Lunar Water

Currently, if people go to the Moon, they will have to take everything they need with them. Shelter might be able to use some local materials, but almost everything else will have to come from Earth. Tools and manufactured items obviously have to be taken, but so must food, air and water. But what happens in the longer run? The expenses that will be run up like that will mean that the Moon will remain a useless lump of rock unless some alternatives are found.

A recent paper (He et al. Nature geoscience https://doi.org/10.1038/s41561-023-01159-6 ) claimed that the Changé-5 rover found water of about 1mg/g in glass beads formed by impacts. They then estimated that there were enough such glass beads across the lunar surface to get 2.7 x 10^14 kg of water. An interesting point was that the water had the D/H ratio approximately equal to solar hydrogen, and the authors proposed the water was imprinted into the beads by the solar wind. Looks like the problem is solved: the surface area of the Moon is 38 million square km, so one square kilometre will give you 7,000 t of water. If there is that much water in glass beads, and we would have at least 7 million t of such glass beads per square km, why did none of the Apollo samples bring back any of these glass beads? My guess is this is something of a gross overestimate. I have no doubt there are glass beads and they truly found water in them, but sorry, the estimate of how many there are must be wrong. The rover may have accidentally found a good deposit.

So that raises the question, is there water on the Moon? First, the information here is mixed. There is a dreadful bias to find what you expect. The original samples brought back from the Apollo missions had a water content, but the people who found it assumed it came from absorption when the samples were on Earth so they disregarded the water. Interestingly, the samples had a D/H ratio that was effectively solar, so the water could not have come from Earth. So the preconceived notion that the moon was anhydrous meant that the possibility of humans staying there for any length of time was not considered to be serious. Had it been found that there was water, maybe the Apollo program would not have been terminated and maybe the space station would not have been built as more effort would focus on the Moon. The history of space travel changed by “I know best”.

“Water” formed by solar winds is well established,  but it is formed as hydroxyl groups. With silicates, the outer surface does not properly complete its bonding, so hydrogen atoms can convert lone oxygen radicals to hydroxyls. The other half of the bond would be a radical that could react with water in the solar wind. That this probably happens is found by the “water” giving a reasonable spectroscopic signal in the evening, but is much weaker during the lunar morning. There are other samples that have  been shown to contain low levels of water. Apatites returned by Apollo had water up to 200 ppm, and some unusual volcanic glasses had water up to 46 ppm. Even more surprising is a claim that one sample of lunar soil contained nitrogen in low levels, and that nitrogen was not solar as it had enhanced levels of 15N.

So, there is water on the Moon. The TV program, “For All Humanity” had a lunar research settlement beside a crater where, deeper down the sun never penetrated. There was ice. Ridiculous? Not at all because NASA crashed a vehicle into such a region and found water of very approximately 5.6% by mass. Associated with the water was (as a % of the water) H₂S 16.5%, NH₃ 6%, SO₂ 3.2%, ethylene 3.1%, CO₂ 2.2%, methanol 1.6%, methane 0.7% (Colaprete et al. 2010 Science 330: 463-468). The water would be trapped as ice in regions where the sun does not strike, as these get extremely cold, rock being a very poor conductor of heat. It has been estimated that at latitudes greater than 80 degrees, water could be trapped in parts of craters that get no sunlight. Where did those minor materials come from? The assumption is that in this case the Moon was struck by some cometary material, and the temporary atmosphere was cold-trapped.

Water is indeed critical, but in some ways nitrogen is even more critical. Going in and out of a habitat is bound to lose air, and nitrogen is critical to dilute oxygen. It is also critical if you want to grow plants. Whether we would want to stay on the Moon for long is a matter of opinion, but at least now it may be more a possibility.

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To the Centre of the Earth

One of the interesting comments from a recent Physics World is that we do not know much about what the middle of our planet is like. Needless to say, that is hardly surprising – we cannot exactly go down there and fossick around. Not that you would want to. The centre of the Earth is about 6000 km down. About half-way down (3,000 km) we run into a zone that is believed to be molten iron. That, perforce, is hot. Then, further down, we find a solid iron core. You might wonder why it would be solid underneath the liquid? I shall come to that, but here is a small test if you are interested. Try to find an answer to that question before you get down to it.

In the meantime, how do we get any information of what is going on down there? Basically, from earthquakes. What earthquakes do is send extremely powerful shockwaves through the planet. These are effectively sound waves, although the frequency may not be in the hearing range. What we get are two wave velocities: compression and shear, and from these we can estimate the density of the materials, and isolate where there is a division between layers. That works because if we have a boundary of different composition on each side, waves will travel at different velocities through the materials. If there is a reasonably sharp boundary, the waves striking it are either transmitted or reflected, according to the velocities of the sound in each of the media, while the velocity of a sound wave is proportional to the square root of the shear modulus and inversely proportional to the density. Now, as you can see, by obtaining shear and compression velocities, we are able to sort out what is going on, again, assuming a sharp boundary. Boundaries between different phases, such as solid and liquid are usually sufficiently sharp. However, because of the number of phases, and the fact we get reflections and transmission at each boundary, there is more than a little work required to sort out what is going on from the wave patterns. To add to the problem, while the waves take multiple routes, and therefore take multiple times to get there, earthquakes are notorious for going on for some time.

Anyway, what has happened is that the physicists have worked out what these wave patterns should be like, and what we see is not quite what we expected from a nickel/iron core. Basically, the core is not quite as dense as expected. That means there must be something else there. That raises the question, what is it? It also raises the question, are the expectations realistic?

This question arises from the fact that the temperatures and pressures at the centre of the Earth convey unknown properties to materials. We can makes a good estimate of the pressure because that is the weight of the rock etc above a point and we know the mass of Earth. The temperature we can only really guess. The pressure on the surface of Earth is about 100,000 Pascals. The pressure at the centre of Earth is about 364 Gpa, or over 3.5 million times greater. If you did go there, you would be squashed. To give you an idea, the density of iron is a little over 7.87 times that of water. The density of iron at that pressure is 13.87 times that of water, or about 57% of the volume for the same mass. When iron was squeezed in a diamond anvil to a similar volume, it was found that for the Earth’s core the compressive sound velocity was 4% slower, and the shear velocity about 36% slower. They therefore concluded that the inner core had lighter elements, such as about 3% silicon and 3% sulphur.

Which raises the question, why those elements? The authors say these elements came through the growth of the inner core from the outer core. There is no real way of knowing, but for those who follow the mechanism of planetary formation outlined in my ebook “Planetary Formation and Biogenesis” other possible elements might be nitrogen and carbon. The reason lies in the problem of how the metal core separated out under the huge pressures, which slows separation greatly. My answer is that the metals separated out in the accretion disk, and the iron-cored meteorites we see now are residues of that process. The nickel-iron arrived pre-separated, and so was easier to separate out. At the same time, the temperatures were ideal for making iron nitride and iron carbide contaminants.

Now, why is the core a solid? The answer comes from how a liquid works. To be a liquid it has to flow. Heat is simply random kinetic energy, and in a liquid when a molecule strikes another, it slips past it, so there is no structure. When you cool a liquid at atmospheric pressure, the molecules form interactions that hold them in a configuration where they do not slip past each other, hence they form a crystal. However, at the extreme pressures of the Earth’s centre, the reason for a solid is quite different: they do not slip past each other because there is simply not enough room. They cannot push anything out of the way because there is nowhere for it to go.

Why is there no Disruptive Science Being Published?

One paper (Park et al. Nature 613: pp 138) that caught my attention over the post-Christmas period made the proposition that scientific papers are getting less disruptive over time, until now, in the physical sciences, there is essentially very little disruption currently. First, what do I mean by disruption? To me, this is a publication that is at cross-purposes with established thought. Thus the recent claim there is no sterile neutrino is at best barely disruptive because the existence of it was merely a “maybe” solution to another problem. So why has this happened? One answer might be we know everything so there is neither room nor need for disruption. I can’t accept that. I feel that scientists do not wish to change: they wish to keep the current supply of funds coming their way. Disruptive papers keep getting rejected because what reviewer who has spent decades on research want to let through a paper that essentially says he is wrong? Who is the peer reviewer for a disruptive paper?

Let me give a personal example. I made a few efforts to publish my theory of planetary formation in scientific journals. The standard theory is that the accretion disk dust formed planetesimals by some totally unknown mechanism, and these eventually collided to form planets. There is a small industry in running computer simulations of such collisions. My paper was usually rejected, the only stated reason being it did not have computer simulations. However, the proposition was that the growth was caused chemically and used the approximation there were no collisions. There was no evidence the reviewer read the paper past the absence of mention of simulations in the abstract. No comment about the fact here was the very first mechanism stated as to how accretion started and with a testable mathematical relationship regarding planetary spacing.

If that is bad, there is worse. The American Physical Society has published a report of a survey relating to ethics (Houle, F. H., Kirby, K. P. & Marder, M. P. Physics Today 76, 28 (2023). In a 2003 survey, 3.9% of early physicists admitted that they had been required to falsify data, or they did it anyway, to get to publication faster, to get more papers. By 2020, that number has risen to 7.3%. Now, falsifying data will only occur to get the result that fits in with standard thinking, because if it doesn’t, someone will check it.

There is an even worse problem: that of assertion. The correct data is obtained, any reasonable interpretation will say it contradicts the standard thinking, but it is reported in a way that makes it appear to comply. This will be a bit obscure for some, but I shall try to make it understandable. The paper is: Maerker, A.; Roberts, J. D. J. Am. Chem.Soc. 1966, 88, 1742-1759. At the time there was a debate whether cyclopropane could delocalize electrons. Strange effects were observed and there were two possible explanations: (1) it did delocalize electrons; (2) there were electric field effects. The difference was that both would stabilize positive charge on an adjacent centre, but the electric field effects would be opposite if the charge was opposite. So while it was known that putting a cyclopropyl ring adjacent to a cationic centre stabilized it, what happened to an anionic centre? The short answer is that most efforts to make R – (C-) – Δ, where Δ means cyclopropyl failed, whereas R – (C-) – H is easy to make. Does that look as if we are seeing stabilization? Nevertheless, if we put the cyclopropyl group on a benzylic carbon by changing R to a phenyl group φ so we have φ – (C-) – Δ an anion was just able to be made if potassium was the counter ion. Accordingly it was stated that the fact the anion was made was attributed to the stabilizing effect of cyclopropyl. No thought was given to the fact that any chemist who cannot make the benzyl anion φ – (C-) – H should be sent home in disgrace. One might at least compare like with like, but not apparently if you would get the answer you don’t want. What is even more interesting is that this rather bizarre conclusion has gone unremarked (apart from by me) since then.

This issue was once the source of strong debate, but a review came out and “settled” the issue. How? By ignoring every paper that disagreed with it, and citing the authority of “quantum mechanics”. I would not disagree that quantum mechanics is correct, but computations can be wrong. In this case, they used the same  computer programmes that “proved” the exceptional stability of polywater. Oops. As for the overlooked papers, I later wrote a review with a logic analysis. Chemistry journals do not publish logic analyses. So in my view, the reason there are no disruptive papers in the physical sciences is quite clear: nobody really wants them. Not enough to ask for them.

Finally, some examples of papers that in my opinion really should have  done better. Weihs et al. (1998) arXiv:quant-ph/9810080 v1 claimed to demonstrate clear violations of Bell’s inequality, but the analysis involved only 5% of the photons? What happened to the other 95% is not disclosed. The formation of life is critically dependent on reduced chemicals being available. A large proportion of ammonia was found in ancient seawater trapped in rocks at Barberton (de Ronde et al. Geochim.  Cosmochim. Acta 61: 4025-4042.) Thus information critical for an understanding of biogenesis was obtained, but the information was not even mentioned in the abstract or in keywords, so it is not searchable by computer. This would have disrupted the standard thinking of the ancient atmosphere, but nobody knew about it. In another paper, spectroscopy coupled with the standard theory predicted strong bathochromic shifts (to longer wavelengths) for a limited number of carbenium ions, but strong hypsochromic shifts were observed without comment (Schmitze, L. R.; Sorensen, T. S. J. Am. Chem. Soc. 1982, 104, 2600-2604.) So why was no fuss made about these things by the discoverers? Quite simply, they wanted to be in with the crowd. Be good, get papers, get funded. Don’t rock the boat! After all, nature does not care whether we understand or not.

Rocky Planet Atmospheres

Where did the rocky planets get their atmospheres from? This question is not trivial. Planets accrete by some mechanism whereby dust particles form larger objects and sooner or later these form planets. However, when they are small, they are either in a vacuum, or earlier they are in the gas that is falling into the sun and which will make the sun. If they are in a vacuum there is no gas to accrete. If they are in the gas streaming into the star they will absorb some gas more or less in proportion to what is in the gas stream, with some preference of heavier gas per unit concentration. However, that preference will not mean much because the concentration of hydrogen is so high it will swamp out most of the rest. When the rocky planet gets big enough, it will form an atmosphere from the accretion disk gas, so these two mechanisms predict either no atmosphere (accretion after the disk gas is gone) or gas that is predominantly hydrogen and helium.

When the sun ejected its accretion disk, it continued to send out a flux of high-energy UV radiation. What is expected to happen then is this would boil the hydrogen atmosphere into space, and this hydrodynamic outflow would take most of the other gases with it. None of the rocky planets in our solar system has enough gravity to hold hot hydrogen and helium for long. So any gas accreted so far is either underground or lost to space. The rocky planets start without an atmosphere, except maybe residual heavy gas that was not blown away by the strong UV. The only gases that are likely to have been so held are krypton and xenon, and they have an excess of heavy isotopes that indicate they may be such residues.

The next possibility is the gases were trapped underground and emitted volcanically after the extreme UV from the sun had stopped. Now the hydrogen and helium could leak away to space slowly and leave everything else behind. But we know that our atmosphere is not a remnant of gas from the accretion disk held by gravity or absorption because if it were, neon is about as common as nitrogen in those gases, and they would be absorbed at about the same rate and both would be held equally by gravity. If our atmosphere was delivered that way, it should contain at least 0.6 bar of neon, which is many orders of magnitude greater than what we see. Neon is a very rare gas on Earth.

Attempts to answer this question have mixed results, and tend to divide scientists into camps, wherein they defend their positions vigorously. One school of thought has the gases were forced into a magma ocean that arises from the heat of the collisions of entities about the size of Mars. I disagree with this. Should this have happened, the time taken to get the collisions going (originally estimated as 100 million years, subsequently reduced to about 30 million years with some unspecified correction to the calculations to accommodate the planet being here when the Moon-forming collision occurred) the gas would have long gone. And if the calculations were so wrong and it did happen, we are back to the neon problem.

The usual way out of this is to argue the gases came from carbonaceous chondrites, which are supposedly bits knocked off asteroids from the outer part of the asteroid belt. Such chondrites sometimes have quite reasonable amounts of water in them, as well as solids containing carbon and nitrogen. The idea is that these hit the earth, get hot, and the water oxidises the carbonaceous material to liberate carbon dioxide and nitrogen gas. Ten years ago I published the first edition of my ebook “Planetary Formation and Biogenesis”, which contained evidence that this could not be the source of the gases. The reasons were numerous and some of them complex, but one simple reason is the three rocky planets all have different proportions of the different elements. How can this happen if they came from a common source?

Now, a paper has appeared (Péron and Mukhopadhyay, Science 377: 320 – 324) that states that the krypton gas in the Chassigny meteorite, shows Mars accreted chondritic volatiles before nebular gases. I have a logic problem with this: the nebula gases were there before Mars even started forming. There was never any time that there was a Mars and the nebular gases had yet to arrive. They then found the krypton and xenon had isotope ratios that fell on a line between cosmogenic and what they assigned as trapped Martian mantle gases. There is a certain danger in this because the rock would have been exposed to cosmic rays, which lead to spallation and isotope alteration. Interestingly, the xenon data contradicts a previous report by Ott in 1948 (Geochim Cosmochim Acta 52: 1937 – 1948), who found the xenon was solar in nature. It may be that these differences can be simply explained because these are taken from a meteorite and only very small amounts of the meteorite are allowed to be taken. The samples may not be representative. Interestingly Péron and Mukhopadhyay consider the meteorite to have come from the Martian interior, based on the observation by Ott that the sample had been heated to a high temperature and was presumably of volcanic nature. The problem I see with that is that Ott came to the same conclusion for a number of other meteorites that have quite different isotope ratios. It is usually wrong to draw major conclusions from an outlier result. Anyway, based on the argument that Ott thought this meteorite was igneous, this latest paper concludes that its rare gases came from the interior of Mars, and hence show the volatiles did not come from carbonaceous chondrites.

In my opinion, the conclusion is valid, but not for the right reasons. What annoys me is the example that a previous researcher thought the sample might have been volcanic rock is assume to have come from deep in the interior now, while the previous results that do not fit the proposition are put to one side. I think that small differences from two tiny samples show you should not draw conclusions. I know there are funding pressures on scientists to publish papers, but surely everything in their work and previous work they quote should be self-consistent or reasons be found for discrepancies.

The First Atmosphere

Ι have now published the second edition of my ebook “Planetary Formation and Biogenesis”. It has just under 1290 references, each about a different aspect of the issue, although there is almost certainly a little double counting because references follow chapters, and there will be some scientific papers that are of sufficient importance to be mentioned in two chapters. Nevertheless, there is plenty of material there. The reason for a second edition is that there has been quite a lot of additional; information from the past decade. And, of course, no sooner did I publish than something else came out, so I am going to mention that in this post. In part this is because it exemplifies some of what I think is wrong with modern science. The paper, for those interested, is from Wilcoski et al. Planet Sci J. 3: 99. It is open access so you can read it.

First, the problem it attempts to address: the standard paradigm is that Earth’s atmosphere was initially oxidised, and comprised carbon dioxide and nitrogen. The question then is, when did this eventuate? What we know is the Earth was big enough that if still in the accretion disk it would have had an atmosphere of hydrogen and helium. If it did not accrete until after the disk was expelled, it would have no atmosphere initially, and an atmosphere had to come from some other process. The ebook shows the evidence and in my opinion it probably had the atmosphere of hydrogen. Either way, the accretion disk gets expelled, and assuming our star was the same as others, for the first few hundred million years the star gave off a lot of extremely energetic UV radiation, and that would be sufficient to effectively blow any atmosphere away. So under that scenario, for some number of hundred million years there would be no atmosphere.

There is an opposing option. Shortly after the Moon-forming event, there would be a “Great Bombardment” of massive impactors. There are various theories this would form a magma ocean and there is a huge steam atmosphere, but there is surprisingly little evidence for this, which many hold onto no matter what. The one piece of definite evidence are some zircons from the Jack Hills in Australia, and these are about 4.2 – 4.3 billion years old – the oldest of any rock we have. Some of these zircons show clear evidence that they formed under temperatures not that different from today. In particular, there was water that had oxygen isotope ratios expected of water that had come from rain.

So, let me revisit this paper. The basic concept is that the Earth was bombarded with massive asteroids and the iron core hit the magma ocean, about half of it was sent into the atmosphere (iron boils at 2861 degrees C) where it reacted with water to form hydrogen and ferrous oxide. The hydrogen reacted with nitrogen to form ammonia.

So, what is wrong with that? First, others argue that iron in the magma ocean settles to the core. That, according to them, is why we have a core. Alternatively, others argue if it comes from an asteroid, it emulsifies in the magma. Now we have the iron doing three different kind of things depending on what answer you want. It can do one of them, but not all of them. Should iron vapour get into the atmosphere, it would certainly reduce steam and make hydrogen, but then the hydrogen would not do very much, but rather would be lost to space because of the sun’s UV. The reaction of hydrogen with nitrogen only proceeds to make much ammonia when there is intense pressure. That could happen deep underground. However, in atmospheric pressure at temperatures above the boiling point of iron, ammonia would immediately dissociate and form nitrogen and hydrogen. The next thing that is wrong is that very few asteroids have an iron core. If one did, what would happen to the asteroid when it hit magma? As an experiment, throw ice into water and watch what happens before it tries to reverse its momentum and float (which an asteroid would not do). Basically, the liquid is what gets splashed away. Rock is a very poor conductor of heat, so the asteroid will sink quite deeply into the liquid and will have to melt off the silicates before the iron starts to melt, and then, being denser, it will sink to the core. On top of that it was assumed the atmosphere contained 100 bars of carbon dioxide, and two bars of nitrogen, in other words an atmosphere somewhat similar to that of Venus today. Assuming what was there to get the answer you want is, I suppose, one way of going about things, in a circular sort of way. However, with tidal heating from a very close Moon, such an atmosphere with that much water would never rain, which contradicts the zircon data. What we have is a story that contradicts the very limited physical evidence we have, which has no evidence in favour of it, and was made up to get the answer wanted so they could explain where the chemicals that formed life might have come from. Needless to say, my ebook has a much better account, and has the advantage that no observations contradict it.

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?

Unexpected Astronomical Discoveries.

This week, three unexpected astronomical discoveries. The first relates to white dwarfs. A star like our sun is argued to eventually run out of hydrogen, at which point its core collapses somewhat and it starts to burn helium, which it converts to carbon and oxygen, and gives off a lot more energy. This is a much more energetic process than burning hydrogen to helium, so although the core contracts, the star itself expands and becomes a red giant. When it runs out of that, it has two choices. If it is big enough, the core contracts further and it burns carbon and oxygen, rather rapidly, and we get a supernova. If it does not have enough mass, it tends to shed its outer matter and the rest collapses to a white dwarf, which glows mainly due to residual heat. It is extremely dense, and if it had the mass of the sun, it would have a volume roughly that of Earth.

Because it does not run fusion reactions, it cannot generate heat, so it will gradually cool, getting dimmer and dimmer, until eventually it becomes a black dwarf. It gets old and it dies. Or at least that was the theory up until very recently. Notice anything wrong with what I have written above?

The key is “runs out”. The problem is that all these fusion reactions occur in the core, but what is going on outside. It takes light formed in the core about 100,000 years to get to the surface. Strictly speaking, that is calculated because nobody has gone to the core of a star to measure it, but the point is made. It takes that long because it keeps running into atoms on the way out, getting absorbed and re-emitted. But if light runs into that many obstacles getting out, why do you think all the hydrogen would work its way to the core? Hydrogen is light, and it would prefer to stay right where it is. So even when a star goes supernova, there is still hydrogen in it. Similarly, when a red giant sheds outer matter and collapses, it does not necessarily shed all its hydrogen.

The relevance? The Hubble space telescope has made another discovery, namely that it has found white dwarfs burning hydrogen on their surfaces. A slightly different version of “forever young”. They need not run out at all because interstellar space, and even intergalactic space, still has vast masses of hydrogen that, while thinly dispersed, can still be gravitationally acquired. The surface of the dwarf, having such mass and so little size, will have an intense gravity to make up for the lack of exterior pressure. It would be interesting to know if they could determine the mechanism of the fusion. I would suspect it mainly involves the CNO cycle. What happens here is that protons (hydrogen nuclei) in sequence enter a nucleus that starts out as ordinary carbon 12 to make the element with one additional proton, which then decays to produce a gamma photon, and sometimes a positron and a neutrino until it gets to nitrogen 15 (having been in oxygen 15) after which if it absorbs a proton it spits out helium 4 and returns to carbon 12. The gamma spectrum (if it is there) should give us a clue.

The second is the discovery of a new Atira asteroid, which orbits the sun every 115 days and has a semi-major axis of 0.46 A.U. The only known object in the solar system with a smaller semimajor axis is Mercury, which orbits the sun in 89 days. Another peculiarity of its orbit is that it can only be seen when it is away from the line of the sun, and as it happens, these times are very difficult to see it from the Northern Hemisphere. It would be interesting to know its composition. Standard theory has it that all the asteroids we see have been dislodged from the asteroid belt, because the planets would have cleaned out any such bodies that were there from the time of the accretion disk. And, of course, we can show that many asteroids were so dislodged, but many does not mean all. The question then is, how reliable is that proposed cleanout? I suspect, not very. The idea is that numerous collisions would give the asteroids an eccentricity that would lead them to eventually collide with a planet, so the fact they are there means they have to be resupplied, and the asteroid belt is the only source. However, I see no reason why some could not have avoided this fate. In my ebook “Planetary Formation and Biogenesis” I argue that the two possibilities would have clear compositional differences, hence my interest. Of course, getting compositional information is easier said than done.

The third “discovery” is awkward. Two posts ago I wrote how the question of the nature of dark energy might not be a question because it may not exist. Well, no sooner had I posted, than someone came up with a claim for a second type of dark energy. The problem is, if the standard model is correct, the Universe should be expanding 5 – 10% faster than it appears to be doing. (Now, some would say that indicates the standard model is not quite right, but that is apparently not an option when we can add in a new type of “dark energy”.) This only applied for the first 300 million years or so, and if true, the Universe has suddenly got younger. While it is usually thought to be 13.8 billion years old, this model has it at 12.4 billion years old. So while the model has “invented” a new dark energy, it has also lost 1.4 billion years in age. I tend to be suspicious of this, especially when even the proposers are not confident of their findings. I shall try to keep you posted.

Where to Look for Alien Life?

One intriguing question is what is the probability of life elsewhere in the Universe? In my ebook, “Planetary Formation and Biogenesis” I argue that if you need the sort of chemistry I outline to form the appropriate precursors, then to get the appropriate planet in the habitable zone your best bet is to have a G-type or heavy K-type star. Our sun is a G-type. While that eliminates most stars such as red dwarfs, there are still plenty of possible candidates and on that criterion alone the universe should be full of life, albeit possibly well spread out, and there may be other issues. Thus, of the close stars to Earth, Alpha Centauri has two of the right stars, but being a double star, we don’t know whether it might have spat out its planets when it was getting rid of giants, as the two stars come as close as Saturn is to our sun. Epsilon Eridani and Tau Ceti are K-type, but it is not known whether the first has rocky planets, and further it is only about 900 million years old so any life would be extremely primitive. Tau Ceti has claims to about 8 planets, but only four have been confirmed, and for two of these, one gets about 1.7 times Earth’s light (Venus get about 1.9 times as much) while the other gets about 29%. They are also “super Earths”. Interestingly, if you apply the relationship I had in my ebook, the planet that gets the most light, is the more likely to be similar geologically to Earth (apart from its size) and is far more likely than Venus to have accreted plenty of water, so just maybe it is possible.

So where do we look for suitable planets? Very specifically how probable are rocky planets? One approach to address this came from Nibauer et al. (Astrophysical Journal, 906: 116, 2021). What they did was to look at the element concentration of stars and picked on 5 elements for which he had data. He then focused on the so-called refractory elements, i.e., those that make rocks, and by means of statistics he separated the stars into two groups: the “regular” stars, which have the proportion of refractory elements expected from the nebular clouds, or a “depleted” category, where the concentrations are less than expected. Our sun is in the “depleted” category, and oddly enough, only between 10 – 30% are “regular”. The concept here is the stars are depleted because these elements have been taken away to make rocky planets. Of course, there may be questions about the actual analysis of the data and the model, but if the data holds up, this might be indicative that rocky planets can form, at least around single stars. 

One of the puzzles of planetary formation is exemplified by Tau Ceti. The planet is actually rather short of the heavy elements that make up planets, yet it has so many planets that are so much bigger than Earth. How can this be? My answer in my ebook is that there are three stages of the accretion disk: the first when the star is busily accreting and there are huge inflows of matter; the second a transition when supply of matter declines, and a third period when stellar accretion slows by about four orders of magnitude. At the end of this third period, the star creates huge solar winds that clear out the accretion disk of gas and dust. However, in this third stage, planets continue accreting. This third stage can last from less than 1 million years to up to maybe forty. So, planets starting the same way will end up in a variety of sizes depending on how long the star takes to remove accretable material. The evidence is that our sun spat out its accretion disk very early, so we have smaller than average planets.

So, would the regular stars not have planets? No. If they formed giants, there would be no real selective depletion of specific elements, and a general depletion would register as the star not having as many in the first place. The amount of elements heavier than helium is called metallicity by astronomers, and this can vary by a factor of at least 40, and probably more. There may even be some first-generation stars out there with no heavy elements. It would be possible for a star to have giant planets but show no significant depletion of refractory elements. So while Nibauer’s analysis is interesting, and even encouraging, it does not really eliminate more than a minority of the stars. If you are on a voyage of discovery, it remains something of a guess which stars are of particular interest.