By Any Other Name

What’s in a name? If you’ve been following this series, you probably have a good idea which planet comes next. I’ve done Saturn, its moons and the centaurs between Saturn and the next planet, so you will be aware that this leaves me with little choice but to post on the seventh planet of the Solar System, and the first one to be discovered since the invention of the telescope. We all know what its official name is, and how annoying that is.

I’ve already insisted on calling the large satellite which orbits Earth on which astronauts landed at the end of the 1960s CE and into the ’70s, which tends to light up our nights and occasionally covers the Sun almost perfectly, Cynthia. There were other choices, some of which may even have been better. I personally like Selene for example. In fact in that case there were so many choices that it was hard to make a decision. This is unsurprising, since any sighted person would be familiar with the body in question. Not so with this other planet, although intriguingly it is visible to the naked eye on occasion and in days of yore, perhaps even in the Palæozoic, it would’ve been clearly visible to many animals, so the usual statement that it was first discovered on 13th March 1781 is quite anthropocentric in a way. This opens up another much more remote possibility: were humans the first culturally-oriented entities to notice it, or did some starship come by back in the Proterozoic or something, and note its presence? The reason I mention this is that this planet is unusually afflicted by its current official name, and for us this is very significant.

The initial choice wasn’t much better. William Herschel chose to call it Georgium Sidus – “George’s Star” – after King George III. Today this seems like a weird thing to do and it took almost six dozen years for today’s name to be accepted. Garbled internet lore has it that it was called “George”, but this isn’t actually so. There were also a number of other names, but Herschel naming it after his patron seems divisive and not conducive to international coöperation in science. Then again, Virginia was named after Queen Elizabeth and so forth, so it was common practice during that long period of history, and there are also the Sidera Lodoicea.

There were other suggestions. One was actually “Neptune”! This was surreptitiously to celebrate British sea power, so maybe it is just as well that didn’t happen. Another possibility considered was “Oceanus”. Both of these refer to its green-blue colour as well as other things. Being the first historical instance of a planet being discovered, there seems to be an element of what TV tropes calls “Early Installment Weirdness” about the naming. People didn’t have a proper precedent as to what to do about a novel astronomical discovery of this kind. It was initially supposed to be a comet, since these had been encountered before. The moons of Jupiter and Saturn had established a precedent for naming after Greek mythical figures, and this was eventually followed. The planet was dubbed “Uranus”.

There seems to have been a long period in history during which names which are regarded as embarrassing and silly nowadays just weren’t. This applies in particular to surnames and this doesn’t even seem to depend on semantic drift. Whereas I can easily believe that a surname such as Pratt has only become potentially embarrassing recently, there are other names whose pedigree of ridiculousness must be much longer. I should point out here that my own surname is annoying and ridiculous in an English-speaking context, so maybe this has led to me focussing a lot more on this planet’s name than usual. It does seem to suggest that people’s senses of humour, if this can be regarded as more than puerile, change as time goes by. Just to state very clearly what the issue is, there are two ways of pronouncing “Uranus” in English. One is the older pronunciation of “your anus”, which I probably used up until about 1980, and the other, which initially seemed better, has turned out to be heard as “urine-us”. So you can’t win. One way or the other it’s gonna sound stoopid.

It might be thought that this doesn’t really matter. However, imagine you’re a NASA employee or an astronomer going up before some kind of board or committee holding the purse-strings and asking non-specialists, or just non-astronomers, for funding into a mission or research into this planet. One might hope that this would have no bearing on the success of such a bid, but it’s alleged that in fact there is less funding and focus on the planet than might be expected, and if that’s so, the name may not be free of consequences. Or, it could be that the planet and its moons are just harder to reach or less interesting than the other planets and moons. Jupiter and Saturn may be grabbing attention though, and this in itself could be connected to naming.

This planet is the first to be given a Greek rather than a Latin name in international nomenclature. In languages which use Chinese characters it’s known as 天王星, “sky king star”. This actually has the word “wang” in it in Mandarin, but unsurprisingly this is not a double entendre in that language, at least for what it is in English.

It doesn’t end there, although the next bit is a little less well-known. On the whole, moons, planets and asteroids within the system had been named from Greco-Roman mythology. This is quite questionable in some ways but typical of Eurocentric culture, and it extends to much international technical vocabulary, in the sciences and elsewhere. Steps have now been taken to name more recently-discovered objects in other ways, for instance from Inuit, Shinto and Norse traditions among others. Hence, for instance, ʻOumuamua and Sedna. Oddly, the moons of the seventh planet were an early example of a break with tradition which occurred nowhere else for quite some time although it was still Eurocentric. None of the moons have names primarily from European classical mythology, and they never have had, although many are Latinate in form. Instead, they’re mainly named after characters from the works of Shakespeare and Alexander Pope. The first two discoveries, by Herschel himself, are Titania and Oberon. Of these, the first is, I think, a poor choice, partly because it’s too similar to Titan and the associated adjective is Titanian, which many might confuse with the one for Titan, and partly because it tends to be pronounced in all sorts of weird ways such as “tittan-EYE-a”. Once that precedent had been set, two more moons were discovered in 1851 by Lassell – Ariel and Umbriel. Umbriel is, so far as I can tell, the odd one out name-wise, since it’s named after the “dusky sprite” in Pope’s ‘The Rape Of The Lock’. Kuiper continued the tradition in 1948 with Miranda. These are all the relatively large spheroidal moons. Voyager 2 then discovered ten more in 1985-6 when it visited the planet. By that time, Voyager 1 had manœuvred itself around Titan to get a better look and had left the ecliptic, so it would have no more planetary encounters, so it was entirely down to Voyager 2. These moons are named Puck (the sole moon discovered in ’85), Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind and Belinda. These were followed by Caliban and Sycorax in ’97, then one more moon from Voyager data two years later known as Perdita. The remaining moons are called Setebos, Stephano, Prospero, Trinculo, Cupid, Mab, Margaret, Francisco and Ferdinand. Not being an Eng Lit bod, I only recognise some of these names from Shakespeare but Sarada assures me that all of them but Umbriel are Shakespearean.

This, then, provokes a further couple of suggestions regarding the name of this planet. It still draws from European culture, but it also circumvents the “urine/anus” problem. It seems to me there are two possibly appropriate choices for Uranus here. One is to call it Shakespeare. This is problematic in that it’s then an entire planet named after a real person. The other, also a real person but fictionalised by Shakespeare, is to call it Hamlet, in which case it would go back to being named after a royal, based on the Scandinavian legend of Amlóði. This figure may or may not be historical. Hence this is my proposal, and by the way I probably won’t even follow it myself: change the name of Uranus to Hamlet. This would, so far as I can tell, completely solve the silly name problem, and I can well imagine someone sitting down in front of a board of some description and proposing a mission to Hamlet without a single snigger in the house.

Next time I will actually talk about Hamlet the planet itself.

The Death Star Moon

Mimas is special. In fact, I hope all worlds described in this series are special, but to me, Mimas is special. I’m no fan of ‘Star Wars’, so I note in passing that it looks a bit like the Death Star but may not go too much further in commenting on that. Or I might.

The Death Star is 160 kilometres in diameter, and apparently (I know little of the franchise) was replaced by another one 200 kilometres across. If that’s so, the scale on the above picture is approximately correct because Mimas has a diameter of 396 kilometres. That’s slightly smaller than mainland Scotland, although obviously its surface area is greater.

Do I need to say it’s a moon of Saturn?

Mimas is a kind of landmark in the Solar System, and in fact in terms of size generally. It’s the smallest body which has achieved approximately spherical shape by means of hydrostatic equilibrium. Most or all bodies smaller than Mimas are far from being round, and most or all bodies bigger than it are round. However, this isn’t inevitable, for two reasons. One is that objects smaller than Mimas can still just happen to be round, and considering the huge number of smaller objects there are, I wouldn’t be surprised if some of them just happened to turn out to be round by chance. It’s also possible that a larger body than Mimas could turn out to be irregular in shape due either to having lower density or being made of stronger materials. Vesta, for instance, is larger than Mimas but isn’t anywhere near as round. Taking this the other way, there can also be smaller but denser or weaker bodies which are round for that reason. An extreme example would be a neutron star, which would be only ten kilometres in diameter but would be so perfectly round it would act as a mirror. Another factor which might or might not come into consideration is surface tension. If an object made of liquid water were able to hold together in a vacuum, the chances are it could be a tiny fraction of the size of Mimas and still be spheroidal. Hence I can ask a question I don’t know the answer to: is the surface tension of molten lava sufficient to make a body spherical at a much smaller size than Mimas?

A few bits of maths can be done with this moon before actually considering anything else about it other than its rough shape and size. It has a surface area of 493 650 km2, slightly smaller than Spain, although the climate is somewhat cooler and there’s no rain at all, on the plain or otherwise. Its volume is 32.6 million cubic kilometres, which makes it less than a five hundredth the volume of Cynthia or five times the volume of all the water on this planet. And it is in fact substantially made of water ice, at a cold enough temperature that it will have contracted from the volume it would’ve been at freezing point.

Before the Voyager probes, nobody had any idea that Mimas looked like the Death Star, and since they got there in 1980 CE and ‘Star Wars’ started in 1977, there couldn’t have been any conscious inspiration, but it does make me wonder if these things sometimes happen in other ways, but I imagine this is not the kind of thing which comes up much in astronomy. Pioneer 11, with its poor camera, had approached the 400 km satellite to within 104 263 kilometres, too distant to pick out any details, even the absolutely bloody massive one of the enormous crater Herschel which is the first thing anyone notices about it. However, Voyager 1 didn’t get much closer than Pioneer 11 at 88 400 kilometres, and I don’t know about now but at the time only about half the moon was seen.

Herschel is a third the diameter of Mimas itself, with walls five kilometres high and a central peak six kilometres in height and twenty by thirty kilometres across. To scale on Earth, it would be wider than Canada. It’s centred on the equator, which makes me wonder if that’s significant. None of the other craters on the surface are more than fifty kilometres across. There’s also a distinctive distribution of craters, where more than an entire hemisphere only has small craters less than twenty kilometres in diameter and the other hemisphere, which of course includes Herschel, has larger craters. There are also valleys.

The name can be pronounced either “My mass”, which is what I say or “Me mass”, which is closer to the classical pronunciation. The way I pronounce the names of astronomical bodies reflects a time before I knew much about the way Greek and Latin were spoken and therefore I often say them as if they were English words. The adjective, a little surprisingly, is “Mimantean”, like “Atlas” and “Atlantean.” Mimas the mythological figure was the son of Gaia and born from the blood of Uranus’s castration. I’m not quite sure how they could be both.

Herschel is of course mainly flat, meaning that the horizon from anywhere on its surface is further away than the horizon at eye level on Earth. From the central peak it would be even further. This probably means that of any spheroidal body in the system, the central peak of Mimas is the record-breaking location for seeing the maximum portion of any world at something like a twentieth of the moon’s surface. From the rim, it’s possible to see all the way across the crater, a distance of up to thirty kilometres, but also, because the rim is raised five kilometres above the “geoid”, it’s possible to see the rim from more than twenty kilometres away. To some extent it’s mysterious that the moon managed to hold together at all from the impact which formed the crater. Although there are much larger impact basins elsewhere, only the one on Mimas has a practically flat surface because of the small size and low gravity of the moon.

The way Mimas moves suggests that it contains a liquid ocean, but some scientists consider this unlikely because the moon is so small one would normally expect it to be frozen solid, so it isn’t known for sure if this is so. It’s more likely that the reason is either that the core is not spherical, not at the centre, or that HersUnlike many other places, Mimas has no ray craters. These are craters whose rims have lines radiating out from them such as Tycho, as can be seen clearly on Cynthia. This is thought to be due to the extreme brightness of the surface, which reflects 96% of the light falling upon it, thought to be due to it being covered in the kind of frost found on Earth. However, there are chasms around ten kilometres wide, around one to two kilometres deep and up to ninety kilometres long. I would imagine these are cracks caused by the impact, and on another Saturnian moon, which I will cover in future, it’s thought that an impact broke the entire moon apart and it fell back together again. I would expect the same to have happened to Mimas, although its lower gravity might have stopped this from happening.

Mimas is at least sixty percent water ice. What isn’t is probably due to impact by non-icy meteorites becoming embedded and gradually sinking into the interior.

It has exactly half the orbital period of the more distant moon Tethys and orbits twice for every three orbits of the moon Pandora, which is a shepherd moon. It’s also responsible for the Cassini Division.

The only other thing I can think of is that the map of the moon’s surface temperature looks like Pacman.

Because I just spent two posts not talking about the Solar System, for reasons I hope make sense, tomorrow’s post will be about one of the most interesting moons of all: Enceladus.