The Liver Of The Solar System

We’re only here because of Jupiter. That statement is true for a couple of reasons, but it’s no exaggeration.

In spite of appearance and activity, I am of course a herbalist of twenty-three years standing, and you don’t get to be a herbalist without treating the liver. This is absolutely not homeedandherbs, which is effectively moribund, but Jupiter is our liver as a star system. The liver has many functions, but one important one is to detoxify and store toxins. Liver herbs are also associated with Jupiter in the melothesic system. Jupiter the planet performs a similar rôle in absorbing and “detoxifying” asteroids and comets which would otherwise pelt the inner planets, by attracting them to it and often literally absorbing them.

In July 1994 CE, Comet Shoemaker-Levy 9 impacted Jupiter, leaving temporary “bruises” like this one. Jupiter is in any case a big target, making it prima facie more than thirteen hundred times as likely to be hit by débris than Earth even leaving aside its greater gravity and larger Hill Sphere. Considering that, Jupiter becomes more than six thousand times as likely a target.

Jupiter is also responsible for Earth’s formation in the first place. Jupiter’s year lasts 11.86 times as long as ours. This means there’s a potential orbit just within ours whose objects orbit the Sun once every 361 days. This is so close to ours that Earth actually dips into it for a short time each December. Jupiter cleared that orbit of dust and rocks 4 600 million years ago, just marginally to one side because its orbit was exactly twelve times as long and almost every dozen years the protoplanets there were slightly tugged by its gravity. This led to a crowded ring of matter which was to become Earth. Hence in a second sense we are only here because of Jupiter. There isn’t anything special about Earth in that respect either, although the orbits of the other planets don’t work out as exactly. Uranus is close though – its year is close to seven times as long as Jupiter’s. I haven’t checked this out but presume that the ratios are something like 2 in 7 or something less obvious. Earth is the largest terrestrial planet though, and has the most straightforward ratio. It should also be borne in mind that Earth’s gravitational pull may have done the same thing and that the orbits of some of the planets may not be fixed. I haven’t worked all of this out yet.

I may have quoted this too many times, but the Solar System has been described as consisting of “the Sun, Jupiter and assorted débris”. This is a little misleading as Jupiter only has a mass of about a thousandth that of the Sun and all the rest of the matter in the system taken together has a mass of forty percent of Jupiter’s, which is not negligible. In terms of size, there’s a star, a planet about a tenth of the star’s diameter, and the rest. As mentioned yesterday, the Jovian moon system is like a mini-star system in itself and the magnetosphere reaches out almost to Saturn, making it bigger than the entire inner Solar System. From here, Jupiter is usually just slightly too small to make out its disc, but is easy to spot as a very bright star in the night sky, which can sometimes cast visible shadows. Venus is the only other body orbiting the Sun alone which can do that.

Jupiter gives the impression of turbulent and frantic behaviour, like a boiling pot of multicoloured paint. Olaf Stapledon compared it to streaky bacon, although that doesn’t do justice to the colours. Probably in the absence of the opportunity to find out much else about it, Jupiter’s stripes have been meticulously labelled, thus:

The general shape of the planet can be seen in this diagram: Jupiter is notably flattened at the poles and bulges at the edges. This is also true of Earth but in our case the planet is more or less rigid except for the atmosphere and ocean, so it’s only three permille wider at the Equator than at the poles, something I discussed in ‘For The High Jump‘. Jupiter, being largely fluid, is six percent wider at the equator, which is two-thirds the diameter of Earth itself. Saturn is even more squashed. It’s like someone sat on it. Geddit?

Being fluid, the planet doesn’t rotate as a single object but consists of System I, System II and System III, meaning it doesn’t have a single fixed day. In fact no planet has but that’s another story to do with fixed stars versus the Sun. System I is the equatorial rotation up to 9° latitude, System II the polar, actually everything further from the equator than that and is five minutes slower and System III the rotation of the extremely active radio signals from the planet. Additionally there’s the Great Equatorial Current, which is faster at nine hours, fifty minutes and 34.6 seconds, according to an estimate made in 1897. This is over twelve kilometres a second, compared to Earth’s equatorial velocity of 463 metres per second. This is the kind of frenetic and torrid environment Jupiter is. The whole planet takes a bit under ten hours to rotate. It also does so practically upright. There are no seasons. The Jovian year lasts 94 425 days according to the equatorial current rotation, but this is not a definitive figure because Jupiter doesn’t have one definitive day. This differential rotation also means there’s a lot of turbulence in the atmosphere between different latitudes, because they’re rotating at different velocities.

The problem of conveying longitude encountered with the Sun, that of attempting to find a fixed point on an essentially fluid surface, is also present here. No less than six systems exist for doing this. They’re significant because of comparing observations made by the various different space probes sent there since 1973. There is a second similar problem with Jupiter: where’s the surface? This and the other issue are characteristic of gas giants. The problem here is that you might say Earth’s surface is the bit we stand on, especially if we’re Jesus, but on Jupiter there just is nothing to stand on and although at some point there is liquid and solid in the interior, conditions there are so extreme that there’s about as much point considering it the surface as the core of the Sun. Most people go for the visible cloud tops, but sometimes you can see further down into the atmosphere than that.

The belts are dark, the zones light. Zone is actually the Greek word for “belt”. There are diverse variations within the belts and zones, but before I get there I should mention the elephant in the room, the Great Red Spot. This is a large oval 22° south of the equator, varying in width and drifts westward, which is a pity as if it didn’t it could be used as a marker for longitude. It also oscillates north and south by around 1 800 kilometres over a cycle of almost ninety days. First observed in 1664 by Robert Hooke, famous for his microscopy, the GRS may or may not be a persistent feature. It actually isn’t permanent. For instance, it disappeared completely in about 1980. It also fluctuates in size somewhat, but has recently been 16 350 kilometres east-west. Its nature and the reason for its colour are still unknown. The earliest idea was that it was a giant active volcano, which was at the time when Jupiter was thought to be largely a solid body. I don’t understand why they thought it was, though, because its density is easy to measure given the movements of the Galilean satellites and it clearly was not a massive lump of rock.

After the volcano theory was rejected, it was suggested that it was a large ovoid object floating in the atmosphere and bobbing up and down, because it appears to change in colour and size. Better resolution and lenses seem to have led to the realisation that it was some kind of anticyclone, being in the southern hemisphere, but this isn’t really an explanation because its persistence, size, location and colour are all puzzling. Two suggestions are that it’s a Taylor Column and a Soliton (‘Star Trek’ fans may have heard of that). A Taylor Column occurs when a rotating fluid meets an obstruction. Drag then forms a cylindrical structure. This would clearly require some kind of body floating in the atmosphere, or possibly in the liquid below it, and moreover an extremely large one considering the enormous strength of the Jovian gravitational field. A soliton is a wave packet which stays bunched together as it moves and is able to collide with other waves without losing its form. It’s hypothetically possible that solitons made of gravity waves (or possibly gravitational waves) could be used to achieve warp drives, but this isn’t relevant to the Great Red Spot, which is a fluid phenomenon, although I imagine that’s why it cropped up in ‘Star Trek’ (TNG – ‘New Ground’). It was first knowingly observed in a Scottish canal in 1834. They’re a bit like sonic booms. Solitons are generated in front of fast moving vessels in canals or rivers because of the horizontal and vertical restriction in the water. They’re like wakes moving ahead of an object instead of behind it because they have nowhere else to go. Once again, the idea of the flow being restricted is a little strange because it suggests the presence of solid obstructions, but maybe it’s more to do with the currents or turbulence being particularly markèd at those points.

There is another fascinating and mysterious aspect to the Great Red Spot which I don’t think has ever been explained. It occurs at the same latitude as several other phenomena on other planets. Olympus Mons on Mars seems to be caused by a hot spot in the planet’s mantle and is 20° north of the equator, and Hawaiʻi, caused by a similar hot spot, is also 20° north of the Equator, although in the latter case this is obscured by the movement of the Pacific Plate. Mars also seems to have drifted because the possible remnants of former moons which impacted its surface are no longer at its equator, which they should be given its current moons’ locations. Also, both of these phenomena are north of the equators rather than south of it. I’ve seen a diagram attempting to explain this by inscribing a tetrahedron one of whose vertices was at a pole, but I don’t know how relevant that is. Neptune has also had a dark spot 23° north of its equator but this may not be the Great Dark Spot as discovered by Voyager. It’s difficult to know if this is cherry-picking.

The other mystery about the GRS is its colour, which varies. Nobody knows what causes this. I find that somewhat surprising because I’d expect its spectrum to reveal its composition, but apparently it doesn’t. One suggestion is that it’s due to tholins generated by the action of solar ultraviolet light on acetylene and ammonium hydrosulphide. Another factor may be the greater altitude of the area. It is of course something like twice the size of Earth’s surface area. I don’t know if anyone has tried to correlate its changes with the activity of the Sun. It’s also colder than its surroundings, which is to be expected considering it’s higher up. It’s also extremely noisy, to the extent that as the sound from it travels up into the upper atmosphere it gets converted to heat and the region above the spot is 1 330°C. This may not be as spectacular as it sounds though, because temperature and heat are different. Low Earth Orbit, for example, technically has a very high temperature but it’s still freezing up there in the shadows.

There are other more transient spots, probably hurricanes, in the atmosphere, but weather systems in general are much longer-lasting in Jupiter’s atmosphere than ours because there’s no friction from a solid surface and also little variation due to the absence of land and liquid regions. Also, because the planet is so much bigger, so are the storms and other winds. Hurricanes often last decades. This raises the question of what weather would be like on a water world. If the figures relating to Jupiter’s axial tilt and surface are fed into a climate model for Earth, the result is a banded arrangement with persistent hurricanes, suggesting that conditions on such a planet, which might otherwise be habitable, could be quite hostile, and the weather conditions at particular latitudes would effectively constitute the climate because they’d be so stable.

Hydrogen and helium make up the bulk of the planet’s atmosphere, and therefore also the bulk of the planet itself, in similar proportions to the Universe in general and also the Sun. It managed to hang on to them because it’s colder on the outside and has such a high escape velocity. In 1939, the South Temperate Zone suffered a disturbance leading to the formation of a single white oval from four merging predecessors in 2000, which started to turn red in 2005. This time scale gives a good indication of how stable the weather is there. It’s also fascinating how Jupiter’s sheer size gives it a known history stretching back into Stuart times, which isn’t true of other planets except for Cynthia and Earth. Features on Mars were well-recognised but the occurrence of storms wasn’t observed until the nineteenth century, and Venus is just blank. This also underlines how dynamic the planet is compared to most others. The Jovian troposphere is somewhat like ours in terms of physical structure, with a falling temperature and pressure with height extending through clouds and leading up to a reversal and gradual increase of temperature marking the lower boundary of the stratosphere, then a mesosphere and thermosphere where the temperature is technically very high, but the chemical composition of the atmosphere is very different. It’s 90% hydrogen, 4.5% helium and has a significant amount of deuterium in it, though well under one percent. This compares to the one in six thousand atoms of hydrogen in Earth’s water. Deuterium also shows up in the compounds replacing the more abundant hydrogen. Methane, ammonia, water vapour, acetylene and phosphine are all present, as is carbon monoxide, but the really surprising constituent, though only present at less than one part per million, is the rather strangely named germane. Germane is like methane but has germanium instead of carbon in its molecules. Like many of the constituents of the Jovian atmosphere, germane would spontaneously ignite in our own. I don’t understand why there’s germane there. Germanium is not a particularly common element and its silicon analogue silane might be expected to be more widespread but it isn’t there. Germane is also denser than methane or silane, so its presence in detectable layers of the atmosphere is peculiar. I don’t think it’s found on any other planet. Incidentally, the presence of phosphine may not be a clue for life existing on Jupiter because the planet’s chemistry is not like that of Venus and conditions are very different. Here, it’s probably formed under high pressure much further down and churned up by convection currents. Methane is no surprise, and the carbon monoxide is probably the result of oxygen being relatively scarce in the original part of the solar nebula from which the planet formed.

You know that bit in ‘Fly Me To The Moon’? “Let me see what spring is like on Jupiter and Mars”? Well, whereas there are seasons on Mars, there are none on Jupiter, so it ain’t gonna happen. This is because Jupiter’s axial tilt is only 3°, so it basically has no seasons, although the butterfly effect might come into play. I suspect this is for two reasons. Firstly, Jupiter is the original planet in this system, so it probably determined the positions of the orbits, and secondly it’s so massive nothing could knock it off-kilter, so it ends up with a tiny tilt. In fact it’s surprising it tilts at all. If it did have seasons, each would last almost three years. Some people draw a link between the traditional Chinese cycle of twelve animals and the Western Zodiac because the planet spents around a year in each sign from our perspective. It should be pointed out that the strict 30° division of the ecliptic used in Western astrology doesn’t correspond to the actual portions of the zodiacal constellations in the ecliptic, and as is practically common knowledge nowadays, Ophiuchus is also in the circle and is ignored for astrological purposes. In the astronomical zodiac, Jupiter is currently in Aquarius but I don’t know how closely this corresponds to the astrological ephemeris, and it’s about to be the Year Of The Tiger. The orbit around the Sun is thrice more eccentric than ours at almost five percent, so there is a little variation in how much radiation and therefore heat Jupiter gets from the Sun.

However, Jupiter actually generates twice as much radiation as it receives, so there’s another reason it has no seasons: it’s actually warm itself, or in fact hot. This is because it’s still hot from the formation of the Solar System, since it has more than a thousand times the volume of Earth but only about 130 times our surface area, and possibly because it’s still contracting, although the contraction may be caused by the cooling rather than the other way round. At the core, the temperature is 20 000 K or higher, more than three times as hot as the Sun’s photosphere and almost as hot as solar flares, with an internal pressure of forty-five million times that of our atmosphere. There are two rival theories about the centre of the planet. One holds that there is no core in the sense of a solid rocky globe, but the planet just gets denser and denser towards the centre, and the other, more popular theory posits the existence of an Earth-sized rocky core. Somewhat away from the centre is a deep layer of liquid metallic hydrogen. Under very high pressures, various gases, such as oxygen and xenon, become metals. This may constitute up to 80% of Jupiter’s radius, and is responsible for generating the enormous magnetic field. The pressure here is a “mere” three million atmospheres and the temperature 11 000 K, so it’s still hotter than the Sun’s surface. Above this layer is molecular liquid hydrogen, twenty-five thousand kilometres below the clouds. The temperature finally drops below that of the Sun three thousand kilometres below the “surface”, where the pressure is ninety kilobars. A thousand kilometres down, the hydrogen becomes gaseous and the temperature is only around 2 000 K, then it falls to -143°C at the cloud tops. The magnetic field generated by the metallic hydrogen is about ten times the strength of Earth’s at this level, but it’s at an angle of almost 11° to the axis of rotation. All of this pressure stuff is exacerbated by the fact that Jupiter’s gravity is over two and a half times ours.

Jupiter has jet streams like Earth’s, but because of the coloured clouds, the white ones being mainly frozen ammonia, they’re more vividly colour-coded than ours. A jet stream is a relatively narrow, fast, horizontally undulating air current moving east to west and drifting north and south assuming the planet spins prograde. They’re formed by the Sun heating the atmosphere. There are four such streams on Earth, two subtropical and two polar. On Jupiter they’re driven by internal heating. Moving through the latitudes, there are alternating regions of faster and slower east-west winds, each of which is a jet stream, even though models show fewer jet streams on larger planets. Each stream is also “rolling”, in that it is a kind of horizontal whirlwind separated from its neighbours north and south.

Zones have more ammonia than belts, hence their paler appearance – they’re cloudier. The belt clouds are lower and thinner, and belts are warmer than zones. This makes sense if you think of ammonia condensing or freezing out of the atmosphere. I get the impression on looking at pictures of Jupiter that the belts look lower and possibly have shadows cast upon them by the clouds in the zones. Air seems to be warmed and rises in the zones, causing clouds to form as it expands and cools. In the belts, it sinks, becoming warmer and losing its clouds. The air flow generally tends to “stay in lane”. It doesn’t deviate in latitude much except within its belt or zone. At the poles, there are large circles in which not much seems to be happening. These caps can extend further towards the equator or less so, and the northernmost two bands after the north polar region can become incorporated into them temporarily. This extends to the NNTB (North North Temperate Belt), which can fade entirely, as it did in 1924. Consequently the NTZ varies in width. South of that, the NTB often has dark spots on its southern edge. The North Tropical Zone, NTrZ, is where the System I movement of the atmosphere comes uncoupled from the more polar System II. This leads me to ponder whether the planet consists of a series of nested hollow cylinders, such that the temperate regions north and south are in fact continuous but hidden under the more equatorial regions. They wouldn’t be homogenous in properties of course because the conditions deeper in the atmosphere are bound to be very different. Also, the liquid hydrogen ocean is not that far beneath the cloud tops.

The largest region on Jupiter is the EZ, or Equatorial Zone, with an area about an eighth that of the whole planet. That’s eight thousand million square kilometres, making it the largest visible feature in the entire Solar System. It’s something like six or seven times the entire surface area of all the inner planets taken together. While I’m at it, Earth mapped onto Jupiter would be the size of India on a map of Earth. There are many features in the EZ compared to most of the rest of the planet. For instance, it often shows plumes from its northern edge projecting southwest. A narrow belt appears occasionally at the equator itself. The southern side includes a “dent” where the Great Red Spot begins. The GRS itself is a feature dominating the South Tropical Zone, and this raises the question of why it’s in the southern hemisphere without any corresponding feature in the north. then again, the bands are not symmetrical either side of the equator either. The only thing I can think of right now is the very slight tilt of the planet combined with its greater orbital eccentricity creates slightly different conditions in the northern and southern hemispheres.

The planet emits decametric radio waves. This is of the order of thirty megahertz but they peak at seven to eight megahertz, so it’s close to the analogue VHF band used for FM radio on Earth, though the frequency is slightly lower. There are amateur radio projects monitoring Jupiter’s radio transmissions, which were discovered in 1955. Since they’re stronger in some parts of the planet than others, they provide fixed points enabling longitude and a “true” rotation period to be determined, but they aren’t associated with any visible features. They’re also polarised, like visible light passing through the plastic in front of a flatscreen monitor – they vibrate only at a fixed angle. This is due to Jupiter’s magnetic field and the charged particles moving within it. One of the moons, Io, influences the radio transmissions but I’ll talk about that more when I get to it. The decametric transmissions occur in short bursts sporadically. They last between a few minutes and several hours.

There are also decimetric waves, and these are continual and don’t have peaks at particular frequencies within that wave band, which is in the UHF range now used by mobile phones and previously by analogue PAL TV. They’re differently polarised and emitted from the volume around Jupiter. They’re synchrotron radiation, caused by charged particles moving in curves somewhat like the centrifugal effect, and show there are electrons moving almost at the speed of light. From Earth’s perspective this radiation fluctuates up and down according to whether we’re facing the planet’s magnetic equator or not.

This image is a painting made for Carl Sagan’s 1980 TV series ‘Cosmos’ and will be removed on request. As well as providing a fairly accurate image of what the planet looks like at cloud top level, it also illustrates Sagan’s speculations regarding life there. Although I am restraining myself from commenting on life elsewhere in the Solar System, the image without the organisms is still interesting. There are diffuse crystals of ammonia in the blue sky creating a halo around the rather smaller-looking Sun. A vortex can be seen towering over the scene to the left, with a bank of white clouds to the right, and there are a number of smaller vortices visible. Then there are long, almost straight clouds winding off into the distance, and of course on Jupiter the horizon would be several times further away than on Earth at around fifteen kilometres, although the clouds make it difficult to judge. Sagan proposed three ecological niches of organisms. There are “sinkers”, aerial phytoplankton which survive by photosynthesis and gradually sink into the depths of the planet, reproducing as they go until conditions kill them, “floaters”, somewhat jellyfish-like and balloon-like floating herbivores several kilometres across who can be seen in this image, and “hunters”, one of which can be seen at bottom right, who have a kind of retro, 1930s quality to them but look a little like Art Deco biplanes with round heads and sharp projections at the front. Asimov and Arthur C Clarke both believed that Jupiter was actually even more suitable for life than Earth, although the former’s belief was based on an earlier model of the planet which posited a vast, deep ocean beneath the clouds.

Right, so that’s Jupiter. I’ll probably do Io next.

The World Ceres

Title nicked from Asimov.

On the first day of the nineteenth century CE, the astronomer Giuseppe Piazzi pointed his telescope at an area of sky in the hope that Bode’s Law wouldn’t fail him, and indeed found the first independently-orbiting body within the orbit of Saturn since ancient times. This was in spite of an organised posse of astronomers, the “Celestial Police”, searching the heavens for such a planet. They were later to find more, but Piazzi, who had actually been considered for membership of this group, beat them to it. This was the world later to become known as Ceres.

Bode’s Law is the rather unfairly titled principle which appears to determine the distances of the planets from the Sun. It was actually first arrived at by Johann Titius some time before. It uses the sequence 0, 3, 6, 12, 24, . . . , to each of which four is added, giving 4, 7, 10, 16, 28, and has been fairly successful in predicting the positions of various planets. It was popularised by Johann Bode, hence the name. The units amount in this case to tenths of an AU, which is the distance between Earth and the Sun, as is seen in Earth’s position in this series at 10. The series isn’t perfect. For instance, it’s anomalous that it starts at zero and Uranus doesn’t fit, although Neptune does. Nonetheless, astronomers noticed there seemed to be a gap at 28. Mars is 1.524 AU from the Sun on average, with an aphelion of 1.666, whereas Jupiter averages out at 5.204. Astronomers used the sequence as evidence for another planet, and they found it.

However, the planet they found was rather odd compared to the others known at the time. The smallest known planet in the eighteenth century was Mercury, now known to have a diameter of 4 879 kilometres. Ceres is much smaller than this at 946 kilometres. During my lifetime this figure has been revised several times, so I imagine it was different in the early nineteenth century too, but in astronomy books at the time, Ceres is clearly shown as much smaller than the other known planets, yet still acknowledged as one, before the asteroids were discovered.

Over the next few years, a number of other bodies were found between Mars and Jupiter, and the planets were split into the categories of major and minor planets to account for them. Ceres was relegated to the status of a minor planet or asteroid for a long time, up until the decision to redefine planets in 2006 as mentioned here, at which point it was put in the same category as Pluto, a “dwarf planet”. As I’ve said before, I’ve never really understood why there needed to be such a category when that of “minor planet” already existed, but it did at least put Ceres in the same pigeonhole as Pluto, which was some kind of progress. It’s an interesting history though, because it means its tale with us began as a planet, stopped being one and then became one again. Also, in the light of what I’ve said previously, nowadays it could even simply be seen as a planet.

Ceres is not like the asteroids, even though it orbits among them. It conforms to the second 2006 criterion of planethood in being round due to its gravity. No other asteroid is so close to being spherical and the margin is actually quite sharp. The next closest seems to be Hygeia. Taking all known bodies in the system into consideration, the smallest round one is Mimas, which orbits Saturn and has a diameter of 396 kilometres, although it has an enormous crater which prevents it from being perfectly round. It isn’t “lumpy” though. Hygeia is actually larger than Mimas with a diameter of 444 kilometres, and is in fact a candidate dwarf planet in itself. There could be much smaller asteroids which are round, but if so this wouldn’t be due to their gravity.

The planet, for that’s what it is really, is the smallest in the system which orbits the Sun independently, but it also contains the bulk of the mass of all bodies between Mars and Jupiter, at about 30%. This means that even if the hypothesis about a lost, shattered planet there had been correct, or if Jupiter was in a different place and the mass of the asteroid belt had been able to assemble itself into one, it would still be smaller than Mercury or even Cynthia. Because it’s long been dismissed as an asteroid, Ceres has occupied a kind of second-class place in the system for a long time and consequently I for one, and presumably most other people who have learned abut these things, can’t easily reel off a list of statistics and facts about the planet as I would with, say, Uranus or even Pluto. I know its day lasts nine and a bit hours, that it has a very thin atmosphere indeed, not really even worth mentioning, but I don’t know its largest craters, axial tilt, how long it takes to orbit the Sun, highest peaks, climate or any unusual features. I do know that it has more water ice as part of its actual internal structure near one of the poles and that it has some water ice on its surface.

The distance from the Sun is kind of “unusual”. In fact it isn’t unusual at all as the zone Ceres occupies in its orbit is the most crowded of any in the system. However, because we haven’t tended to think of Ceres as a planet, and to be fair it is still something of an outlier as far as planets directly orbiting the Sun are concerned, we haven’t considered what happens at this distance. The main consequence is that it has an unusual range of surface temperature, between -163 and -38°C, which means that at its warmest its temperature overlaps with Earth’s. In other star systems there are probably larger planets in this kind of orbit because of other characteristics being different, such as no giant planets or giant planets in different positions, but for our system this is notable for being intermediate between the coldest (on average) terrestrial planet and the warmest gas giant. If it had the same atmospheric pressure as Earth, Ceres would be able to have liquid ammonia on its surface which could both freeze and evaporate, and the chances are there’d be an ammonia cycle like our own water cycle, along with rivers, lakes, rain and even snow and glaciers. However, in reality there’s practically no atmosphere. Even so, ammonia is rich on the surface and participates in the planet’s geochemistry, which suggests that it originated far out in the outer system where the compound is more abundant. There are clays rich in ammonia and ammonia salts in some of the craters. There is also the intriguing ammonium ion, NH₄⁺. This is distinctive in both bearing a single positive charge and being about the same size as some alkali metal ions, meaning that it behaves as if it’s a metal ion like sodium in sodium chloride, and can even form amalgam with mercury and sodium like solid metallic elements. In other words, it can form into metallic alloys even though it isn’t itself a metal. Due to all this, the geology of even the surface of Ceres is unique, at least for the more reachable part of the system. I may be wrong about this but I think of it as a clay-covered place, except that instead of water making it moist, ammonia does that job instead, and also unlike water (although the hydronium ion is common in the Universe, which is to water as ammonium is to water) in that it behaves a little like an alkali metal.

The asteroid belt divides the five inner terrestrial from the five traditional outer planets (gas giants plus Pluto) of the outer. Hence Ceres can be thought of as the middle planet of the Solar System, or to put it another way, central to it. This is not literally true because as the Titius-Bode Series shows, the planets are each almost double the distance of their predecessors from the Sun counting outward. This means that its composition and temperature are intermediate. It may or may not have a global ocean under its crust. This may have existed but will now have frozen. It would be possible to detect because it would be salty and this would make it detectably magnetically.

There is a single remaining extinct cryovolcano on the surface called Ahuna Mons, which is five kilometres high. At some point I will need to address what counts as height on planets without bodies of liquid on their surfaces. In this case there’s a clearly visible crater next to the mountain, Occator Crater, and it wouldn’t be sensible to assess its height from the bottom of that crater although it might influence its structural integrity. There are white streaks on the slopes like lava flows, and also like the white patches elsewhere on Ceres, all of which are probably salt. Incidentally, although “salt” brings sodium chloride to mind, I can’t find out whether this is the salt in question or whether it’s ammonium chloride, which is also white, or something else. It could be a mixture, but that’s my speculation. There are also possible traces of smaller volcanoes. There’s a concentration of mass about thirty kilometres below it, which suggests it was formed from a plume of mud rising from the mantle (which was probably watery). There’s also sodium carbonate (washing soda) on the slopes, which is found on Earth in desert regions as the mineral natron, used in the Egyptian mummifying process and to make glass. Ahuna is almost exactly opposite to the largest impact crater, Kerwan, suggesting that it may have resulted from shock waves moving around the planet and concentrating on the other side, where they fractured the crust. This happens a lot with large impacts. For instance, Caloris Planitia on Mercury is opposite so-called “chaotic terrain” on the other side, and in fact this is making me wonder right now what was opposite Chicxulub when the impactor hit, killing the larger dinosaurs.

Occator, next to Ahuna, has the largest concentration of bright spots. I have to say, looking at images of all the large bodies in the Solar System, Ceres is distinctive in having small white areas fairly sparsely distributed across its surface. These have been named faculæ, meaning “little torches” in Latin, a name first used to refer to bright spots on the Sun’s photosphere. They’re near ammonia-rich clays and are rich in magnesium sulphate, which is Epsom salt, so the whole planet has a kind of domestic chemical theme going on. These are on a hill in the centre of the crater called Cerealia Tholus, and at this point it’s worthwhile mentioning the name. Ceres is named after the Roman goddess of arable farming, after whom cereals are named. Ceres is known substantially for her daughter Proserpina, more often known by her Greek name Persephone, who was forced into marrying Pluto and living in the underworld, but finding that she could return provided she didn’t eat any food there. However, she ate three pomegranate pips and is therefore condemned to spending a third of the year there. Ceres mourns this by causing winter, and celebrates her return to the upper world with spring. The Greek equivalent of Ceres is Demeter, after whom a moon of Jupiter is called although this was renamed in 1975. Thereby hangs a tale, incidentally: Jupiter’s smaller moons all got renamed in the mid-’70s. The whole domestic flavour of the place is once again confirmed by the mention of cereal. This is a planet made of washing soda, ceramic (kind of) and Epsom salts named after the goddess of cereal! The rare earth metal cerium, discovered two years later and now used in lighter flints and the subject of an essay by Primo Levi, is named after the planet, rather like uranium, neptunium and plutonium.

Occator is unusual in having a central hill. This is normal on many craters on other bodies, but Cerean craters tend just to have dents in the middle. The largest crater is the previously mentioned Kerwan, one hundred and eighty kilometres in diameter. It isn’t clear if it had a central peak because a smaller impact has created a crater where that would be. It’s named after the Hopi cereal nymph, this time for sweetcorn.

Zooming out a bit and treating it as a planet like any other, as opposed to the asteroid it was formerly presumed to be, Ceres averages 2.77 AU from the Sun, approaches it most closely at 2.55 and has an aphelion of 2.98, which makes its orbit slightly less elliptical than Mars’s at 0.0785. It takes somewhat over four and a half years to orbit the Sun and is inclined 10.6° to the ecliptic, which is greater than any other planet out to Neptune unless you count the moons of Uranus (see the post on planet definitions if you don’t get why I’m calling them planets rather than just moons), though less than twice that of Mercury. Looking at the three planets Earth, Mars and Ceres as a, well, series, there is a trend of reducing size. Mars bucks the apparent trend of increase in size up to Jupiter followed by a decrease in size out to Pluto, but if Ceres is included a new possible tendency is revealed, also reflected in reducing density as Earth is over five times as dense as water, Mars and Cynthia around three times as dense and Ceres a little over twice as dense. This may just be playing with numbers, but it’s also possible that Earth hogged all the material, only leaving a few leftovers for the planets closer to Jupiter’s orbit. As for density, the closer planets to the Sun would have been warmer when they formed and this seems to have caused the icier components, or simply those with higher melting and boiling points, to evaporate off. However, Ceres seems to have formed in the outer system. It has an axial tilt of only 4°, so ironically the planet named after a goddess closely associated with the seasons has no seasons of its own. Surface gravity is less that three percent of ours, so if I went there I’d somewhat exceed my birthweight but only because I was small for dates.

Looking at the planet and knowing that most of what I’m seeing is clay puts me in mind of the idea that Ceres has an affinity with the various planets which show up in claymation shows. I can imagine its appearance turning up on someting by Aardman Animation, and it makes me wonder what the Clangers planet was originally made of. However, this is largely in my mind. It’s all very well looking at an image of Ahuna Mons or the planet as a whole in full knowledge that it’s mostly salty clay and seeing it like that, but on the other hand many of the craters are æons old and don’t seem to have sagged in all that time, although they do lack the central mounts found elsewhere. It may be more accurate to think of the planet’s surface as being made of frozen clay rich in ammonia, and it also isn’t clear what clay’s like if it’s mixed with liquid ammonia and well below freezing point as opposed to the stuff we make pots out of. I think Ceres may be the kind of place where our intuitions based on how things are here, or even in the outer system, may mislead us. That said, the edges of the craters are less well-defined and the floors are smoother, and when it was actually being hit by something it would presumably have melted or boiled the material, so at that point maybe it does behave like clay or go through a phase of clay as we know it as it cools down.

Although it doesn’t have an iron core, the planet is likely to have a core high in metals, but also in silicate rocks. The pressure on it will be far lower than on Earth’s core. Our planet is close to 6 371 kilometres in radius, more than twice as dense as Ceres and has thirty times the gravity. Put all of those together and it makes the pressure at the core something like (and these are back of the envelope calculations) what it would be only ten kilometres down in our own crust, or even less. This is only the level of an ocean trench and only a few times deeper than the deepest mines. Consequently the settling out effect of the originally molten planet is milder and not so influenced by pressures beyond easy imaginings. Outside that core is a mantle of silicate rock which may have squeezed out the water and ammonia, or they could have separated out due to being lighter. Above that is a probably frozen solid ocean, and finally on the surface lies the clay-rich crust with salty deposits. All this notwithstanding, it’s also been accurately described as “icy, wet and dark”, i.e. it has a dark surface. It isn’t particularly dark as far as sunlight is concerned.

There are several more ways in which Ceres is special. It’s a survivor from the early Solar System, in that it’s a protoplanet. Near the beginning, there would’ve been hundreds of small planets like this, large enough to undergo interior melting, which mainly happens due to radioactivity, and therefore stratification like Ceres has, but many of them would have collided with each other and stuck together, possibly been thrown out of the system entirely by close encounters with others accelerating their movement. Along with Vesta, which is more battered and smaller, Ceres is a surviving relic from shortly after the Sun formed. It’s also the closest dwarf planet to Earth, the first dwarf planet to be visited by a space probe, the first time a space probe had orbited two bodies on its mission and the largest body except Pluto-Charon not to have been visited up until 2015.

The spacecraft which visited it is also quite interesting. It’s called Dawn, and was actually launched at dawn one day in 2007. It used Mars to accelerate its path and visited and orbited Vesta, also a first, in May 2011. Vesta is interesting in itself, and I’ll be covering that soon as well. It then left Vesta and made its way to Ceres, becoming the first spacecraft to actually orbit two bodies in the Solar System unless you count the orbits made of Earth before some spaceships have headed off into the void. It’s still orbiting Ceres but its mission is now over. Dawn was also the first craft to use ion drive, an idea for a very efficient but slowly accelerating engine which can accelerate vehicles so fast they could cover the distance between us and Cynthia in less than two hours, without using gravitational assist, which is the usual reason space probes are accelerated to this velocity and beyond.

There is plenty more to say about Ceres, but I want to finish as I started: with the pun. Isaac Asimov used to be very fixated on puns, and several of his short stories were only written to make puns. In the case of his article ‘The World Ceres’, published in 1972, he may have been primarily motivated to write it just because he could use a good pun in the title. I have read it but I don’t remember how much detail he went into. It doesn’t seem likely that much was known about it at the time, but I may be wrong. It might be interesting to compare factual articles on astronomy before and after they were visited by probes. For Ceres, this period was a lot longer than usual, but also occurred only 206 years after it was discovered, which is pretty good going.

. . . Not As We Know It . . . Captain

If your first language is English and you’re over about thirty-six, I’m guessing, you may well remember this song. If you’re a bit older you’ll also remember their song about Arthur Daley, and you’ll also know who that was. I only realised recently that there was a claymation video for it though, because in 1987 CE I wasn’t watching television, with the exception of the repeat of ‘The Hitch-Hikers’ Guide To The Galaxy’.

One of the oft-repeated lines, alleged to be a quote from the original series, was Spock saying “Well, it’s life Jim, but not as we know it. . . Captain”, with a distinctive pause at the end of the verse before the Spock impersonator says the final word. It won’t surprise you to know that just as Kirk or anyone else never said “beam me up, Scotty”, this is a misquotation. The closest Spock comes to saying it is “no life as we know it” in ‘Devil In The Dark‘, when in fact he says it twice, and that episode in particular refers to a very common suggestion regarding “life, Jim, but not as we know it” – silicon-based life.

I have already discussed this here:

Without re-watching the video, my conclusion was that there are two ways in which life which could be said to be silicon-based are possible. Because silicon compounds are often bioactive, and silicon-based structures do exist in organisms on this planet, a situation could arise where much of an organism’s biochemistry involves silicon compounds, even including hormones and much of the hard parts of their body, but at core still carbon-based. The alternative is that a narrower range of silicon compounds which are however particularly versatile could be used in a manner similar to the difference between binary and higher-based ways of representing numbers. It can still be done, but the binary representation of the number eleven takes four bits but only one duodecimal digit. Hence silicon-based life could still exist but be more “long-winded” than carbon-based, and consist of relatively larger molecules than the already very large macromolecules found in terrestrial life such as muscle protein and cellulose. However, although I think it’s likely to be possible, I don’t think it would emerge of its own accord or be able to survive outside a specially designed environment, mainly because silicates are very stable compounds and once silicon has entered such a state it would be difficult to remove it. If you watch an exposed microchip under a microscope, you can see it visibly degrading and not-so-gradually oxidising. An environment containing silicon-based life of this kind would have to be free of oxygen and water. Silicon in water liberates hydrogen and combines with oxygen to become silica, and this may not happen with the silicon compounds used for life, but there’s a risk of producing bonds which are so strong that ordinary biochemistry can’t sever them all the way through silicon-based biochemical pathways.

Only the lightest atoms are able to produce more than single bonds. This includes boron, carbon, nitrogen and oxygen. As far as I know, no heavier element is able to form more than single covalent bonds. This means that the structures of molecules made up of chains or rings of silicon atoms may be rather limited, although silenes do contain double silicon bonds. Moreover, the stability of longer chains of silicon atoms is lower than that of carbon chains with the same number of atoms in them. Nonetheless, I do believe silicon-based biochemistry is possible and I will now cover some of the possibilities.

By Zephyris – Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15027555

DNA is a well-known helical polymer used to store genetic information. Silicates have various forms, consisting of sheets of hexagonally-arranged silica tetrahedra sharing vertices, alternating such tetrahedra with opposite orientations, simple chains of the same, or helically-arranged such chains. This is interestingly close to DNA, although it’s only a single helix and the unit is silica groups. There are also double chains known as amphiboles, linked via shared oxygen atoms. Some asbestos minerals are amphiboles. If these are able to form extra bonds with bivalent atoms of various kinds, the result would be a very similar molecule to DNA, with a potentially readable code, although how it would come uncoupled, be transcribed, what it would be transcribed into, and how it could replicate and recouple are different questions, which may not have answers. Nevertheless, this is a potential storage medium, perhaps one which would need to have more “steps” than DNA per codon. This illustrates what I mean by molecules needing to be relatively larger, although on the other hand the actual rungs are smaller because they only consist of two atoms.

Closer analogues with organic compounds are the silanes and silanols. The former are silicon-based versions of the alkanes such as methane, butane and propane. Like them, silanes are flammable, and become more flammable the longer their chains are because longer chains are less stable. In the case of alkanes, similar substances can be derived from them in the form of long-chain fatty acids, with a -COOH group on one end. These are just ordinary organic acids which happen to have very long chains, and in organisms they’re often joined together by a glycerol residue at one end into kind of E-shaped molecules, used to store energy and form cell membranes. Eicosapentanoic acid is quite a well-known essential fatty acid. It has mixed double and single bonds, like all polyunsaturated fatty acids, and twenty carbons per molecule. By contrast, the highest silane has only six carbons, and is entirely saturated because they only have single bonds.

Silanols are the silicon-based versions of alcohols, although many of them are in fact organosilicon compounds rather than containing no carbon. They’re more acidic than their organic equivalents and can be used in shampoos to improve the pH balance of the scalp and hair. Another class of silicone compounds in common use is the cyclosiloxanes, which are hormonally active, found in cosmetics and toiletries and are persistent in the environment. As far as this particular biosphere is concerned, these substances are concerning, but their bioactivity suggests that in other circumstances they could be functional as biochemicals. Many of these contain oxygen bonds, which may be why they aren’t broken down. It may not be that they are merely difficult to process in organic biochemistry, but just difficult to do so in any circumstances conducive to chemically-based life, and if that’s so, the chances are that compounds with silicon-oxygen bonds may break down in other ways but not in such a way as to become usable again by living systems. This would ultimately result in a silicon-based biosphere having all its silicon locked up with oxygen, which is how things are here.

It would be interesting to attempt to replicate the Miller-Urey experiment with silane instead of methane. This was an attempt to replicate the chemical conditions of Earth soon after formation to discover whether biochemicals found in life today would form, and it succeeded. It used water, ammonia, methane and hydrogen, and resulted in the production of such compounds as the amino acid glycine and the sugar ribose. However, although this is a fruitful exercise, it doesn’t reflect the kind of conditions likely to exist in any real situation. The interstellar medium does contain silane and several other silicon compounds, so this is not entirely unrealistic, but the concentration of silane and other silicon-based substances is much lower than their carbon-based equivalents.

A strong argument against silicon-based life could be made on the basis of the existence of organic life on this planet. Silicon is almost a thousand times more abundant that carbon, and yet life developed based on this far less widespread element. This might, though, result from other conditions being unsuitable such as the presence of water, which is however the most abundant compound in the Universe. For silicon to combine with ease in other ways, oxygen would have to be relatively scarce. On Earth, oxygen is the most abundant element in the crust, much of it combined with silicon, and I may be wrong but I find it hard to imagine a rocky planet whose situation is different enough to enable silicon to form other compounds routinely. Oxygen is the third most abundant element in the Universe as a whole, and is more than a dozen times as common as silicon. It isn’t necessarily that silicon-based life is impossible so much that other factors make it unlikely ever to happen on its own, without intervention.

That said, there might be a reason for manufacturing silicon-based microbes, for example, to reclaim plastic waste or as part of a manufacturing process. In a sense, microbes are highly complex nanotech devices, and organic life forms can only do so much because the range of conditions in which they can function is limited. The same applies to silicon-based life, but this is a potential advantage as it prevents the “grey goo scenario” of self-replicating devices eating up the planet. This brings up the issue of exotic solvents.

Although silicon biochemistry is bound to be very different to its carbon-based equivalent, what I’ve described so far is substantially similar, and as such it would require a solvent. It can’t use water unless silicon enzymes are able to catalyse in those conditions without being damaged. Silicon-based life attempting to use water is like carbon-based life attempting to use mercury as a substitute for water, which would combine with the sulphur in proteins and destroy their structure, except more severely because any silicon atom with free electrons would bind to the oxygen, liberating hydrogen incidentally, but also knackering the structure of its macromolecules. This is the big problem with silicon-based life in fact, and although I’ve suggested that entirely artificial silicon-based life forms could be used to clean up the environment, they would have to be exposed to water to do their job, which would be very harmful to them. Although glass, silica and many other silicon compounds are excellent at keeping water out without reacting, some kind of solvent would need to get in there with the molecular machinery that’s actually doing the living, i.e. the metabolism, if the biochemistry has any similarity to that of life as we know it.

One possibility here is methanol. This is the simplest alcohol, with this structure:

Somewhat ironically, the reason why this might work is probably that it has a carbon atom bound to the oxygen, which is stronger than a silicon-oxygen bond, so silicon will not pull it away from the molecule and annihilate its own structures. Methanol is found in the interstellar medium, and there’s no reason why it wouldn’t occur on planets. Its melting point is -97°C, so in an atmosphere it’s entirely possible that liquid methanol could exist on the surface of a planet, though above the melting point of water ice it would do so as a mixture with water, which would be unsuitable, so if there are worlds with methanol oceans that might be a start. However, methanol is not as abundant as water, unlike another candidate solvent, sulphuric acid. Sulphuric acid is widely distributed in our own solar system, on Venus, Mars and Io for example, and this suggests that there are whole planets out there with sulphuric acid oceans, or at least lakes. Sulphuric acid seems to be much better at supporting diverse silicon chemistry than water is.

It isn’t entirely true that silicon never forms double bonds. This occurs in silene, for example. I have to be honest here and confess that I don’t know if the existence of a double bond in silene means it can occur in any other situations. While bonds are under consideration, it’s worth looking a bit more closely at the differences between carbon and silicon chemistry. The covalent radius of a silicon atom is 117 picometres compared to carbon’s 77, but the length of the silicon-oxygen bond is 163 pm compared to carbon’s 143, from which the radii must be subtracted, leading to a shorter bond length outside the covalent radius for silicon, which makes the molecules more potentially crowded for the latter and so less diverse. There just isn’t the space around silicon atoms for there to be as much variety per atom.

That said, one thing I haven’t considered yet is the question of siloxanes. Is it possible that rather than envisaging an oxygen-free environment for silicon-based life, we should be thinking in terms of just letting it happen and seeing where that would lead us? Siloxanes include both cyclical compounds and silicon oils and rubbers, all of which have their parallels in carbon-based biochemistry. Silanols are siloxanes in a sense because they have the silicon-oxygen bond, and it’s possible to build other compounds from them. Oxidation leads to the formation of silica, so this may ultimately be an unstable situation for life to exist in, but perhaps for a short period it could.

Life as we don’t quite know it, that is, still relying on complex chemistry and solvents, has certain requirements. By definition, it needs a solvent, which in our case is water but could hypothetically be various other compounds including the aforementioned sulphuric acid and methanol, but also potentially formaldehyde, ammonia or hydrogen sulphide, which I’ll talk about in a bit. It needs enough different kinds of chemicals to perform various functions, and it needs the right balance between chemical stability and reactivity. It can’t afford to have a “doomsday pathway” where an essential and irreplaceable function causes a reaction to practically inert compounds, because this would end up locking all of the central elements up in those substances, and this appears to be what silica is in the case of silicon-based life. On the other hand, this could be useful in biotechnology to protect the environment, as it amounts to artificial organisms cleaning themselves up after their work is done.

Hence I would say that silicon-based life of this kind is possible if it was carefully designed and functioned in a highly specialised and protected environment, but it could never kick-start itself. It’s feasible that a sealed vessel in a lab could be provided with an appropriate solvent, be free of water and oxygen and be seeded with a variety of silicon-based chemicals by an intelligent life form or machine intelligence and then either spontaneously assemble into simple life forms or be purposefully manufactured as such, and there are also reasons for doing this, but there is very probably no world anywhere in the Universe where this happened on its own. In fact, if we did happen to find a planet or moon with silicon-based life on it, it would be good evidence for the existence of intelligent life somewhere.

Having said all that, there are other ways in which life could be silicon-based than simply imagining the mimicry of organic biochemistry, and perhaps all these stringent requirements just mean that biochemistry as such only really applies to our own very specific kind of life. Nowadays, classical computers are silicon-based, with doping from other elements, e.g. traces of arsenic to alter the atomic structure and allow them to function as arrays of transistors. However, this requires conditions where elemental silicon can form or be deposited, which are hard to imagine. It’s also interesting from the perspective of whether intelligence has to be alive. It’s possible to imagine some kind of crystalline process occurring on a planet where transistors or other switches grow out of inorganic materials which never fit the criteria of life but nevertheless evolve and increase their information processing capacity until they count as intelligent. This, however, is evolution and that would arguably make something alive. For instance, it would reproduce. A much more straightforward way in which intelligent machines could appear would be through what we’re doing now with our development of artificial intelligence, and many have claimed that a solution to the Fermi Paradox, for instance, is that interstellar intelligence is entirely machine-based. Considering the current trends in AI, space travel, nanotech and genetic engineering, a combination of applications of these in the long term could lead to self-replicating intelligent spacecraft who would be very much at home in interplanetary space if not interstellar, the problem there being energy sources, which could be addressed by going into a sleep mode and coasting, perhaps for centuries, to reach resources, which is far more practical for a machine designed to do that than a human, although for all we know other intelligent life forms might be absolutely fine with dormancy over long periods due to the conditions they evolved to cope with. Such entities probably wouldn’t consist of biological materials as we understand them and the usual restrictions on biochemistry assumed above wouldn’t apply. No solvent would be needed, a few inorganic compounds and elements would be sufficient and so forth.

Returning to “life as we know it” to some extent, there are several possible biochemical options which have not been mentioned yet. Prominent among these is boron. Like carbon and silicon, boron avidly forms covalent compounds though with three bonds rather than four. It forms three covalent bonds and is a metalloid, with some properties typical of metals and some of non-metals. The compounds it forms are often based on polyhedral forms, either closed or like a basket, in which atoms of other elements can be incorporated. It has at least eight different pure forms (allotropes), similar to carbon’s diamond, graphite, fullerenes and bucktubes. On a molecular level it tends to form icosahedra and there is a fullerene-like form consisting of forty atoms. It also has an extensive chemistry with an affinity for ammonia.

Hence boron chemistry can go in two directions towards complex structures with behaviour. On the one hand, it can be like conventional biochemistry, but with ammonia rather than water as a solvent, so it can have complex carbon-like chemistry. This might involve boranes, which are explosive in oxidising environments such as our own lower atmosphere but would be more stable in a reducing atmosphere, such as one mainly consisting of hydrogen. Boranes are boron hydrides, but differ in shape from hydrocarbons because they tend to form the basket shapes mentioned already, or icosahedra. It can form double bonds like carbon. Hence it’s possible to imagine boron-based life living in a hydrogen-rich atmosphere in conditions where ammonia is liquid and acting as a solvent, on a relatively cold world whose temperature is around -77°C or above, how high exactly depending on the atmospheric pressure. Such conditions are possible on the super-Earth/sub-Neptune planets which are in fact the most common of all types of planet but are not found in this Solar System, which is a puzzle, provided they are just outside the “Goldilocks Zone” for our kind of life.

On the other, there’s the possibility, which also exists for carbon, of nano-“machines” being built from the structures which pure boron forms. Hence there is perhaps another route into life which is not really biochemical. The interesting thing about boron, and it can be interesting in spite of its name, is that it kind of straddles biochemistry and nanotech in a way carbon doesn’t. With carbon, the structures of biochemistry are of course exceedingly useful and versatile, but they generally consist of polymers. Boron is able to form molecules with unusual structures which are kind of quasi-crystalline and can work both mechanically and chemically.

There is, however, a big issue with boron I haven’t mentioned yet. It’s rare. It’s less common than the next fifteen elements, up to scandium, and also the second rarest of the four lightest elements, beryllium being much more scarce due to the difficulty of its formation. Hence, whereas boron has exciting possibilities as a basis for life, like silicon it’s unlikely ever to happen without intervention. If anything, it’s more likely even than silicon to act as the basis for biochemistry, but silicon is the seventh most abundant element and boron the thirty-fourth. It’s possible that shortcomings in silicon chemistry prevent silicon-based life, but in the case of boron it could merely be its scarcity compared to carbon.

This probably exhausts the possibilities of elements as the basis for life using similar biochemistry to our own, but it doesn’t have much relevance to other possibilities for life. I’ve already mentioned plasma-based life, to which chemistry isn’t very relevant and it is possible that we’ve got a bit too hung up on chemistry as the only possibility. Another couple are associated with neutron stars. Firstly, there is the option explored by Robert L. Forward in his ‘Dragon’s Egg’ novels. Forward imagines that neutrons on the surface of such a star could combine in various ways like atoms do into molecules, and have their own equivalent to chemistry. They would however have lives millions of times faster than ours, and he also supposed that their life expectancy would be around half an hour, which is quite reasonable. There is a second suggestion concerning the interior of a neutron star which was explored by Stephen Baxter in his Xeelee series, which I haven’t read and don’t understand, and there is also the Orion’s Arm version, which may be related, of Hildemar’s Knots. These are quite difficult to understand and explain, but seem to depend on the probable fact that the interior of a neutron star is likely to be superfluid and have quantised microvortices of rotation. In order to explain this, helium II is a little closer to everyday experience.

Helium is the only baryonic matter with no solid state under pressures encountered routinely on the surface of this planet. This is a little abstract as it also has the lowest boiling point of any substance, and therefore can’t be stably surrounded by a gas under pressure since everything else is solid at that temperature. There are two common isotopes of helium, helium-4 and helium-3, and because of the way spin works, one consists of bosons and the other of fermions. Above a certain temperature, all helium behaves rather like an ordinary liquid except for being almost invisible, but below it, the helium-4 isotope becomes what’s referred to a little confusingly as helium II. At a much colder temperature, helium-3 also enters this state, which is referred to as superfluidity, and is a macroscopic quantum state. It behaves as a mixture of ordinary fluid and a fluid with no viscosity at all. It can climb vertical surfaces and it flows more easily through small holes than large ones. It conducts heat at the speed of sound, a feature also found in superconductors which means that effectively a small amount of helium II is always at the same temperature throughout. With respect to Hildermar’s Knots, the important property of superfluids is that when they’re stirred, they continue to rotate forever because they have no viscosity, and the vortex formed is quantised, and due to the peculiar nature of half-integral spin things then become really confusing. Neutron stars spin very fast and this, I think, stirs the interior superfluid neutronium into quantised vortices, each exhibiting a single quantum of angular momentum and also of magnetic flux. This results in a dense tangle of filaments. Something called the Urca Process involved in the cooling of neutron stars leads to an excess of left-handed electrons which become spin currents. The topology of these filaments changes if they touch, leading to a wave being emitted through the medium. Braids of these filaments amount to life because they can consume left-handed electrons, the braids can store information and the waves propagate signals like nerve impulses. In Orion’s Arm, Hildemar’s Knots can’t relate to the Universe outside their neutron star and regard it as an abstract mathematical problem rather than the Universe. Likewise, attempting to get one’s head round what quantised vortex filament braids in neutronium within neutron stars actually are is very like trying to solve an abstract mathematical problem. It isn’t clear to me how much of this is handwaving, but if it isn’t, it’s an interesting observation because it means that both modes of life regard the other as arcane and abstract. Also, neither can approach or exist in the other’s realm. This goes beyond “environment” because the interior of a neutron star and the kind of space compatible with atomic matter are so different that they hardly make sense to each other. Although a neutron star is only the size of a medium-sized city considered from the outside, they will distort space to some extent on the inside, and the amount of matter within them is enough to make half a million Earth-sized planets. Moreover, all of this would be happening on an absolutely minute scale.

There’s a second kind of theoretical filamentous life which may exist within less extreme stars, made of cosmic strings. Before I launch into this, I want to point out that I have my doubts about the very basis of this life form. There is an issue with magnetic monopoles, and it goes like this. We’re used to the idea of positive and negative electrical charges and the idea that one can exist without the other. There are positrons, protons, electrons and muons, all of which have isolated charges which are not paired by their opposites, although they attract each other. It might be thought that south and north magnetic poles could also exist alone, but this has never been found, and if a bar magnet is cut in half sideways it just becomes two smaller bar magnets with a north and south pole each. This seems to go on no matter how many times it’s done. Remarkably, this was discovered in the twelfth Christian century and the reason for it has never been discovered. Physics as it stands today often insists that magnetic monopoles must exist somewhere, but if they do, none have ever been detected and I personally don’t believe they exist. If they do, they would form a kind of exotic matter whose orbitals would be much smaller than those of electrons in atoms, but they would be somewhat like them nevertheless and crowd together like atoms, and consequently they would be extremely dense and yet not at all of the kind of matter which makes up superdense objects we know about such as white dwarfs and neutron stars. Because they’re so dense, it’s possible that they’re only found inside massive objects such as planets and stars. That’s the first bit.

The second bit can be explained by combing hair. I have a double crown, meaning that I can’t really have a parting. There are two whorls on my head. Most people have only one because their bodies are not covered in the kind of hair which grows, or grew, on their head, but if it was everyone would have a double crown. This is presumably the case for other species of ape, and of course for cats and dogs, to take two examples. These are known as topological defects and are thought to exist in the Universe because of the way it formed. Space only appears to be Euclidean. Two parallel lines do not in fact stay the same distance apart but will meet at a finite distance, but it appears to be Euclidean to most observers outside an immensely strong gravity well. However, space is markèdly non-Euclidean near a cosmic string because it’s a defect in space, such that a circle around such an object would have less than 360°. This peculiarity makes them very dense but their width is similar to that of a proton. They behave as one-dimensional objects, and a kilometre long stretch of a cosmic string would be more massive than Earth. This gives it an unimaginably huge density, and it may be that they are responsible for the clumping of matter seen in the Universe, where galaxies form into clusters and filaments because they have all fallen towards the strings. That said, there could also be cosmic strings whose “non-Euclideanness” is opposite, such that circles around them would have more than 360°, and these would have immensely negative mass. If these exist, it would be possible to move away from them faster than light, so they probably don’t, but that doesn’t mean the ones with psitive mass don’t either.

Both magnetic monopoles and cosmic strings are topological defects like partings and hair whorls in geometry, so they have an affinity to each other. Monopoles might appear as if threaded onto a cosmic string, and when this happens, the resultant beaded “necklace” could have something like chemistry. Neither may it have escaped your attention that this sounds once again rather like DNA, the difference being that magnetic monopoles can only be of two types, south and north. At this point it’s necessary to define the nature of life, which for the purposes of this suggestion has three characteristics. It can encode information. This is the thing which it’s difficult to understand how plasma life cells would be able to do along with the microspheres mentioned in that same post, and which for now constitutes a problem in imagining how plasma-based life is possible. Our own life solved it with DNA and RNA, initially at least. Another characteristic is that such information carriers must be able to replicate before they’re destroyed. This has an interesting dynamism with it which appeals to my Marxist brain, as it means life can only be considered as having a history from cradle to grave. The final characteristic is a surce of free energy, which considering we’re talking about life inside living stars is not exactly in short supply.

Were it as simple as magnetic monopoles lined up on a cosmic string, equilibrium would prefer north and south poles to alternate and no real information could be stored on the necklace, but each monopole could be further split into two semi-poles, making four possible semi-poles which do not necessarily annihilate each other as hey would if they were simply monopoles and their corresponding antiparticles. This makes four base-pairs which can exist on their own strings, which is remarkably similar to the structure of DNA, with four possible encoding items each of which can couple with precisely one other partner situated on a different string or strand.

This whole possibility is not intended so much to represent a real situation, although it may, as to show how different life might be to how we generally understand it. If a situation that different to carbon-based proteinaceous organic life using water as a solvent can exist, the sheer variety of possible life forms is enormous, which multiplies the possible locations suitable for life many times. The way things are here, including all these possibilities, the habitable zones for life around stars has been expanded, the types of planets or moons involved are also more varied, there are at least two possibilities on and in neutron stars and there’s a further possibility inside ordinary stars. Then there are possibly multitudinous other types of life that haven’t even been thought of. So once again, even in a Universe where there were very few Earth-like planets, many other possibilities exist and the Cosmos could once again be seen to be teeming with life. The only problem is how to recognise it.