Molecular Oxygen in a Comet

There is a pressure, these days, on scientists to be productive. That is fair enough – you don’t want them slacking off in a corner, but a problem arises when this leads to the publication of papers: there are so many of them that nobody can keep up with even a small fraction of them. Worse, many of them do not seem to say much. Up to a point, this has an odd benefit: if you leave a lot unclear, all your associates can publish away and cite you, which has this effect of making you seem more important because funders like to count citations. In short, with obvious exceptions, the less you advance the science, the more important you seem at second level funding. I am going to pick, maybe unfairly, on one paper from Nature Astronomy (https://www.nature.com/articles/s41550-022-01614-1) as an illustration.

One of the most unexpected findings in the coma of comet 67P/Churyumov-Gerasimenko was “a large amount” of molecular oxygen. Something to breathe! Potential space pilots should not get excited; “a large amount” is only large with respect to what they expected, which was none. At the time, this was a surprise to astronomers because molecular oxygen is rather reactive and it is difficult to see why it would be present. Now there is a “breakthrough”: it has been concluded there is not that much oxygen in the comet at all, but this oxygen came from a separate small reservoir. The “clue” came from the molecular oxygen being associated with molecular water when emitted from a warm site. As it got cooler, any oxygen was associated with carbon dioxide or carbon monoxide. Now, you may well wonder what sort of clue that is? My question is, given there is oxygen there, what would you expect? The comet is half water, so when the surface gets warm, it sublimes. When cooler, only gases at that lower temperature get emitted. What is the puzzle?

However, the authors of the paper came to a different conclusion. They decided that there had to be a deep reservoir of oxygen within the comet, and a second reservoir close to the surface that is made of porous frozen water. According to them, oxygen in the core works its way to the surface and gets trapped in the second reservoir. Note that this is an additional proposition to the obvious one that oxygen was trapped in ice near the surface. We knew there was gas trapped in ice that was released with heat, so why postulate multiple reservoirs, other than to get a paper published?

So, where did this oxygen come from? There are two possibilities. The first is it was accreted with the gas from the disk when the comet formed. This is somewhat difficult to accept. Ordinary chemistry suggests that if oxygen molecules were present in the interstellar dust cloud it should react with hydrogen and form water. Maybe that conclusion is somehow wrong, but we can find out. We can estimate the probability by observing the numerous dust clouds from which stars accrete. As far as I am aware, nobody has ever found rich amounts of molecular oxygen in them. The usual practice when you are proposing something unusual is you find some sort of supporting evidence. Seemingly, not this time.

The second possibility is that we know how molecular oxygen could be formed at the surface. High energy photons and solar wind smash water molecules in ice to form hydrogen and hydroxyl radicals. The hydrogen escapes to space but the hydroxyl radicals unite to form hydrogen peroxide or other peroxides or superoxides, which can work their way into the ice. There are a number of other solids that catalyse the degradation of peroxides and superoxides back to oxygen, which would be trapped in the ice, but released when the ice sublimed. So, from the chemist’s point of view there is a fairly ordinary explanation why oxygen might be formed and gather near the surface. From my point of view, Occam’s Razor should apply: you use the simplest explanation unless there is good evidence. I do not see any evidence about the interior of the comet.

Does it matter? From my point of view when someone with some sort of authority/standing says something like this, there is the danger that the next paper will say “X established that . . “  and it becomes almost a gospel. This is especially so when the assertion cannot be easily challenged with evidence as you cannot get inside that comet. Which gives the perverse realization that you need strong evidence to challenge an assertion, but maybe no evidence at all to assert it in the first place. Weird?

Ebook Discount

For a short  time my ebook Spoliation is price reduced on Amazon. Unlike Kindle Countdowns, this discount applies world-wide, and I am experimenting to see how effective this strategy is.

The Board, is a ruthless, shadowy organization with limitless funds that employs space piracy and terrorism. A disgraced Captain Jonas Stryker is acting as an asteroid miner, and when The Board resorts to using a weaponised asteroid to get its way, only Stryker can divert the asteroid. The Board is determined to have Stryker killed, officially he is wanted for murder, so Stryker must expose and destroy this organization to have any future.

A story of greed, corruption and honour, combining science and visionary speculation that goes from the high frontier to outback Australia. The background also gives a scientific perspective on asteroid mining.

Warp Drives

“Warp drives” originated in the science fiction shows “Star Trek” in the 1960s, but in 1994, the Mexican Miguel Alcubierre published a paper arguing that under certain conditions exceeding light speed was not forbidden by Einstein’s General Relativity. Alcubierre reached his solution by assuming it was possible, then working backwards to see what was required while rejecting those awkward points that arose. The concept is that the ship sits in a bubble, and spacetime in front of the ship is contracted, while that behind the ship is expanded. In terms of geometry, that means the distance to your destination has got smaller, while the distance from where you started gets longer, i.e. you moved relative to the starting point and the destination. One of the oddities of being in such a bubble is you would not sense you are moving. There would be no accelerating forces because technically you are not moving; it is the space around you that is moving. Captain Kirk on the enterprise is not squashed to a film by the acceleration! Since then there have been a number of proposals. General relativity is a gold mine for academics wanting to publish papers because it is so difficult mathematically.

There is one small drawback to these proposals: you need negative energy. Now we run into definitions, and before you point out the gravitational field has negative energy it is generated by positive mass, and it contracts the distance between you and target, i.e. you fall towards it. If you like, that can be at the front of your drive. The real problem is at the other end – you need the repulsive field that sends you further from where you started, and if you think gravitationally, the opposite field, presumably generated from negative mass.

One objection often heard to negative energy is if quantum field theory were correct, the vacuum would collapse to negative energy, which would lead to the Universe collapsing on itself. My view is, not necessarily. The negative potential energy of the gravitational field causes mass to collapse onto itself, and while we do get black holes in accord with this, the Universe is actually expanding. Since quantum field theory assumes a vacuum energy density, calculations of the relativistic gravitational field arising from this are in error by ten multiplied by itself 120 times, so just maybe it is not a good guideline here. It predicts the Universe has long since collapsed, but here we are.

The only repulsive stuff we think might be there is dark energy, but we have no idea how to lay hands on it, let alone package it, or even if it exists. However, all may not be lost. I recently saw an article in Physics World that stated that a physicist, Erik Lentz, had claimed there was no need for negative energy. The concept is that energy could be capable of arranging the structure of space-time as a soliton. (A soliton is a wave packet that travels more like a bubble, it does not disperse or spread out, but otherwise behaves like a wave.) There is a minor problem. You may have heard that the biggest problem with rockets is the mass of fuel they have to carry before you get started. Well, don’t book a space flight yet. As Lentz has calculated it, a 100 m radius spacecraft would require the energy equivalent to hundreds of times the mass of Jupiter.

There will be other problems. It is one thing to have opposite energy densities on different sides of your bubble. You still have to convert those to motion and go exactly in the direction you wish. If you cannot steer as you go, or worse, you don’t even know for sure exactly where you are and the target is, is there a point? Finally, in my science fiction novels I have steered away from warp drives. The only times my characters went interstellar distances I limited myself to a little under light speed. Some say that lacks imagination, but stop and think. You set out to do something, but suppose where you are going will have aged 300 years before you get there. Come back, and your then associates have been dead for 600 years. That raises some very awkward problems that make a story different from the usual “space westerns”.

What Happens Inside Ice Giants?

Uranus and Neptune are a bit weird, although in fairness that may be because we don’t really know much about them. Our information is restricted to what we can see in telescopes (not a lot) and the Voyager fly-bys, which, of course, also devoted a lot of attention to the Moons, since a lot of effort was devoted to images. The planets are rather large featureless balls of gas and cloud and you can only do so much on a “zoom-past”. One of the odd things is the magnetic fields. On Earth, the magnetic field axis corresponds with the axis of rotation, more or less, but not so much there. Earth’s magnetic field is believed to be due to a molten iron core, but that could not occur there. That probably needs explaining. The iron in the dust that is accreted to form planets is a fine powder; the particles are in the micron size. The Earth’s core arises because the iron formed lumps, melted, and flowed to the core because it is denser. In my ebook “Planetary Formation and Biogenesis” I argue that the iron actually formed lumps in the accretion disk. While the star was accreting, the region around where Earth is reached something like 1600 degrees C, above the melting point of iron, so it formed globs. We see the residues of that in the iron-cored meteorites that sometimes fall to Earth. However, Mars does not appear to have an iron core. Within that model, the explanation is simple. While on Earth the large lumps of iron flowed towards the centre, on Mars, since the disk temperature falls off with distance from the star, at 1.5 AU the large lumps did not form. As a consequence, the fine iron particles could not move through the highly viscous silicates, and instead reacted with water and oxidised, or, if you prefer, rusted.

If the lumps that formed for Earth could not form at Mars because it was too far away from the star, the situation was worse for Uranus. As with Mars, the iron would be accreted as a fine dust and as the ice giants started to warm up from gravitational collapse, the iron, once it got to about 500 degrees Centigrade, would rapidly react with the water and oxidise to form iron oxides and hydrogen. Why did that not happen in the accretion disk? Maybe it did, and maybe at Mars it was always accreted as iron oxides, but by the time it got to where Earth is, there would be at least ten thousand times more hydrogen than iron, and hot hydrogen reduces iron oxide to iron. Anyway, Uranus and Neptune will not have an iron core, so what could generate the magnetic fields? Basically, you need moving electric charge. The planets are moving (rotating) so where does the charge come from?

The answer recently proposed is superionic ice. You will think that ice melts at 0 degrees Centigrade, and yes, it does, but only at atmospheric pressure. Increase the pressure and it melts at a lower temperature, which is how you make snowballs. But ice is weird. You may think ice is ice, but that is not exactly correct. There appear to be about twenty ices possible from water, although there are controversial aspects because high pressure work is very difficult and while you get information, it is not always clear about what it refers to. You may think that irrespective of that, ice will be liquid at the centre of these planets because it will be too hot for a solid. Maybe.

In a recent publication (Nature Physics, 17, 1233-1238 November 2021) authors studied ice in a diamond anvil cell at pressures up to 150 GPa (which is about 1.5 million times greater than our atmospheric pressure) and about 6,500 degrees K (near enough to Centigrade at this temperature). They interpret their observations as there being superionic ice there. The use of “about” is because there will be uncertainty due to the laser heating, and the relatively short times up there. (Recall diamond will also melt.)

A superionic ice is proposed wherein because of the pressure, the hydrogen nuclei can move about the lattice of oxygen atoms, and they are the cause of the electrical conduction. These conditions are what are expected deep in the interior but not at the centre of these two planets. There will presumably be zones where there is an equilibrium between the ice and liquid, and convection of the liquid coupled with the rotation will generate the movement of charge necessary to make the magnetism. At least, that is one theory. It may or may not be correct.

Your Water Came from Where?

One interesting question when considering why Earth has life is from where did we get our water? This is important because essentially it is the difference between Earth and Venus. Both are rocky planets of about the same size. They each have similar amounts of carbon dioxide, with Venus having about 50% more than Earth, and four times the amount of nitrogen, but Venus is extremely short of water. If we are interested in knowing about whether there is life on other planets elsewhere in the cosmos, we need to know about this water issue. The reason Venus is hell and Earth is not is not that Venus is closer to the Sun (although that would make Venus warmer than Earth) but rather it has no water. What happened on Earth is that the water dissolved the CO2 to make carbonic acid, which in turn weathered rocks to make the huge deposits of lime, dolomite, etc that we have on the planet, and to make the bicarbonates in the sea.

One of the more interesting scientific papers has just appeared in Nature Astronomy (https://doi.org/10.1038/s41550-021-01487-w) although the reason I find it interesting may not meet with the approval of the authors. What the authors did was to examine a grain of the dust retrieved from the asteroid Itokawa by the Japanese Space agency and “found it had water on its surface”. Note it had not evaporated after millions of years in a vacuum. The water is produced, so they say, by space weathering. What happens is that the sun sends out bursts of solar wind which contains high velocity protons. Space dust is made of silicates, which involve silica bound to four oxygen atoms in a tetrahedron, and each oxygen atom is bound to something else. Suppose, for sake of argument, the something else is a magnesium atom. A high energy hydrogen nucleus (a proton) strikes it and makes SiOH and, say Mg+, with the Mg ion and the silicon atom remaining bound to whatever else they were bound to. It is fairly standard chemistry that 2SiOH → SiOSi plus H2O, so we have made water. Maybe, because the difference between SiOH on a microscopic sample of dust and dust plus water is rather small, except, of course, Si-OH is chemically bound to and is part of the rock, and rock does not evaporate. However, the alleged “clincher”: the ratio of deuterium to hydrogen on this dust grain was the same as Earth’s water.

Earth’s water has about 5 times more deuterium than solar hydrogen, Venus about a hundred times. The enhancement arises because if anything is to break the bond in H-O-D, the hydrogen is slightly more probable to go because the deuterium has a slightly stronger bond to the oxygen. Also, being slightly heavier, H-O-D is slightly less likely to get to the top of the atmosphere.

So, a light bulb moment: Earth’s water came from space dust. They calculate that this would produce twenty litres of water for every cubic meter of rock. This dust is wet! If that dust rained down on Earth it would deliver a lot of water. The authors suggest about half the water here came that way, while the rest came from carbonaceous chondrites, which have the same D/H ratio.

So, notice anything? There are two problems when forming a theory. First, the theory should account for everything of relevance. In practice this might be a little much, but there should be no obvious problems. Second, the theory should have no obvious inconsistencies. First, let us look at the “everything”. If the dust rained down on the Earth, why did not the same amount rain down on Venus? There is a slight weakness in this argument because if it did, maybe the water was largely destroyed by the sunlight. If that happened a high D/H ratio would result, and that is found on Venus. However, if you accept that, why did Earth’s water not also have its D/H ratio increased? The simplest explanation would be that it did, but not to extent of Venus because Earth had more water to dilute it. Why did the dust not rain down on the Moon? If the answer is the dust had been blown away by the time the Moon was formed, that makes sense, except now we are asking the water to be delivered at the time of accretion, and the evidence on Mars was that water was not there until about 500 million years later. If it arrived before the disk dust was lost, then the strongest supply of water would come closest to the star, and by the time we got to Earth, it would be screened by inner dust. Venus would be the wettest and it isn’t.

Now the inconsistencies. The strongest flux of solar wind at this distance would be what bombards the Moon, and while the dust was only here for a few million years, the Moon has been there for 4.5 billion years. Plenty of time to get wet. Except it has not. The surface of the dust on the Moon shows this reaction, and there are signs of water on the Moon, especially in the more polar regions, and the average Moon rock has got some water. But the problem is these solar winds only hit the surface. Thus the top layer or so of atoms might react, but nothing inside that layer. We can see those SiOH bonds with infrared spectroscopy, but the Moon, while it has some such molecules, it cannot be described as wet. My view is this is another one of those publications where people have got carried away, more intent on getting a paper that gets cited for their CV than actually stopping and thinking about a problem.

Interstellar Travel Opportunities.

As you may have heard, stars move. The only reason we cannot see this is because they are so far away, and it takes so long to make a difference. Currently, the closest star to us is Proxima Centauri, which is part of the Alpha Centauri grouping. It is 4.2 light years away, and if you think that is attractive for an interstellar voyage, just wait a bit. In 28,700 years it will be a whole light year closer. That is a clear saving in travelling time, especially if you do not travel close to light speed.

However, there have been closer encounters. Sholz’s star, which is a binary; a squib of a red dwarf plus a brown dwarf, came within 0.82 light years 78,000 years ago. Our stone age ancestors would probably have been unaware of it, because it is so dim that even when that close it was still a hundred times too dim to be seen by the naked eye. There is one possible exception to that: occasionally red dwarfs periodically emit extremely bright flares, so maybe they would see a star appear from nowhere, then gradually disappear. Such an event might go down in their stories, particularly if something dramatic happened. There is one further possible downside for our ancestors: although it is unclear whether such a squib of a star was big enough, it might have exerted a gravitational effect on the Oort cloud, thus generating a flux of comets coming inwards. That might have been the dramatic event.

That star was too small to do anything to disrupt our solar system, but it is possible that much closer encounters in other solar systems could cause all sorts of chaos, including stealing a planet, or having one stolen. They could certainly disrupt a solar system, and it is possible that some of the so-called star-burning giants were formed in the expected places and were dislodged inwards by such a star. That happens when the dislodged entity has a very elliptical orbit that takes it closer to the star where tidal effects with the star circularise it. That did not happen in our solar system. Of course, it does not take a passing star to do that; if the planets get too big and too close their gravity can do it.

It is possible that a modestly close encounter with a star did have an effect on the outer Kuiper Belt, where objects like Eris seem to be obvious Kuiper Belt Objects, but they are rather far out and have very elliptical orbits. It would be expected that would arise from one or more significant gravitational interactions.

The question then is, if a star passed closely should people take advantage and colonise the new system? Alternatively, would life forms there have the same idea if they were technically advanced? Since if you had the technology to do this, presumably you would also have the technology to know what was there. It is not as if you do not get warning. For example, if you are around in 1.4 million years, Gliese 710 will pass within 10,000 AU of the sun, well within the so-called Oort Cloud. Gliese 710 is about 60% the mass of the sun, which means its gravity could really stir up the comets in the Oort cloud, and our star will do exactly the same for the corresponding cloud of comets in their system. In a really close encounter it is not within the bounds of possibility that planetary bodies could be exchanged. If they were, the exchange would almost certainly lead to a very elliptical orbit, and probably at a great distance. You may have heard of the possibility of a “Planet 9” that is at a considerable distance but with an elliptical orbit has caused highly elliptical orbits in some trans Neptunian objects. Either the planet, if it exists at all, or the elliptical nature of the orbits of bodies like Sedna, could well have arisen from a previous close stellar encounter.

As far as I know, we have not detected planets around this star. That does not mean there are not any because if we do not lie on the equatorial plane of that star we would not see much from eclipsing observations (and remember Kepler only looks at a very small section of the sky, and Gliese 710 is not in the original area examined) and at that distance, any astronomer with our technology there would not see us. Which raises the question, if there were planets there, would we want to swap systems? If you accept the mechanism of how planets form in my ebook “Planetary Formation and Biogenesis”, and if the rates of accretion, after adjusting for stellar mass for both were the same, then any rocky planet in the habitable zone is likely to be the Mars equivalent. It would be much warmer and it may well be much bigger than our Mars, but it would not have plate tectonics because its composition would not permit eclogite to form, which is necessary for pull subduction. With that knowledge, would you go?

Food on Mars

Settlers on Mars will have needs, but the most obvious ones are breathing and eating, and both of these are likely to involve plants. Anyone thinking of going to Mars should think about these, and if you look at science fiction the answers vary. Most simply assume everything is taken care of, which is fair enough for a story. Then there is the occasional story with slightly more detail. Andy Weir’s “The Martian” is simple. He grows potatoes. Living on such a diet would be a little spartan, but his hero had no option, being essentially a Robinson Crusoe without a Man Friday. The oxygen seemed to be a given. The potatoes were grown in what seemed to be a pressurised plastic tent and to get water, he catalytically decomposed hydrazine to make hydrogen and then he burnt that. A plastic tent would not work. The UV radiation would first make the tent opaque so the necessary light would not get in very well, then the plastic would degrade. As for making water, burning hydrazine as it was is sufficient, but better still, would they not put their base where there was ice?

I also have a novel (“Red Gold”) where a settlement tries to get started. Its premise is there is a main settlement with fusion reactors and hence have the energy to make anything, but the main hero is “off on his own” and has to make do with less, but can bring things from the main settlement. He builds giant “glass houses” made with layers of zinc-rich glass that shield the inside from UV radiation. Stellar plasma ejections are diverted by a superconducting magnet at the L1 position between Mars and the sun (proposed years before NASA suggested it) and the hero lives in a cave. That would work well for everything except cosmic radiation, but is that going to be that bad? Initially everyone lives on hydroponically grown microalgae, but the domes permit ordinary crops. The plants grow in treated soil, but as another option a roof is put over a minor crater and water provided (with solar heating from space) in which macroalgae grow and marine microalgae, as well as fish and other species, like prawns. The atmosphere is nitrogen, separated from the Martian atmosphere, and some carbon dioxide, and the plants make oxygen. (There would have to be some oxygen to get started, but plants on Earth grew without oxygen initially.)

Since then there have been other quite dramatic proposals from more official sources that assume a lot of automation to begin with. One of the proposals involves constructing huge greenhouses by covering a crater or valley. (Hey, I suggested that!) but the roof is flat and made of plastic, the plastic being made from polyethylene 2,5-furandicarboxylate, a polyester made from carbohydrates grown by the plants. This is used as a bonding agent to make a concrete from Martian rock. (In my novel, I explained why a cement is very necessary, but there are limited uses.) The big greenhouse model has some limitations. In this, the roof is flat, and in essentially two layers, and in between are vertical stacks of algae growing in water. The extra value here is that water filters out the effect of cosmic rays, although you need several meters of it. Now we have a problem. The idea is that underneath this there is a huge habitat, and for every cubic meter of water, we have one tonne mass, and on Mars, about 0.4 tonne of force on the lower flat deck. If this bottom deck is the opaque concrete, then something bound by plastic adhesion will slip. (Our concrete on bridges is only inorganic, and the binding is chemical, not physical, and further there is steel reinforcing.) Below this there would need to be many weight-bearing pillars. And there would need to be light generation between the decks (to get the algae to grow) and down below. Nuclear power would make this easy. Food can be grown as algae in between decks, or in the ground down below.

As I see it, construction of this would take quite an effort and a huge amount of materials. The concept is the plants could be grown to make the cement to make the habitat, but hold on, where are the initial plants going to grow, and who/what does all the chemical processing? The plan is to have that in place from robots before anyone gets there but I think that is greatly overambitious. In “Red Gold” I had the glass made from regolith processed with the fusion energy. The advantage of glass over this new suggestion is weight; even on Mars with its lower gravity millions of tonnes remains a serious weight. The first people there will have to live somewhat more simply.

Another plan that I have seen involves finding a frozen lake in a crater, and excavating an “under-ice” habitat. No shortage of water, or screening from cosmic rays, but a problem as I see it is said ice will melt from the heat, erode the bottom of the sheet, and eventually it will collapse. Undesirable, that is.

All of these “official” options use artificial lighting. Assuming a nuclear reactor, that is not a problem in itself, although it would be for the settlement under the ice because heat control would be a problem. However, there is more to getting light than generating energy. What gives off the light, and what happens when its lifetime expires? Do you have to have a huge number of spares? Can they be made on Mars?

There is also the problem with heat. In my novel I solved this with mirrors in space focussing more sunlight on selected spots, and of course this provides light to help plants grow, but if you are going to heat from fission power a whole lot more electrical equipment is needed. Many more things to go wrong, and when it could take two years to get a replacement delivered, complicated is what you do not want. It is not going to be that easy.

A Discovery on Mars

Our space programs now seem to be focusing in the increasingly low concentrations or more obscure events, as if this will tell us something special. Recall earlier there was the supposed finding of phosphine in the Venusian atmosphere. Nothing like stirring up controversy because this was taken as a sign of life. As an aside, I wonder how many people actually have ever noticed phosphine anywhere? I have made it in the lab, but that hardly counts. It is not a very common material, and the signal in the Venusian atmosphere was almost certainly due to sulphur dioxide. That in itself is interesting when you ask how would that get there? The answer is surprisingly simple: sulphuric acid is known to be there, and it is denser, and might form a fog or even rain, but as it falls it hits the hotter regions near the surface and pyrolysis to form sulphur dioxide, oxygen and water. These rise, the oxygen reacts with sulphur dioxide to make sulphur trioxide (probably helped by solar radiation), which in turn reacts with water to form sulphuric acid, which in turn is why the acid stays in the atmosphere. Things that have a stable level on a planet often have a cycle.

In February this year, as reported in Physics World, a Russian space probe detected hydrogen chloride in the atmosphere of Mars after a dust storm occurred. This was done with a spectrometer that looked at sunlight as it passed through the atmosphere, and materials such as hydrogen chloride would be picked up as a darkened line at the frequency for the bond vibration in the infrared part of the spectrum. The single line, while broadened due to rotational options, would be fairly conclusive. I found the article to be interesting for all sorts of reasons, one of which was for stating the obvious. Thus it stated that dust density was amplified in the atmosphere during a global dust storm. Who would have guessed that? 

Then with no further explanation, the hydrogen chloride could be generated by water vapour interacting with the dust grains. Really? As a chemist my guess would be that the dust had wet salt on it. UV radiation and atmospheric water vapour would oxidise that, to make at first sodium hypochlorite, like domestic bleach and then hydrogen.  From the general acidity we would then get hydrogen chloride and probably sodium carbonate dust. They were then puzzled as to how the hydrogen chloride disappeared. The obvious answer is that hydrogen chloride would strongly attract water, which would form hydrochloric acid, and that would react with any oxide or carbonate in the dust to make chloride salts. If that sounds circular, yes it is, but there is a net degradation of water; oxygen or oxides would be formed, and hydrogen would be lost to space. The loss would not be very great, of course, because we are talking about parts per billion in a highly rarefied upper atmosphere and only during a dust storm.

Hydrogen chloride would also be emitted during volcanic eruptions, but that is probably able to be eliminated here because Mars no longer has volcanic eruptions. Fumarole emissions would be too wet to get to the upper atmosphere, and if they occurred, and there is no evidence they still do, any hydrochloric acid would be expected to react with oxides, such as the iron oxide that makes Mars look red, rather quickly.  So the unfortunate effect is that the space program is running up against the law of diminishing returns. We are getting more and more information that involves ever-decreasing levels of importance. Rutherford once claimed that physics was the only science – the rest was stamp collecting.  Well, he can turn in his grave because to me this is rather expensive stamp collecting.

Living Near Ceres

Some will have heard of Gerard O’Neill’s book, “The High Frontier”. If not, see https://en.wikipedia.org/wiki/The_High_Frontier:_Human_Colonies_in_Space. The idea was to throw material up from the surface of the Moon to make giant cylinders that would get artificial gravity from rotation, and people could live their lives in the interior with energy being obtained in part by solar energy. The concept was partly employed in the TV series “Babylon 5”, but the original concept was to have open farmland as well. Looks like science fiction, you say, and in fairness I have included such a proposition in a science fiction novel I am currently writing, However, I have also read a scientific paper on this topic (arXiv:2011.07487v3) which appears to have been posted on the 14th January, 2021. The concept is to put such a space settlement using material obtained from the asteroid Ceres, and orbiting near Ceres.

The proposal is ambitious, if nothing else. The idea is to build a number of habitats, and to ensure such habitats are not too big but they stay together they are tethered to a megasatellite, which in turn will grow and new settlements are built. The habitats spin in such a way to attain a “gravity” of 1 g, and are attached to their tethers by magnetic bearings that have no physical contact between faces, and hence never wear. A system of travel between habitats proceeds along the tethers. Rockets would be unsustainable because the molecules they throw out to space would be lost forever.

The habitats would have a radius of 1 km, a length of 10 km, and have a population of 56,700, with 2,000 square meters per person, just under 45% of which would be urban. Slightly more scary would be the fact it has to rotate every 1.06 minutes. The total mass per person would be just under 10,000 t, requiring an energy to produce it of 1 MJ/kg, or about 10 GJ.

The design aims to produce an environment for the settlers that has Earth-like radiation shielding, gravity, and atmosphere. It will have day/night on a 24 hr cycle with 130 W/m^2 insolation, similar to southern Germany, and a population density of 500/km^2, similar to the Netherlands. There would be fields, parks, and forests, no adverse weather, no natural disasters and ultimately it could have a greater living area than Earth. It will be long-term sustainable. To achieve that, animals, birds and insects will be present, i.e.  a proper ecosystem. Ultimately it could provide more living area than Earth. As can be seen, that is ambitious. The radiation shielding involves 7600 kg/m^2, of which 20% is water and the rest silicate regolith. The rural spaces have a 1.5 m depth of soil, which is illuminated by the sunlight. The sunlight is collected and delivered from mirrors into light guides. Ceres is 2.77 times as far as Earth from the sun, which means the sunlight is only about 13% as strong as at Earth, so over eight times the mirror collecting are is required for every unit area to be illuminated to get equivalent energy. 

The reason cited for proposing this to be at Ceres is that Ceres has nitrogen. Actually, there are other carbonaceous asteroids, and one that is at least 100 km in size could be suitable. Because Ceres’ gravity is 0.029 times that of Earth, a space elevator could be feasible to bring material cheaply from the dwarf planet, while a settlement 100,000 km from the surface would be expected to have a stable orbit.

In principle, there could be any number of these habitats, all linked together. You could have more people living there than on Earth. Of course there are some issues with the calculation. The tethering of habitats, and of giving the habitats sufficient strength requires about 5% of the total mass in the form of steel. Where does the iron come from? The asteroids have plenty of iron, but the form is important. How will it be refined? If it is on the form of olivine or pyroxene, then with difficulty. Vesta apparently has an iron core, but Vesta is not close, and most of the time, because it has a different orbital period, it is very far away.But the real question is, would you want to live in such a place? How much would you pay for the privilege? The cost of all this was not estimated, but it would be enormous so most people could not afford it. In my opinion, cost alone is sufficient that this idea will not see the light of day.

Asteroid Mining

One thing you see often in the media is the concept that perhaps in the future we can solve our resources problem by mining asteroids. Hopefully, that is fine for science fiction, and I use that word “hopefully” because my next piece of science fiction, currently in the editing mode, includes collecting asteroids for minerals extraction. However, what is the reality?

We know we have a resource problem. An unfortunately large and growing number of elements are becoming scarcer and harder to obtain. As a consequence, ores are getting less concentrated, and so much material has to be thrown away. As an example, the earliest use of copper at around 7,000 BC used native copper. All the people had to do was take a piece and hammer it into some desirable shape. Some time later someone found that if something like malachite was accidentally in a fireplace, it got reduced to copper, and metallurgy was founded. Malachite is 57.7% copper, while if you were lucky enough to find cuprite you got a yield of almost 89% copper. Now the average yield of copper from a copper ore is 0.6% and falling. The rest is usually useless silicates. So, you may think, if we have worked through all the easily available stuff here, nobody has worked through the asteroids. There we could get “the good stuff”.

At this point it is worth contemplating what an ore is and where it came from? All the elements heavier than lithium were made in supernovae or through collisions of neutron stars. Either way, if we think of the supernova, the elements are made at an extremely high temperature, and they are flying away from the stellar core at a very high velocity. The net result is they end up as particles that make the particles in smoke look big. This “smoke” gets mixed in with gas clouds that end up making stars and planets. To get some perspective on concentrations, for every million silicon atoms you will get, on average, about 900,000 iron atoms, almost 24,000,000 oxygen atoms, 5420 chlorine atoms, 52,700 sodium atoms, 522 copper atoms, almost half a silver atom, 0.187 gold atoms, 1.34 platinum atoms and about 0.009 uranium atoms.

So what happens depends on whether the elements react in the accretion disk, so that molecules form. For example, all the sodium atoms will either form a chloride or a hydroxide, but the gold atoms will by and large not react. About half the iron atoms form an oxide or stay as the element, and the oxides will end up as silicates (basalt). What happens next depends on how the objects accrete. That is not agreed. Most scientists say they simply don’t know. I believe the bodies are accreted through chemistry. If the former, we have to assume the elements end up as a mix that have those elements in proportion, except for those that make gases. If the latter, then some will be more concentrated than others.

On earth, elements are concentrated into ores by geochemistry. The heat and water processes some elements, and heat and volcanism concentrates others. Thus gold is concentrated by it dissolving in supercritical water, together with silica, which is why you often find gold in quartz veins. The relevance to asteroids is that processing does not happen in most because they are not big enough to generate the required heat. The relevance now is that the elements you want will either be bound up with silicates, or be scattered randomly through the bulk. To get the metals out, you have to get rid of the silicates, and if you look at the figures, the copper content is actually less than in our ores on earth. Now look at the mining wastes on Earth, and ask yourself what would you do with that in space? (There is an answer – build space stations with rocky shells.)

So why do we think of mining asteroids. One reason comes from asteroid Psyche. One scientific paper once claimed asteroid had a density as high as 7.6 g/cm cubed. That would clearly be worth mining, because the iron would also dissolve nickel, cobalt, platinum, gold, etc. You will various news items that wax on about how this asteroid alone would solve our problems and make everyon extremely rich. However, other papers have published values as low as 1.4 g/cm cubed, and the average value is about 3.5 g/cm cubed (which is what it would be if it were solid basalt). 

Why the differences? Basically because density depends on the mass (determined by gravitational interactions) and volume.  The uncertainty in the volume, thanks to observational uncertainty due to the asteroid being so far away and the fact it is not round, can give an error of up to 50%. The mass requires very accurate measurements when near something else and again huge errors are possible.

So the question then is, if someone wants to get metals out of asteroids, how will they do it? If the elements are there as oxides or sulphides, what do you do about that? On Earth you heat with coal and air, followed by coal. You cannot do that in space. On Earth, minerals can be concentrated by various means that use liquids, such as froth flotation, but you cannot do that easily in space because first liquids like water are scarce, and second, if you have them, unless they are totally enclosed they boil off into space. Flotation requires “gravity”, which requires a centrifuge. Possible, but very expensive,If you were building a giant space station, yes, asteroids would be valuable because the cost of getting components from Earth is huge, but we still need technology to refine them. Otherwise the cost of getting the materials to Earth would be horrifying. Be careful if you see an investment offering.