes, but are active all the way to the centres. It appears that Saturn’s atmosphere is more humid than Jupiter’s and when it cools, rain or snow takes heat away from it, being proportionately much heavier than the air, which is mainly hydrogen and helium, than Earth’s nitrogen-oxygen atmosphere. This cooling effect means there are weaker air currents in the upper atmosphere, which results in a colder and very stable condition only disturbed in the summer when the Sun heats it up again and gives rise to storms. An individual storm can be larger than Earth, as was Will Hay’s for example.
Like Jupiter, Saturn is divided into zones and belts, like this:
The polar regions are of special interest and I’ll be returning to them, but for now the northern region is much bigger than the southern, reaching down to 55° whereas the Southern Polar Region reaches down to only 70°. The brightest part of the planet is the Equatorial Zone, bisected by the narrow Equatorial Belt, which could be constantly in receipt of D Ring fragments. It’s the EZ which has the ovals along with the NTZ. Many of these are hard to see from here due to being covered by the rings much of the time, although they’re so thin that everything is visible when the planet is edge-on to us.
The whole planet is rather bland-looking and therefore differences in the clouds are harder to see, if there are many. Features over a thousand kilometres across are only about a tenth as common as they are on Jupiter. All the way through this bit, I feel like I have to compare to Jupiter and that seems quite unfair. Why can’t Saturn just be considered in its own right? Nonetheless it is also the planet most like Jupiter. There is not much helium at six percent. This is thought to be because by about two æons ago, the planet had cooled enough for helium to rain out of its lower atmosphere onto the core. This was very deep down and under enormous pressure. It doesn’t mean the planet cooled down to the extreme low temperatures required for helium to become liquid at sea level pressure on Earth. Helium, incidentally, wouldn’t behave like it does in our atmosphere. Because Saturn has such a low density, and also so much hydrogen in its atmosphere, helium is twice as dense as its air and would tend to sink. This process took the heat from the then warmer upper atmosphere into the depths, which is thought to be why the centre of the planet is hotter than might otherwise be expected.
The internal heat is a factor in driving the weather systems. On Earth, most of the heat comes from the Sun although some is trapped by greenhouse gases and volcanoes would sometimes make a very minor contribution. On Saturn, most of it comes from below, and given that it’s further from the Sun than Jupiter, proportionately more than on that planet. Most heat is lost from the poles and the least from the equator, meaning that the poles can be the warmest parts of the planet. I’d expect the oblateness to contribute to this as at the poles there are twelve thousand fewer kilometres for the heat to make its way through than at the equator, meaning that the atmosphere forms an uneven insulating blanket wrapped around the interior.
There are the usual problems of defining the surface of a gaseous body. In this case it’s fairly clear, because the cloud tops are also the point at which the temperature reaches a minimum at around -183°C and is higher both above and below it. This does, however, mean that the troposphere, i.e. the layer of atmosphere immediately above Earth’s surface, is actually below the surface on Saturn. The top layer of clouds is one of several, the top being ammonia, beneath which is ammonium hydrosulphide. This is one of the chemicals used in “stink bombs”, so the planet might look beautiful but it actually smells revolting. Its boiling point is 56.6°C, so there is adequate range for the existence of these clouds in aerosol form. Below them are water vapour clouds like we have here. These are getting on for two hundred and fifty kilometres down, where the pressure is about ten times that at sea level on Earth. Saturn’s clouds tend to be similar colours and are thicker than Jupiter’s, with fewer gaps, all of which contribute to the planet’s uniform appearance from space.
Because Saturn is the least dense planet, and in connection with that has lower surface gravity, the pressure increases more slowly with depth. The atmosphere is both less dense and lighter. Coincidentally, it’s also lighter in the sense of not being as dark, although in another sense there’s only a quarter of the sunlight present at Jupiter’s orbit, but it does reflect more sunlight.
Saturn has a diameter of 116 460 kilometres, which is nine and a half times ours. This makes it something like seven hundred times Earth’s volume although the oblateness makes this complicated to calculate. However, its density only being 68.7% that of water, a “Saturn” the size of Earth would have lower gravity than Cynthia’s at the surface. It also wouldn’t hold together very long for that reason. It also gives it eighty times our surface area, which means that Earth is to it roughly as Australia is to Earth. Hence Earth is actually a somewhat respectable size compared to the planet, being equivalent to a small continent, although that does also include all the ocean. In terms of land, Earth is analogous to the Sudan on this scale. As far as Jupiter is concerned, it’s feasible to be more exact due to the oblateness of both planets. It’s 83% of its diameter and has 69% of its surface area and 57% of its volume. However, its mass is considerably smaller at only 29%, which illustrates a tendency found among exoplanets that on the whole they don’t get much larger than Jupiter because beyond that mass the interior just gets increasingly compressed. While I’m at it, there is also a big gap between the largest planets and smallest stars which remains unexplained, and there are also “puffy planets” and large planets which are in the process of forming and contracting.
A layer of haze above the clouds might be hiding some of the cloud activity further down. The temperature also contributes to the light appearance as many of the clouds are made of frozen white or pale yellow crystals. There are a number of jet streams. The equatorial one has a velocity of 1 800 kph, which is two-thirds of the speed of sound in that region but supersonic for our atmosphere. Then there are three easterly jets in each hemisphere with latitudes of forty, fifty-eight and seventy degrees. All of these are quite stable and durable. However, unlike Jupiter the winds don’t correspond to the stripes. Surprisingly, the winds are symmetrical with respect to the equator, which they “shouldn’t” be because the planet is tilted and has seasons which are in some ways more distinct than even ours. This suggests that the winds extend deep into the planet and that it rotates as a series of nested cylinders, because the heat from the Sun doesn’t seem to be the main influence on the winds. If it were, there would be more seasonal variation. This also means that some of the cylinders actually reach the core, and these are more likely to be different in the different hemispheres, meaning that the polar regions further than 65° from the equator are likely to differ more than the temperate and equatorial ones.
If the visual contrast is ignored, there are many similar structures in Saturn’s and Jupiter’s atmospheres. The jet streams in both are thought to be powered by eddies. However, on Saturn they’re four times stronger, can be twice to four times the width and don’t relate to the banded cloud structure.
Saturn’s hexagon in false colour
No account of Saturn’s atmosphere would be complete without a reference to the Hexagon. Jupiter has its Great Red Spot, Saturn its Hexagon. This is a hexagon (really?) in the north polar region whose sides are 14 500 kilometres wide. It was first detected by Voyager 1 when it passed over the north pole. However, it took another six or seven years before anyone noticed it because there was so much information available. It was initially thought to be the result of a storm happening on the edge of the northern polar region but when Cassini visited more than twenty years later, but less than an entire orbit of Saturn later, it was still there, tough at that point the north pole was in darkness so it was imaged in infrared. It has now been seen from Earth. Also puzzling is the complete absence of a similar shape at the south pole. Jupiter doesn’t have a hexagon, but it does have a polar vortex surrounded by eight other equidistant storms. Other planets with atmospheres also have them, including Venus, Earth and Mars. Mathematical models were able to produce triangles but not hexagons. After some time, it was suggested that the shape emerges from a wave passing around the northern polar circle of the planet of a certain length which interacts with itself to produce a kind of interference pattern. It rotates once every Saturnian day of ten and a half hours. What we see is quite like active noise cancellation, where a wave of reverse phase (troughs and peaks in opposite places) is used to reduce sound level.
Another aspect of the Hexagon is that it has certain things in common with the former Antarctic ozone hole. Both are atmospheric regions sealed by a rotary jet stream, whose atmospheric composition differs markèdly from their surroundings. Over Antarctica, the jet stream prevents ozone from entering from outside and concentrates CFCs inside, then the winter conditions exacerbate it. On Saturn, large droplets cannot pass into the polar region, again due to the jet stream, and again winter conditions strengthen this effect. Also, the Antarctic ozone hole was worse than the situation in the Arctic, so both structures exist over only one pole.
The central vortex is about four dozen times the size of a typical hurricane eye on Earth. The colour of the Hexagon changes – it can be blue or red. Presumably the blue is due to the same effect which makes the cloudless sky blue here and is connected to the size of the aerosol droplets, which are smaller inside the shape. It spins counterclockwise, though quite slowly compared to the rotation of the planet as a whole, insofar as it even does rotate in one piece, but some of the vortices within it spin clockwise. To the human eye, the area would look like this:
The central hurricane, PIA14947, unlike the Hexagon, does have its counterpart at the south pole. It’s a little under two thousand kilometres in diameter, and takes only six hours to rotate, so unlike Earth, whose poles are stationary and polar regions rotate slowly on account of it being a solid object, Saturn’s poles rotate faster in terms of revolutions per minute than the rest of the planet, and the inner ring moves even faster, at the same speed as sound on Earth at sea level although it doesn’t break the sound barrier for that part of Saturn.
The south polar vortex is eight thousand kilometres across. Although I’ve heard that “conditions” mean there is no hexagon there, that doesn’t really explain it to me and I haven’t managed to find out why there’s this asymmetry. With Earth, the Arctic and Antarctic regions are very different due to the presence of an ocean at the North Pole and a continent at the South, but this doesn’t apply to Saturn. Nor does it have anything to do with spacecraft visiting it at particular seasons, as Cassini was there for quite some time and the Voyager probes flew by during different seasons compared to Cassini. The south pole is 60°C hotter than the equator, which has been likened to discovering Antarctica is hotter than the Sahara, and given that Saturn as a whole is so much colder at cloud level, the contrast is even more dramatic. Clouds around the area are thirty to six dozen kilometres higher than their environs. This is known as an “eyewall” and has only otherwise been seen in hurricanes on Earth.
I haven’t mentioned the interior of the planet in detail yet. The scale of the interior is somewhat different than Jupiter’s due to the fact that Saturn is smaller, has much weaker gravity and is less dense. Both planets’ magnetic fields are generated by liquid metallic hydrogen near the centre, but in Saturn’s case the amount is proportionately smaller at forty-six percent of its diameter as opposed to Jupiter’s seventy percent. The interior of Saturn has relatively little helium compared to Jupiter’s. The rocky core is about the size of our own planet, but also has three times our mass. These differences relate to those between the weathers of Jupiter and Saturn. The magnetic field is around a thousand times stronger than Earth’s. Like Jupiter, the “true” rotation of the planet can be found by monitoring its radio waves, which have a period of ten hours, thirty-nine minutes and twenty-four seconds, the peak in strength being defined as local noon. The centre of the magnetic field is 2 400 kilometres north of the centre of the planet itself, but it’s also the only planet whose magnetic field is almost perfectly aligned with the axis of rotation. A compass on Saturn would actually point to geographic north.
That, then, is it for Saturn. I was rather surprised how long this one took me although I did also write about twenty thousand words of fiction while also writing this. Even so, Saturn is quite an involved planet, mainly because the rings are so prominent and important but also because I didn’t want to neglect the planet itself, which is as interesting in its own right. And you might think that now I’ve got to Saturn, I’m half way through my coverage of the Solar System. Not a bit of it! Saturn has so many moons that this is still the first half of my “trip”, as do Uranus and Neptune, although Saturn’s moons are much better known, and although Jupiter has four large moons and Saturn just ones, some of its smaller moons are large enough to be thought of worlds in their own right and this skews the half way point way down the line.
No, King John did not sign the Magna Carta here. Buddy Holly is not alive and well here. Christmas has never been celebrated here. Nor is this in Surrey. That’s Runnymede. Incidentally, Buddy Holly doesn’t live there either, although Christmas has definitely been celebrated in it. However, this is Ganymede, the largest moon in the Solar System and therefore the largest Galilean. It’s larger than Mercury and Pluto, but smaller than Mars. That said, it’s only 45% of Mercury’s mass.
To explain the rest, ‘1066 And All That’ claims that King John signed the Magna Carta on Ganymede. This opens up the possibility of a weirdly transposed version of English or British history where all the stuff that went on in our Middle Ages could be copied and used to tell the tale of a British version of the entire Solar System, perhaps with Jupiter as its capital. That makes me wonder where Scotland is. Ganymede also turns up in the rather startlingly entitled ‘Buddy Holly Is Alive And Well On Ganymede’, a novel which recounts the tale of one Oliver Vale, conceived at the moment of Buddy Holly’s death, who thirty years later finds that all the TV stations in the world have their signal hijacked by a broadcast of a rather bemused Buddy Holly on Ganymede who knows nothing of his situation except that there’s a TV camera pointing at him and a sign next to it reading
For assistance, contact Oliver Vale, 10146 Southwest 163rd Street, Topeka, Kansas, U.S.A.
It’s actually quite a good book.
As for Xmas, Isaac Asimov wrote a 1940 CE story called ‘Christmas On Ganymede’ about a mining company on said moon whose employees hear about Christmas and proceed to go on strike until visited by Santa in his flying sleigh pulled by reindeer. This version of Ganymede is much denser than the real one and has an almost-breathable atmosphere containing oxygen. I suspect Asimov already knew Ganymede wasn’t like that.
I’ve always called it “Ganymeed”, but it’s supposed to be pronounced “Ganymeedee”, which is how Buddy Holly says it in the book so it must be true, but I think both are acceptable pronunciations. Ganymede, or Ganymedes, himself, was a Trojan prince abducted by Zeus to serve as a cup-bearer to the Olympians. This means Ganymede was Zeus’s sexual partner in a pederastic setting, so the situation is mixed. On the one hand, we have a moon acknowledging homosexuality, but on the other current values place him as a victim in the same way as Io and Europa are of Zeus’s insatiable lust. He’s the basis of Aquarius, but the constellation Crater has nothing to do with either. I don’t know why Ganymede was the name given to the largest moon and I’m now wondering if Kepler or Marius, who named them in 1614, was secretly gay.
The next largest moon is Saturn’s Titan, which is also larger than Mercury. This makes it the ninth largest known object in the system. It’s the tenth largest by mass, again just ahead of Titan and giving it a larger surface area than Eurasia by quite a margin, and slightly larger than the Atlantic. It also contains an internal ocean with more water than exists on Earth. It takes four times as long to orbit Jupiter as Io does, and twice as long as Europa, so once again it’s in orbital harmony with other Galileans. It’s also the most massive moon, which puts it in a slightly odd position as its surface gravity is lower than Io’s or Europa’s, because it continues the trend of decreasing density with distance from Jupiter. It gets closest to Europa, at 400 000 kilometres, just over the distance between Earth and Cynthia. Callisto is somewhat apart from the others. Io and Europa taken together are less massive, but the imbalance between a single large moon and several or many smaller ones whose combined mass is less doesn’t apply in the Jovian system. In a way, Ganymede is the Jupiter of Jovian moons. It also, perhaps surprisingly, has the lowest escape velocity of all the Galileans, meaning that it won’t be able to hold onto anything like a proper atmosphere, or even the kind of atmosphere the inner two have. Like those though, it orbits within the radiation belts. Until the outer planets and moons were more thoroughly explored in the 1980s and more recently, it wasn’t clear out of the three moons of Ganymede, Titan and Triton which one was the biggest.
The moon was big enough for large Earth-bound telescopes to make out at least one of its surface features, Galileo Regio. The rather vaguely named regiones are Galileo, Marius, Perrine, Barnard and Nicholson, and are the dark patches. They also have sulci across them, of which there are over a dozen. Unlike the two inner Galileans, Ganymede’s surface has not been extensively reworked due to tidal forces and it therefore has a fair number of craters, though not as many as somewhere like Mercury. It’s the brightest of all the moons in our sky other than Cynthia, although it’s dimmer per unit area than Europa, because it’s also the largest. To some extent it resembles Cynthia, as the darker regiones are like the maria (seas) and there are also craters, but the broad sulci are not found on the lunar surface. Due to the surface being largely ice and at this temperature being softer than rock as we know it, it isn’t as craggy either, although it’s not as smooth as Europa. The gravity being lower might contribute to this. The maximum elevation is found among the sulci, which reach about seven hundred metres above the surface.
Galileo Regio is the size of Antarctica. It covers a third of the hemisphere facing away from Jupiter. Putting this into perspective, this means that as far as Earth is concerned, our continents and oceans would mainly be visible from Jupiter with a good telescope, although Australia might not be, and Jupiter is almost our neighbour in cosmic terms. All we’d be able to do from that distance is discern that the continents and oceans existed and were differently-coloured from each other. The most distinctive feature of the moon, and let’s once again affirm that by a more recent view than the 2006 IAU definition Ganymede is also a planet as much as Pluto is, is its grooved surface and the stripe-like features where they’re bundled together. These lighter sulci are newer than the dark regiones. It and Earth are the only known bodies which have lateral faulting, that is, where a fracture in the ground leads to the surfaces sliding along the fault rather than subsiding or rising. These sulci divide the terrain into polygonal blocks, the regiones, up to a thousand kilometres across. Although the moon is not currently active and drifting doesn’t occur, it has done in the past and this arrangement of plates separated by lateral fault zones is similar to Earth’s continental plates, making Ganymede the only other world in the system which has this kind of arrangement. Not even Venus, which is geologically quite like Earth in many ways, has this feature.
The crust is somewhat weak and can’t stand heavy weights upon it, and is underlaid by a much deeper layer of water. This leads to “drowned” looking craters which look quite similar to the ones on the lunar surface which became flooded with lava in æons past, but unlike them their origins are not associated with flows of liquid but mere collapse into the surface due to the weakness of the material. Most craters are on the regiones because they’re older. About half of the bulk of the planet (let’s call a spade a spade now we’re allowed to again) is ice and half is rock, although it isn’t clear how this is distributed. It does have a very large rocky core under the deep oceans, and also its own magnetic field, practically guaranteeing an iron-rich centre like Earth’s. Although one way of looking at the interior is as a frozen-over deep ocean of salt water over an ocean bed, it could equally well be described as a planet where ice and water replace our rocks and magma, with a mantle of water rather than molten rock. However, because the gravity is so low there, the pressure at the bottom of the ocean/mantle wouldn’t be excessive. As well as ice, there is clay mixed in with the crust, and there may also be ammonia ice. There’s also more dry ice at the poles, and as with several of the other moons the leading and trailing hemispheres of the planet have different surface compositions, probably because of Io again as the trailing side has more frozen sulphur dioxide. I have to admit that I don’t understand why these moons have deposits from Io on the trailing hemisphere rather than the leading one because it seems to me that they’d be entering a cloud of the stuff, which would then land on the “front” of the moon.
The crust is eight hundred kilometres deep and contains the kind of ice we’re familiar with here along with, as I’ve said, clay, but may also contain bubbles of the same kind of oxygen as we have in our atmosphere. Above it is, for the same reasons as on Europa, an extremely thin atmosphere of oxygen and ozone, and I’m guessing the ozone is formed by Jovian radiation in the same way as an electrical spark forms ozone here. This is a small fraction of a nanobar in pressure. Deep in the crust are large clusters of rock, which might either be piles at the bottom due to its inability to support their weight or embedded in the crust due to its ability to support it! There is then what may be a further hundred kilometres of water, ten times deeper than our Marianas Trench. This is salty, as can be seen by the way aurora behaves on the planet, influenced by the magnetic behaviour of the brine. The fact that there is so much water seems appropriate for a planet named after Zeus’s water-carrier. Ganymede is the only moon in the system with a magnetic field.
Beneath the ocean lies a layer which makes the existence of life as we know it unlikely. Although the lower gravity reduces the pressure, the ocean is so deep that it manages to compress the water back into ice, but of a different kind than we would come across here: tetragonal ice. There is more than one kind of tetragonal ice, and this one is referred to as “ice VI”. The ice we encounter close at hand on Earth’s surface is hexagonal, as can be seen for example in hexagonally-symmetrical snowflakes and the hexagonal columns which form in frost and elsewhere. Ganymede’s lower layer of ice is heavier than water and more akin to the normal behaviour of freezing materials than our ice, because it contracts on freezing. Its crystals consist of elongated cuboids composed each of ten water molecules. Depending on the pressure, its melting point can be as high as 82°C or as low as 0.16°C and it’s 31% denser than water. This kind of ice turns up in the interior of some icy moons. In Ganymede’s case it seems to rule out the existence of thermal vents which could provide energy for life, as it probably does elsewhere in the Universe in many ocean planets, because it forms a thick layer on top of the rocky surface below it which volcanism wouldn’t be able to penetrate.
The structure of the ocean may not be that simple though. The ocean may in fact be arranged in four layers separated by shells of ice of different kinds. Beneath the “ordinary” ice crust on the outside, there may be a relatively shallow ocean on top of a layer of ice III snow. Ice III has a similar crystal structure to ice IV, but because this is snow it would consist of non-hexagonal flakes, perhaps more like needles than hexagons or six-pointed stars. This could be floating on top of a second, deeper ocean, below which is a layer of ice V. This is tens to hundreds of kilometres deep and is monoclinic in structure – that is, two of its axes of symmetry are at 90° but the third is slanted. Examples of monoclinic minerals include gypsum (blackboard chalk), jade and some feldspars (which can be enormous crystals the size of buses found in caves). Then there’s a final layer of water followed by the aforementioned ice VI base.
Below the rocks is a liquid outer core consisting of a mixture of iron pyrites (fools’ gold – this is a sulphide of iron) and iron, and the final solid inner core is made of iron.
A few other bits and pieces. The radiation on the surface is sufficiently weak to be fatal to unprotected humans after a few weeks, but it still wouldn’t be a good idea to go there. There are ray craters like those we see on Cynthia, such as Tycho, which may have light or dark rays depending on where the impact occurred. The “drowned” craters are described as “palimpsests”, after the faint remnants of writing seen in old documents which have been over-written later. Nobody understands why there is a strong magnetic field.
For such a large moon I find it a little disappointing that Ganymede isn’t better known. It feels like there’s either a lack of information on the place or that it’s overshadowed by its more exciting neighbours. Io has the hyperactive volcanism, Europa the possibility of life. Ganymede has if anything a greater right to be thought of as a planet than any other moon in this solar system, being larger than Mercury, and might be expected to be either more interesting or a better-studied place but it definitely comes across as more placid. Also, for its size it’s surprisingly light. This lack of knowledge is likely to change in the next few years when the European Jupiter Icy Moons Explorer (JUICE) is launched to investigate Europa, Ganymede and Callisto, excluding the non-icy Io. This will ultimately orbit Ganymede for around two years before being crashed into its surface. There’s a lot of that, isn’t there?
A few years ago on this blog, I went through every episode in the Original Series of Star Trek and reviewed them all. Well, I say that. One of the posts was actually a short story told from Uhura’s point of view as she sat around on the bridge with decidedly relaxed hair not doing much while the rest of the bridge crew beamed down to the planet, but leaving that aside I did review every episode, and I also did the animated series and TNG as a whole. If you’re interested, the reviews start here.
Now it’s occurred to me that I have now written a few posts on the subject of various bodies in this Solar System, not very systematically and partly because a Generative Adversarial Network (GAN) suggested them to me. I am going to ramble just a little bit in this post, so I’ll go off on a tangent here and talk about what a GAN is.
A GAN is a pair of neural networks used in Artificial Intelligence (AI) which competes against itself to produce better results. What’s a neural network then? Well, to some extent we are, although not entirely, and there’s some controversy as to how much a human being’s essence could be captured using such a structure. Most of the time, the term “neural network” doesn’t refer to a biological entity like a human being or a nematode worm, but to a simulated structure being run in software which attempts to mimic the function of a real such network. It has an input layer consisting of sensors, for example, one or more hidden layers, where the signals from the sensors are combined and acted upon, and an output layer, often in the form of a visual, textual or auditory representation. The retina is an example of a neural network, and starts to process the visual input to the eye before presenting it to the brain. For instance, rod cells are more sensitive than cone cells and several of their inputs are combined by a neuron-based inclusive-or gate such that a single stimulated cell will set off the neuron, enabling one to see better in low light, whereas the cone cells are in one to one correspondents to the neurons, enabling higher resolution vision in colour in good light conditions. Individual nodes in an artificial neural network can be made more or less sensitive according to their “experiences”, so they can be gradually trained. This technique is used in a GAN. These pit two neural networks against each other. An individual network can learn, for example, to recognise a face by being shown thousands of pictures of faces and producing ratings as to how face-like it judges the input to be, which is then judged by the human programmer, allowing it gradually to get better at recognising them. This human programmer can be removed and replaced by a software training judge, which allows the process to occur much more quickly. GANs focus on the weaknesses. For instance, they might be good at recognising pairs of eyes but not mouths, so if the eye recognition is good enough, the other part of the program will concentrate on making it better at knowing what a mouth looks like. I haven’t described this particularly well, but GANs are basically artificial intelligence which is able to recognise and predict, and even make, particularly good patterns. Faces for example:
GANs and other AI can be really dodgy because if you train them on the wrong source material they can end up freezing previously human prejudices into the software. For instance, a GAN trained on job applications may start reproducing the sexism and racism of the recruiters and a GAN trained on mainly White human faces and those of other primates has ended up classifying Black faces as those of gorillas. It’s therefore both far from perfect and potentially insidiously harmful, because nobody knows exactly how they function.
I have referred previously to my use of GANs on here to work out what this blog is actually about. In case you don’t already know, it’s called ‘A Box Of Chocolates’ because you never know what you’re going to get, and nor do I. In fact, it’s possible that an outsider would be better at recognising what a typical Nineteenthly post would be about and look like than I would, because I’m not aware of my prejudices and style, but other people probably are. I do have some self-awareness but I don’t know how much, which raises the question of how well we can really know ourselves.
All of that notwithstanding, I do sometimes use GANs to inspire blog posts. It would make a lot of sense to do this with popular titles written by others, but I suspect this would have two adverse effects. It would restrict subject matter to the more “commercial” and popular subjects,and it would make them clickbaity, which is very irritating. We already get exposed to too much stuff which is inside our reality tunnels and I don’t want to make this any worse. On the other hand, I know I’m unconsciously eccentric and therefore the things I go on about and the ways I react are unusual. For instance, I once surprised someone in a discussion about the legalisation of hard drugs by saying that a single parent in a deprived area might fear the effect of the decriminalisation of hard drugs on her children because it might stop her from selling them and supporting her family. This is apparently an unusual juxtaposition of ideas. However, the kind of ideas I have might still be detectable by a GAN.
In a remarkable turn of events, I began the next paragraph with a cliché (maybe not so remarkable after all), so I am subject to talking about “normal” stuff from time to time. Even so, I do use this technique and it’s almost a form of divination, like looking at tea leaves or dropping molten lead into water and interpreting the shapes, because the text results often read as if they’re referring to events and preoccupations in my life which clearly the machine can know nothing about. Or can it? There’s a famous case of a teenager who got mailed vouchers for baby stuff because the AI interpreting her shopping habits, which were not obviously anything to do with being pregnant, was able to predict that she was going to have a baby soon. She hadn’t told her parents, so this is how they found out. It’s conceivable (geddit?) that someone might not know they’re pregnant before the computers do, and likewise software might be able to deduce facts about oneself which one is perhaps repressing or doesn’t even know. This is often useful, as with the CASCAID career software, which has for at least forty years been suggesting careers to schoolchildren and others. At the same time, we see patterns which aren’t really there, and with the psychotherapist program ELISA for example, it really feels like one is talking to a counsellor and it can even be useful.
In a remarkable turn of events, as mentioned here I submitted some recent blog titles and was rather surprised to find that rather than suggesting more possible subjects, the GAN began to type out what looked very much like a blog post about Titan, hence my actual production of the last post. Most of the AI-generated text didn’t make much sense. For instance, it mentioned a crater being in orbit above the moon. However, some of it really did, and the general topic of the text was the possibility of humans settling on Titan and exploiting it for economic benefit, which I ended up mentioning in the real post.
Another possible use for the GAN, apart from actually getting it to write articles which would at the moment mainly be gibberish – they would appear to make sense and use grammatical sentences with English words in them, but the whole post would be nonsense – is to submit tags which are popular in order for it to generate more. I’ve also done this and it works quite well. Incidentally, if you put in this paragraph, this is one result:
ussion/comments/29d2w3/why_are_there_exceptions_to_the_guests_and_ancillary_suggestion_to_add/ You can read that at the end, too. The idea here: a link to another subreddit which mentions the use of "GAN" - is just a joke.
The article at the top is a bit hard - it includes this tag, but no one has heard of it. It seems that many people actually prefer to keep it unimportant. Here it is, in the final form of this post:
For a comment on this post here is a screenshot of what we have just submitted: http://redd.it/29d2w7/reddit_posts/3
For an argument with the question here is about the link to this reddit, which is not worth mentioning.
I used the following for this
Not very useful!
After that digression then, here is my immediate plan. I’ve found myself covering various planets, moons and other bodies on this blog, but one thing I’ve never done is a systematic survey of the individual aspects of the entire Solar System. I’ve mentioned Mercury, Venus, Mars, Titan, Uranus, Neptune and Pluto but none of the moons or asteroids, or the general layout of the system, which is quite germane. However, if I did this incessantly like I did with ‘Star Trek’, the reader would be subjected to day after day of posts on various worlds, so although this forms part of my plan I also want to intersperse it with other topics. Otherwise, you will “know what you’re gonna get” – yet another post on a planet. It also means you can skip it if you find it boring.
Now is also a good time to say something about my attitude to astronomy.
It’s really easy with astronomy to slip into a mindset that it’s something that’s just “out there” with no connection to everyday life. This is a problem I used to have with the science workshops when I was more directly involved in home education. In general, physics, chemistry and biology lend themselves really easily to activities and learning for a group of children who turn up during the day. However, children also have bedtimes and in this country it doesn’t get completely dark in the middle of the summer, so for astronomy there isn’t much “hands on” activity for groups. The Sun and Cynthia (“the Moon”) are available and you might get lucky and witness a transit of Venus, but beyond that there’s precious little. Hence if you’re not careful you end up dealing with astronomy at arm’s length, as it were. It isn’t helped by the fact that a lot of space stuff is associated with planetary romance, space opera and science fiction, which further removes you from the real subject matter. It introduces all sorts of preconceptions about space, such as the idea that the asteroid belt is a hazardous zone strewn with dangerous spinning rocks or that space is like a two-dimensional ocean. There’s a place for all that of course, but I want to really feel space in all its gritty reality. One of the Apollo astronauts was asked about what colour the lunar surface was, and he replied that if he wanted to see something which was the same colour he’d go out and look at his concrete driveway. There’s something really mundane about this, and whereas it makes it sound boring it also provides a real link between everyday experience and astronomy which can be hard to come by.
This, then, is my plan. I will be blogging about various worlds in our Solar System and about the Solar System as a whole, interspersed with posts on other subjects, and I aim to do it in such a way that it won’t seem to be abstract or “out there” but as real as going down the street to the chemist. We all know in the abstract that we’re in space and live on a small blue dot lost in the vastness of the Cosmos, but we also spend a lot of time thinking of ourselves as like the filling in a sandwich with a black colander on top of it. There are good practical reasons for not thinking of the world like this, such as the constant awareness of the limited nature of Earth’s resources, the unity of the planet and the preciousness of this tiny oasis. It also seems in order to be aware that the other worlds around us are also whole worlds, as much as Earth is, and recognise what might be special about our Solar System compared to others, and what’s typical.
At some point maybe about forty years ago it was noted that there were thirty-three moons in the Solar System plus nine planets, and in addition to those there are the centaurs, asteroids, smaller moons, comets and Kuiper Belt objects. Nowadays many more moons are known than that number in either the Jovian or Saturnian systems alone. Hence there is ample material for this kind of thing, and also ample material to be boring with. One thing I want to emphasise is that because so far as we know this is the only world with life on it, I want to approach the celestial bodies on their own terms, not just as potential places for humans to settle on or where life might or might not exist. The Universe is not just about life. That said, I will also be considering this aspect, along with what humans have had to do with them because otherwise there’s a risk of making it too disconnected with what we know.
On a personal note, I’m somewhat impaired due to the fact that I live in a cloudy part of this planet, have poor eyesight and am not blessed with dark skies, although this may change. People with good vision may not appreciate the problem with looking at the night sky when you’re short-sighted. Stars, with the Sun’s exception, are of course very dim compared to what we generally see during the day. I have the choice of looking at the sky with glasses or without. With the latter, the light of a given star is very blurred and diffuse, to the extent that I don’t think I can even see second magnitude stars such as Algol or Polaris. With the former, the material from which the lenses are made cuts out much of the light before it even reaches my cornea. Therefore my only option is to use a telescope or binoculars. I used to share a reflector with my brother, but unfortunately lost some vital bits of it in the back of someone else’s car, so that was that really. All of this leads to exactly the kind of disconnection I want to avoid with the rest of the Universe. I think this may have led to me over-compensating for my disability, to surreptitiously quote Mr Adams for the second time in three paragraphs, and I feel a more urgent pressure perhaps than most to make this connection.
Quick summary then. Our Solar System currently probably extends at least a light year and a half in each direction from the Sun. Beyond that point, the gravitational pulls of other stars become significant and an object can’t be said to be orbiting it. As the Sun moves through the Galaxy in its orbit, which lasts 200-odd million years and has a circumference of around 160 000 light years, it and other stars around it approach and recede from each other in their courses, and because of this the Solar System doesn’t have a fixed size, and it isn’t spherical either because stars of different masses are at different distances in different directions. I’ve chosen to define the Solar System here as the Sun plus the matter which is more influenced by the Sun’s gravity than other stars or similarly massive bodies. This is more or less how other people, including professional astronomers, define the Solar System, but it has a few anomalies. For instance, if a massive black hole entered what we think of as our Solar System, the regions where its gravity won over the Sun’s would not then technically be part of the Solar System, and when ʻOumuamua entered our Solar System recently it would have become part of our Solar System despite its origins elsewhere. There is a plasma-related “heliopause” which also constitutes a kind of barrier between us and interstellar space, constituting a fairly useful border. This is where the charged particles being shed by the Sun, also known as the “Solar Wind”, reach the point that their energy is no longer greater than that of the same kind of particles moving between the stars. The region inside this is known as the heliosphere, although it isn’t spherical because it’s like a bow wave and wake generated by a ship sailing through the sea, and there’s a long tail behind us in the opposite direction to the Sun’s movement through the Milky Way. There are currently two spacecraft outside the heliopause, the Voyager probes, but these have only managed to leave because they are moving in the same direction as the Sun and therefore have encountered the “shock” at almost its thinnest point. These will be joined at some point by Pioneers 10 and 11 and the New Horizons craft which was sent past Pluto.
This narrower part of the heliosphere is about a hundred times the distance of Earth from the Sun, or a hundred astronomical units or AU. Within it is the “termination shock” and between the two is the “heliosheath”. The reason this is seen as the border with interstellar space is that it’s where matter originating from the Sun stops moving outwards and is dominated by matter from elsewhere, i.e. interstellar space. However, there is a large cloud of objects far outside this called the Oort Cloud, which is a kind of reservoir of comets. This is vast. The planets we know of orbit within a region less than a thousandth of the size of the Oort cloud in each direction. As stars move through the neighbourhood of the Sun, their gravity slightly perturbs these objects and sometimes causes them to plummet inwards towards the planets, at which point they start to vaporise and become comets. Comets can move in three different ways. One is as usually very elongated ellipses. The closest comet of this kind has been Encke’s Comet, which took only three and a bit years to orbit the Sun and was therefore mainly inside the asteroid belt. This led to it losing most of its icy mass to space due to being constantly heated. When this happens, a comet becomes a cloud of meteoroids, and the well-known meteor showers which occasionally afflict our planet known as the whatever-ids, such as the Quadrantids or Leonids, are named after the constellation from where they appear to radiate as Earth moves through them. In the case of the Quadrantids, the constellation concerned is no longer used but the name of the shower is a monument to it. A comet can also move parabolically or hyperbolically. If it does either of these things, it will head out of the Solar System never to return, and it may in fact be from another Solar System entirely. Some comets have orbital periods so long that they haven’t been in the inner Solar System since the extinction of the non-avian dinosaurs, and in those cases it can be very difficult to determine whether they are in fact permanent residents of the system or not. Over the period of time the longest comets orbit, Earth and the Sun will have moved from the opposite side of the Galaxy, half way round their orbit.
It’s been suggested that objects in the Oort Cloud could be used to set up bases acting as stepping stones to other star systems. Although they’re thousands of millions of miles apart from each other, they form a fairly even distribution and the distances between them are minute compared to the distances to the nearest stars. Unlike the more visible parts of the system, the gravity of the Sun is not strong enough to force them to orbit in a flat arrangement like the planets do, so this could be done in any direction. This also means that comets can arrive from any direction into our part of the system. It’s possible that if we ever settled on outer Oort Cloud objects, we would technically enter another star system in a seemingly quite trivial way, from hopping between two distant members of the Sun’s and the Centauri system’s clouds, or even just by having an object move away from the Sun sufficiently to be technically more attracted by the Centauri system. The thing about the Centauri system, which is α Centauri A and B, Proxima Centauri and associated objects, is that its combined mass is more than twice that of the Sun, so it will pull on distant objects more forcefully than the Sun well before they get halfway there. In another direction is the Sirius system, which is even more massive, since one star is 2½ times the Sun’s mass and the other about equal to the Sun’s. Since it’s 8.7 light years away, this puts the limit of the Solar System in that direction at less than two light years even though Sirius is more than twice the distance of Centauri. In the recent past, i.e. the past few million years, stars have moved through the Cloud with their own clouds, causing comets to move in and sometimes hit the planets, including of course our own on numerous occasions, notably in the Gulf of Mexico 66 million years ago.
The inner Oort Cloud, alias the Hill Cloud is less perturbed by other stars and more flattened, and is the source of the comets which orbit near the plane of the planets. The reason for believing in the presence of these clouds is that comets have a limited lifetime once they enter the inner system, so there must be a reservoir providing them further out where the cold preserves them, and there are also two types of cometary orbit when considered in this way, one flattened like a planetary orbit and the other which can be at any angle to planetary orbits. The constant supply of comets has been used as an argument for a young Earth, so the alternative appears to be young Earth creationism unless some other idea can be arrived at. The objects comprising the Oort and Hill Clouds are the same as the planetesimals which originally formed the planets, and probably got thrown out of the inner system soon after their origin.
Inside the Hill Cloud is the Kuiper Belt. This is the outermost region of the system which can be directly observed. It extends from the approximate orbit of Neptune to about ten AU past Pluto’s average distance, and Pluto is part of it. It’s quite similar to the asteroid belt but much larger and contains much more mass. As soon as Pluto was discovered, its surprisingly small size and unsuitability as the planet which had disturbed the orbit of Uranus led astronomers to speculate that it was not the only world of that size and nature out there, and this was confirmed in 1992 CE with the discovery of the second “Centaur”. Centaurs, as the name suggests, are intermediate between asteroids and comets. The first, Chiron, was found in 1977 orbiting between Saturn and Uranus but at that time it couldn’t be said that it was more than just a large asteroid-like rock in an unusual place, but fifteen years later a second such planetoid was found and it quickly became clear that there was a large number of them in the outer system. This is the main reason Pluto lost its status as a planet: it isn’t that unique and if it had retained its planetary status this would’ve failed to recognise the importance of the many Kuiper Belt objects which orbit in that part of the system, often in quite eccentric orbits taking them 100 AU from the Sun.
The orbits of many of the known Kuiper belt objects beyond Pluto can be plotted to show that they are currently near their closest approach to the Sun, which suggests to me that many of them remain to be discovered because they are currently in parts of their orbits much further away. There are at least two types of Kuiper Belt object: classical and resonant. Classical objects are between 42 and 48 AU from the Sun and are able to orbit near the flat plane of the system further in. Resonant objects orbit in a certain ratio to Neptune’s year, which keeps it locked into Neptune’s orbit in a 2:3 ratio. Pluto is one of these, but all of these objects have roughly the same year length. There are also objects moving 60° ahead and behind Neptune in their orbits, and Neptune’s large moon Triton is thought to be a captured Kuiper Belt object of this kind. They also turn up elsewhere. An outer moon of Saturn, Phoebe, which orbits in the opposite direction to all the others, is thought to be such a capture too, for example.
As mentioned before, there may or may not be a large planet beyond Neptune, which would therefore be technically a Trans-Neptunian Object, and might also be orbiting outside the heliopause some of the time. Since the most common type of planet in the Galaxy, one intermediate between Earth and Neptune in size, seems to be missing from this system, it’s possible that one is around that far out which may have started further in. It was also hypothesised that there’s a much larger planet, provisionally named Tyche, is there. This has been evoked as an explanation for the asymmetry in Kuiper Belt objects, which tend to be on one side of the Sun rather than the other. Although obviously they orbit, their aphelia – the point in the orbit furthest from the Sun – are on one side. However, this has now been disproven by surveying the whole sky for such a planet, which was supposed to be four times the mass of Jupiter, out to 10 000 AU from the Sun. Another disproven theory was Nemesis, a red or brown dwarf star 1.5 light years from the Sun, blamed for mass extinctions occurring every 26 million years, which would correspond to its orbital period, but now there doesn’t appear to be such a cycle and it hasn’t been found. The surveys which eliminated the possibility of Tyche don’t refute the existence of a smaller planet up to 250 AU out, or with a highly elongated orbit bringing it between 400 and 800 AU out.
Sedna is a trans-Neptuian object around 1000 kilometres in diameter with an unusual orbit, and is incidentally the kind of object which might have been identified as a planet if the definition hadn’t been changed in 2006. It takes eleven thousand years to orbit the Sun and its distance varies between 76 and 937 AU, meaning that at its aphelion it takes sunlight more than five days to reach it. It may just be me, but this extremely elongated orbit strongly suggests to me that it’s one of many such objects which just happens to be close enough to be detected right now, but I’m not a professional astronomer, so maybe I’m wrong.
Turning to the outer planets, Jupiter and Saturn have a very large number of moons each. Some of them are minute. Leda, for example, is just eight kilometres in diameter. If their orbits were visible in the sky, both systems would look larger than the moon to us. Both of them also have three “bunches” of orbits, but of the moons known from before probes were sent Saturn’s Phoebe orbits a lot further out than the rest. Nowadays a further fifty-eight moons have been discovered orbiting Saturn beyond Phoebe, making a total of eighty-three. The much more massive Jupiter only has eighty detected moons. I don’t know why this is. Both planets have large magnetospheres with tails reaching behind them and consequently Jupiter has powerful radiation belts in which three of its four planet-sized moons, as opposed to the many more smaller ones, orbit within, making them extremely hostile. Both of these magnetic fields are generated by metallic hydrogen deep within the planets.
All the outer planets have rings. However, Saturn’s, the brightest, lightest and most prominent, are likely to be temporary. This is just me again, but I think rings are more likely to develop around larger planets because they’re larger targets for objects to be captured by and then broken up.
Inside the orbit of Jupiter is of course the asteroid belt. Although it used to be thought that it was a former planet which had broken up, adding up all the matter in the belt isn’t enough to make even the smallest known planet. The largest object within the belt is Ceres, whose diameter is around 1000 kilometres. The belt is not crowded or particularly dusty, and as I’ve already said the idea that it’s a hazardous rock-strewn region is completely inaccurate. Most asteroids are so far apart from each other as to be invisible to the naked eye from their surfaces. It’s been stated that Pluto deserves to be a planet because it has quite a few moons. The asteroid belt gives the lie to this because many of its members are piles of rubble loosely held together by their weak gravity and it isn’t unusual for them to have moons simply because the smaller lumps of rock can get dislodged and start orbiting. Asteroids are made of various substances. Some, such as Vesta, are bright and icy. Others are etremely dark and made of carbon, or they may be composed of iron-nickel alloy or stone. Their orbits tend to occur fairly close together in bands due to the action of Jupiter’s gravity, which pulls asteroids with periods in certain ratios to its own sidereal period (“year”) together. Elsewhere in the system, this may have been the main factor in causing the other planets to form. The Solar System has been described as “the Sun, Jupiter and assorted débris” because of the huge disparity between the masses of the two and everything else, even added together.
One asteroid, Hidalgo, is actually a centaur and has a very unusual orbit, more like a comet. It spends some of its time in the asteroid belt but its maximum distance from the Sun is almost as far as Saturn. Its orbit is also very tilted to the plane of the planets. As far as I know, no other object is like Hidalgo.
Within the asteroid belt are the four inner planets, five if you count Cynthia. Of these, Mars and Cynthia are only about sixty percent as dense as the others. Being close to the asteroid belt, Mars has captured two small moons from it, one of which, Deimos, is unstale and will be ripped apart by tidal forces in about 30 million years, after which it will form rings. Earth and Venus, as mentioned before, are twins, although Venus is exceedingly hostile to life and the hottest planet of all on its surface (Jupiter has the hottest interior). Mercury is the smallest planet. Neither Mercury nor Venus have moons.
Also in the inner solar system is a fairly large number of asteroids which periodically impact on the planets and other bodies within it. One of these, Icarus, has an orbit taking it out to the distance of Mars and to within 20 million kilometres of the Sun. Several asteroids have orbits locked to the planets in various ways, including Amor, Apollo and Eros, also the name of classes of asteroids with similar orbits in the case of the first two. Apollo asteroids cross Earth’s orbits, so astronomers tend to want to keep an eye on them, but due to the general disengagement people seem to feel with astronomy there is no proper monitoring program for them and no organised defence against them crashing into us and wiping us all out, and apparently that’s all absolutely fine for some reason. Amor asteroids, including Eros, a sausage-shaped object about the size of the Isle of Wight, have orbits close to that of Earth’s at perihelion and usually close to Mars at aphelion. They can also be hazardous, because the orbits of relatively small bodies tend to be less stable. Finally, Aten asteroids have average distances (semi-major axes is the official term) less than Earth’s from the Sun and an aphelion greater than Earth’s perihelion, so these too cross our orbit.
Impacts on the planets of the inner system regularly chip bits of rock off them, which may land on other planets. Consequently there are occasional meteorites on Earth from Mercury, Mars and Cynthia, and there are also many meteorites originating from the asteroids.
All of the known planets of the Solar System orbit in roughly the same plane and have almost circular orbits, the biggest exception being Mercury’s, which is roughly lemon shapes without the pointy bits. There isn’t much inside the orbit of Mercury, possibly because the sunlight is so strong there that it pushes everything away from it. Some of the larger planets have asteroids orbiting 60° behind and ahead of them in the same orbits as their own because the Sun’s and their own gravity balances at those points as well as four others. This provides a kind of transport system between the different planets, because rather than having to aim for the planets themselves, spacecraft could theoretically just aim for these “Lagrangian” points where the gravity between the various bodies balances and let themselves fall the rest of the way towards the planets. All the planets orbit in the same direction but two of them spin backwards compared to the others: Uranus and Venus. Jupiter, Venus and Mercury orbit more or less upright and Uranus is tipped over. The other planets are all somewhat tilted.
The Sun is a yellow dwarf about five æons old. Although it is called a “dwarf”, it’s actually in the top ten percent of stars by mass. By volume, it’s somewhat over a million times the size of this planet.For some unknown reason, its atmosphere is more than a hundred times hotter than its surface. It has an eleven year cycle during which its magnetic fields get wound up, shifting the number and latitude of sunspots on its surface. At the end of this cycle, it kind of goes “SPLI-DOINGGG!” and the magnetic fields straighten up again.
So that’s the Solar System, about which I will be going on and on for ages, but I will also be taking breaks and only doing it every other time. I tend to think of the bodies within the system not as asteroids, centaurs, dwarf planets and planets so much as gas giants, solid round objects and smaller irregular objects, so I’ll be dealing with them as that. There are somewhere over two hundred moons, eight known planets (nine counting Cynthia), four asteroids larger than Mimas (Mimas is an important borderline case for reasons I’ll mention eventually), eighty-four Kuiper belt objects including Pluto which are larger than Mimas, and a total of 932 centaurs, all of which are too small to be properly rounded. Some of these bodies are extremely boring or very similar to other such bodies, and there are also comets of course. Obviously I’m not going to write more than a thousand blog posts on all this, but I will probably be writing quite a few.
One thing I don’t know is whether there are more Star Trek episodes than interesting Solar System objects, so we’ll have to wait and see.
“Chauvinism” is quite an old-fashioned word for prejudice against a particular group. Nowadays each has its own word, generally consisting of the name of the type of group plus “-ism”. It comes from a Bonapartist soldier called Nicolas Chauvin, who insisted on maintaining his support for Napoleon after the Bourbon Restoration, and was then extended to apply to any type of fanatical devotion to or against a group or cause. In the light of the dangers posed by the use of the word “terrorism”, it might be worth bringing it out of retirement to refer to a particular kind of fanaticism which doesn’t currently have an obvious word to describe it, although “fanatic” is a less ostentatious option.
The use of “male chauvinist pig” apparently dates back to the 1930s CE. It has a rather old-fashioned tone to it now, but maybe it deserves reviving. For a start, it doesn’t lend itself to referring to sexism both ways, which is a contentious issue. It can only mean prejudice against women and girls. “Female chauvinism” is also used sometimes. A notable aspect of it is that it refers to the individual in the group to which there is a bias rather than a group, one member of which there’s a bias against. “Racism”, for example, refers to the category of race and not to a specific ethnicity, but very often refers to White racism against others, and this centring on the member of the group responsible for the prejudice is quite helpful conceptually. I don’t think “White chauvinism” is a common utterance, although there’s an interesting Communist pamphlet with that title dating from 1949, but it works quite well as a way of emphasising Whiteness and White fragility. However, the word has long since gone out of fashion in these uses.
A more specific use of the word “chauvinism” seems to have started with the well-known science populariser Carl Sagan in the late 1960s. He uses it to refer to biasses in ideas about extraterrestrial life. Examples would be “carbon chauvinism” and “water chauvinism”. The idea here is that a particular characteristic of life as we know it on this planet leads us to conclude that all life must have that characteristic, and this restricts the places and circumstances in which we might consider or look for other kinds of life. It might even affect how we view life on this planet because of the possibility of a “shadow biosphere”. It’s conceivable that even on, or perhaps in, Earth, there are other forms of life which don’t share our chirality or chemistry. For instance, the phenomenon of desert varnish, a dark coating which forms on rocks in arid areas, has been suggested as the action of undiscovered life forms which are not like the ones we know about, and a more outré suggestion is that silicon-based organisms live within this planet but never come anywhere near the surface. Carl Sagan, if I recall correctly, described himself as a carbon chauvinist but “not that much of a water chauvinist”. That is, he couldn’t conceive of a way biochemistry could emerge if it wasn’t based on carbon, although he did believe in the possibility of other elements substituting for some of our own. Here are a few entries from his Encyclopedia Galactica:
This one appears to have carbon, hydrogen and oxygen like us but lacks nitrogen, sulphur or phosphorus. It also utilises helium, which must be non-chemical. Germanium and beryllium also have no biological rôle on this planet, and it looks like this civilisation has no historical association with planets.
More details of the same explain further. They are not a single species but an alliance of some kind, perhaps symbiotic, and can apparently only survive in interstellar space because they depend on superconductivity, which only occurs at a low temperature.
This is us:
The last entry might be a bit depressing! This was in 1980.
I mention chauvinism now because I’ve had some difficulty wording my writing in this blog recently. There is an issue with the way we can refer to what I’m going to call “worlds” for argument’s sake in this paragraph. We tend to talk about planets as potential abodes for life, including technological cultures, but this is rather misleading. Considering our own Solar System, we have one body which is established to have had life on it for æons, our own Earth, but other worlds have been considered. At the moment the candidates seem to be: the upper atmosphere of Venus; the surface and oceans of Earth (quite a strong candidate that one!); Mars; the upper atmosphere of Jupiter; the interior oceans of Europa, Ganymede and Callisto; the surface and interior ocean of Titan; the interior ocean of Enceladus. There are a couple of weaker candidates in Ceres and Pluto. That gives us four planets, two dwarf planets and five moons. Hence even in our own system the possible places for life as we know it are mainly non-planetary, and constantly referring to “planets” in other star systems as places where life might evolve or appear without technological intervention starts to sound rather prejudiced. Maybe planets tend to be less suitable than other types of world.
The reason for most of these possibilities in our Solar System is that they have internal oceans. Europa and Enceladus in particular have rather suitable ones. Ganymede, Callisto and probably Titan also have liquid interiors but they’re more like Earth’s mantle than oceans, which might make them less friendly to life as the supply of other elements than hydrogen, oxygen and perhaps nitrogen might be very limited or non-existent. The geysers on Enceladus, on the other hand, do contain organic molecules with molecular weights above two hundred daltons, which is slightly larger than glucose, so the complexity may be considerable, and this is the only place off-Earth so far where such large molecules have been detected. Another very common finding, even in places where life is very unlikely, is tholins, which are reddish tarry organic substances present on many asteroids, centaurs, Titan, Europa, Rhea, Pluto and Ceres, although it isn’t clear that tholins are responsible for the red terrain on Pluto. Tholins are like the “cousins” of organic life forms, because they’re generated by the action of radiation such as cosmic rays on simple organic compounds. They’re bound to be common on small solid planetoids and comets throughout the Galaxy, and the question arises of whether we are the black sheep of the family in that we’re the rare exception, or whether life is just what happens instead of tholins in similarly widespread conditions.
It seems moons with sub-“terranean” oceans are a likely place for life to develop provided there’s an energy source and sufficiently varied elements, along with sufficiently low salinity. That last criterion may be surprisingly hard to satisfy. The total amount of liquid water in the Solar System is many times that found in our oceans, and the proportion of water on the moons involved is also much greater than that of the oceans to Earth. The energy source may be the Sun but is more likely to be tidal forces acting on the moon from surrounding large moons or the large planet it orbits, or it may be radioactivity as it is with our planet’s interior. If intelligent life arose in these conditions, it might be blind, unable to produce fire and unaware of anything beyond its ocean, since there would be a thick layer of ice above it. That said, it might also be tempted to drill a hole in that ice to see what’s outside or perhaps follow the course of a geyser or cryovolcano out into space, and it would be easier to leave most moons’ gravity wells than Earth’s, particularly as only Titan among these has a significant atmosphere, since they’re much smaller and less dense than this planet. It’s still possible that some kind of exothermic reaction could replace fire in their technology, but they might be stuck in the stone age if they exist at all.
I’ve already talked about exotic life in neutron and ordinary stars, which are of course not planets either, and there are also “rogue planets”, which wander through interstellar space too far from any stars to become associated with them. These will have been hurled out of star systems at some point, but life could possibly still arise on or in them if there is volcanism, or in any moons of the type mentioned if they’re tidally heated. In a sense these are actually proper planets, because the word planet means “wanderer”, which is what these do rather than orbit, which is what we tend to think of planets as doing. This actually means that etymologically these aren’t planets at all. Not only is Pluto not a planet, but nor is Mercury, Jupiter or Mars. In fact Pluto is in that sense more of a planet than the others because its orbit is more erratic and probably chaotic then theirs. However, it’s a fallacy to take the original meaning of a word as gospel and base one’s arguments on that, as can be seen with the idea that homophobia is misnamed because it’s hatred rather than fear. Maybe “heterosexual chauvinism” would be a better way to describe that combined with biphobia and panphobia.
There is also the question of what a technological species or perhaps intelligent machines would do if it got into space. In the mid-1970s, a plan for a rotary space colony about a mile in diameter (it was an American project, which might explain the units) situated at the L-5 gravitational equilibrium point between Earth and Cynthia was put together, and on this idea was built the expectation that if humans did move out into space, they might not actually be very interested in settling on, for example, Mars, when tailor-made orbital environments could be devised much more easily. It’s debatable whether such habitats are economically viable and the first would depend on the existence of industry on Cynthia to work, but there are different motives for going into space such as rescuing some, and that’s a very small fraction, of the species from a major asteroid strike or some other mass extinction-type disaster, and the motives of aliens would of course be unknown. Nonetheless it makes a lot of sense to bypass planets entirely and just build wheels in space, and beyond that perhaps Dyson spheres and ringworlds. Extending this far enough into the future, perhaps the most suitable places for habitation wouldn’t be found near Sun-like stars at all but the likes of blue supergiants like Rigel or the Pleiades rather than the likes of α Centauri or τ Ceti, because the former have very deep habitable zones and plentiful radiation. These are also the names that turn up in Golden Age science fiction because people have actually heard of these places. ETs might also board space arks, initially to get to nearby stars but take so long to get there that they no longer see the point of disembarking once they reach their destinations, and just carry on voyaging. There’s another answer to the Fermi Paradox: aliens leave their home worlds, establish colonies in space or launch spaceships to nowhere (leaving any place?) and their original abodes just go wild again. Also, we’re looking at the wrong stars for technosignatures.
There is one more really wild possibility: maybe life evolves in space and stays there. Life evolving in space isn’t a particularly new idea. Fred Hoyle and Chandra Wickramasinghe claimed in 1974 that the reddening of distant galaxies attributed to the expansion of space is in fact explained by microörganisms absorbing their light and they weren the first to claim that life here comes from elsewhere. More recently it has been noted that the whole of the early Universe had the right conditions for life, being fairly warm, dense and having all the right elements in close proximity to each other, for the kind of life we know about. Cosmic strings, of course, also existed by this point, so if that kind of life exists at all, it may have done so even before that happened. This is leaving out all the other possible kinds of life, such as plasma, and there have been thoughts about life based on liquid helium or superconductors, although I don’t know how that would work in detail. All of this is very vague.
To finish then, perhaps we think too much about planets when we consider alien life. It is in fact notable that we don’t seem to have a simple word to refer to heavenly bodies which are not stars in general. Maybe if we had a future, we would find ourselves eschewing both Earth and other planets just to live permanently in space and things here could go back to how they were before we evolved. They probably will anyway after we’re extinct. Meanwhile, maybe there are countless civilisations in the Universe trapped under heavy atmospheres or the bottoms of frozen over oceans in eternal darkness who don’t even know there is anything else, while out there between the stars are wraith-like beings thousands of kilometres across with their own societies, or living starships who evolved on their own. It has been said, after all, that the Universe is stranger than we can imagine.
A Box Of Chocolates 