Volatiles on Rocky Planets

If we accept the mechanism I posted before is how the rocky planets formed, we still do not have the chemicals for life. So far, all we have is water and rocks with some planets having an iron core. The mechanism means that until the planet gets gravitationally big enough to attract gas it only accretes solids, together with the water that bonded to the silicates. There re two issues: how the carbon and nitrogen arrived, and if these arrived as solids, which is the only available mechanism, what happened next?

In the outer parts of the solar system the carbon occurs as carbon monoxide, methanol, some carbon dioxide, and “carbon”, which essentially many forms but looks like tar, is partially graphite, and there are even mini diamonds. There are also polyaromatic hydrocarbons, and even alkanes, and some other miscellaneous organic chemicals. Nitrogen occurs as nitrogen gas, ammonia, and some cyanide. As this comes closer to the star, and in the region of the carbonaceous chondrites, it starts getting hot enough for some of this to condense and react on the silicates, which is why these have the aminoacids, etc. However, as you get closer to the star, it gets too hot and seemingly the inner asteroids are mainly just silicates. At this point, the carbon is largely converted to carbon monoxide, and the nitrogenous compounds to nitrogen. However, on some metal oxides or metals, carbon forms carbides, nitrogen nitrides, and some other materials, such as cyanamides are also formed. These are solids, and accordingly these too will be accreted with the dust and be incorporated within the planet.

As the interior of the planet gets hotter, the water gets released from the silicates and they lose their amorphous structure and become rocks. The water reacts with these chemicals and to a first approximation initially produces carbon monoxide, methane and ammonia. Carbon monoxide reacts with water on certain metals and silicates to make hydrocarbons, formaldehyde, which in turn condenses to other aldehydes (on the path to making sugars) ammonia (on the path to make aminoacids) and so on. The chemistry is fairly involved, but basically given the initial mix, temperature and pressure, both in ready supply below the Earth’s surface, what we need for life emerges and will make its way to the surface. Assuming this mechanism is correct, then provided everything is present in an adequate mix, then life should evolve. That leaves open the question, how broad is the “right mix” zone?

Before considering that, it is obvious this mechanism relies on the temperature being correct on at least two times during the planetary evolution. Initially it has to get hot enough to make the cements, and the nitrides and carbides. Superficially, that applies to all rocky planets, but maybe not for the nitrides. The problem here is Mars has very little nitrogen, so either it has gone somewhere, or it was never there. If Mars had ammonia, since it dissolves in ice down to minus 80 degrees C, ammonia on Mars would solve the problem of how could water flow there when it is so cold. However, if that is the case, the nitrogen has to be in some solid form buried below the surface. In my opinion, it was carried there as urea dissolved in water, which is why I would love to see some deep digging there.

The second requirement is that later the temperature has to be cool enough that water can set the cements. The problem with Venus is argued that it was hotter and it only just managed to absorb some water, but not enough. One counter to that is that the hydrogen on Venus has an extremely high deuterium content. The usual explanation for this is that if water gets to the top of the atmosphere, it may be hit with UV which may knock off a hydrogen atom, which is lost to space, and solar wind may take the whole molecule, however water with deuterium is less likely to get there because the heavier molecules are enhanced in the lower atmosphere, or the oceans. If this were true, for Venus to have the deuterium levels it must have started with a huge amount of water, and the mechanism above would be wrong. An embarrassing problem is where is the oxygen from that massive amount of water.

However, the proposed mechanism also predicts a very large deuterium enhancement. The carbon and nitrogen in the atmosphere and in living things has to be liberated from rocks by reaction with water, and what happens is as the water transfers hydrogen to either carbon or nitrogen it also leaves a hydroxyl attached to any metal. Two hydroxyls liberate water and leave an oxide. At this point we recall that chemical bond to deuterium is stronger than that to hydrogen, the reason being that although in theory the two are identical from the electromagnetic interactions, quantum mechanics requires there to be a zero point energy, and somewhat oversimplifying, the amount of such energy is inversely proportional to the square root of the mass of the light atom. Since deuterium is twice the mass of hydrogen, the zero point energy is less, and being less, its bond is stronger. That means there is a preference for the hydrogen to be the one that transfers, and the deuterium eventually turns up in the water. This preferential retaining of deuterium is called the chemical isotope effect. The resultant gases, methane and ammonia as examples, break down with UV radiation and make molecular nitrogen and carbon dioxide, with the hydrogen going to space. The net result of this is the rocky planet’s hydrogen gradually becomes richer in deuterium.

The effects of the two mechanisms are different. For Venus, the first one requires huge oceans; the second one little more than enough water to liberate the gases. If we look at the rocky planets, Earth should have a modest deuterium enhancement with both mechanisms because we know it has retained a very large amount of water. Mars is more tricky, because it started with less water under the proposed accretion of water mechanism, and it has less gravity and we know that all gases there, including carbon dioxide and nitrogen have enhanced heavier isotopes. That its deuterium is enhanced is simply expected from the other enhancements. Venus has about half as much CO2 again as Earth, and three times the amount of nitrogen, little water, and a very high deuterium enhancement. In my mechanism, Venus never had much water in the first place because it was too hot. Most of what it had was used up forming the atmosphere, and then providing the oxygen for the CO2. There was never much on the surface. To start with Venus was only a bit warmer than Earth, but as the CO2 began to build, whereas on Earth much of this would be dissolved in the ocean, where it would react with calcium silicate and also begin weathering the rocks that were more susceptible to weathering, such as dunite and peridotite. (I have discussed this previously: https://wordpress.com/post/ianmillerblog.wordpress.com/833 ), on Venus there were no oceans, and liquid water is needed to form these carbonates.

So, where will life be found? The answer is around any star where rocky planets formed with the two favourable temperature profiles, and ended up in the habitable zone. If more details as found in my ebook “Planetary Formation and Biogenesis” are correct, then this is most likely to occur around a G type star, like our sun, or a heavy K type star. The star also has to be one of the few that ejects it accretion disk remains early. Accordingly life should be fairly well spaced out, which may be why we have yet to run into other life forms.

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From Whence Star-burning Planets?

This series started out with the objective of showing how life could have started, and some may be wondering why I have spent so much time talking about the cold giant planets. The answer is simple. To find the answer to a scientific problem we seldom go directly to it. The reason is that when you go directly to what you are trying to explain you will get an explanation, however for any given observation there will be many possible explanations. The real explanation will also explain every connected phenomenon, whereas the false explanations will only explain some. The ones that are seemingly not directed at the specific question you are trying to answer will nevertheless put constraints on what the eventual answer must include. I am trying to make things easier in the understanding department by considering a number of associated things. So, one more post before getting on to rocky planets.

In the previous two posts, I have outlined how I believe planets form, and why the outer parts of our solar system look like they do. An immediate objection might be, most other systems do not look like ours. Why not? One reason is I have outlined so far how the giants form, but these giants are a considerable distance from the star. We actually have rather little information about planets in other systems at these distances. However, some systems have giants very close to the star, with orbits (years) that take days and we do not. How can that be?

It becomes immediately obvious that planets cannot accrete from solids colliding that close to the star because the accretion disk get to over 10,000 degrees C that close, and there are no solids at those temperatures. The possibilities are that either there is some mechanism that so far has not been considered, which raises the question, why did it not operate here, or that the giants started somewhere else and moved there. Neither are very attractive, but the fact these star-burning giants only occur near a few stars suggests that there is no special mechanism. Physical laws are supposedly general, and it is hard to see why these rare exceptions occur. Further, we can see how they might move.

There is one immediate observation that suggests our solar system is expected to be different from many others and that is, if we look again at LkCa 15b, that planet is three times further from the star than Jupiter is from our star, which means the gas and dust there would have more than three times less concentrated, and collisions between dust over nine times rarer, yet it is five times bigger. That star is only 2 – 3 My old, and is about the same size as our star. So the question is, why did Jupiter stop growing so much earlier when it is in a more favourable spot through having denser gas? The obvious answer is Jupiter ran out of gas to accrete much sooner, and it would do that through the loss of the accretion disk. Stars blow away their accretion disks some time between 1 and 30 My after the star essentially finishes accreting. The inevitable conclusion is that our star blew out its disk of gases in the earliest part of the range, hence all the planets in our system will be, on average, somewhat smaller than their counterparts around most other stars of comparable size. Planets around small stars may also be small simply because the system ran out of material.

Given that giants keep growing as long as gas keeps being supplied, we might expect many bigger planets throughout the Universe. There is one system, around the star HR 8799 which has four giants arrayed in a similar pattern to ours, albeit the distances are proportionately scaled up and the four planets are between five and nine times bigger than Jupiter. The main reason we know about them is because they are further from the star and so much larger, hence we an see them. It is also because we do not observe then from reflected light. They are very young planets, and are yellow-white hot from gravitational accretion energy. Thus we can see how planets can get very big: they just have to keep growing, and there are planets that are up to 18 times bigger than Jupiter. If they were bigger, we would probably call them brown dwarfs, i.e. failed stars.

There are some planets that have highly elliptical orbits, so how did that situation arise? As planets grow, they get gravitationally stronger, and if they keep growing, eventually they start tugging on other planets. If they can keep this up, the orbits get more and more elliptical until eventually they start orbiting very close to each other. They do not need to collide, but if they are big enough and come close enough they exchange energy, in which case one gets thrown outwards, possibly completely out of its solar system, and one gets thrown inwards, usually with a highly elliptical orbit. There are a number of systems where planets have elliptical orbits, and it may be that most do, and if they do, they will exchange energy gravitationally with anything else they come close to. This may lead to a sort of gravitational billiards, where the system gets progressively smaller, and of course rocky planets, being smaller are more likely to get thrown out of the system, or to the outer regions, or into the star.

Planets being thrown into the star may seem excessive, nevertheless in the last week it was announced that a relatively new star, RW Aur A, over the preceding year had a 30 fold increase in the amount of iron in its spectrum. The spectrum of a star comes from whatever is on its surface, so the assumption is that something containing a lot of iron, which would be something the size of a reasonably sized asteroid at least, fell into the star. That means something else knocked it out of its orbit, and usually that means the something else was big.

If the orbit is sufficiently elliptical to bring it very close to the star one of two things happen. The first is it has its orbit circularized close to the star by tidal interactions, and you get one of the so-called star-burners, where they can orbit their star in days, and their temperatures are hideously hot. Since their orbit is prograde, they continue to orbit, and now tidal interactions with the star will actually slowly push the planet further from the star, in the same way our moon is getting further from us. The alternative is that the orbit can flip, and become retrograde. The same thing happens as with the prograde planets, except that now tidal interactions lead to the planet slowly falling into the star.

The relevance of all this is to the question, how common is life in the Universe? If we want a rocky planet in a circular orbit in the habitable zone, then we can eliminate all systems with giants on highly elliptical orbits, or in systems with star burners. However, there is a further possibility that is not advantageous to life. Suppose there are rocky planets formed but the star has yet to elimiinate its accretion disk. The rocky planet will also keep growing and in principle could also become a giant. This could be the reason why some systems have Neptune-sized planets or “superEarths” in the habitable zone. They probably do not have life, so now we have to limit the number of possible star systems to those that eliminate their accretion disk very early. That probably elimimates about 90% of them. Life on a planet like ours might be rarer than some like to think.

The Formation of the Giant Planets

Before I can discuss how we got the elements required for life delivered to Earth, it is necessary to work out how the planets formed, and why we have what we have. While the giant planets are almost certainly not going to have life, at least not as we would recognise it, they are important because what we have actually gives some important clues as to how planets form, and hence how common life will be, and why so many exoplanetary systems are so different from ours. The standard theory says a core accreted, then when it got sufficiently big, which calculations have at about 10 to 12 times the Earth mass it starts accreting gas in substantial amounts and it grows very slowly, the problem restricting growth being how it can compress its volume and get rid of the heat so generated. After a number of million years, its mass gets big enough, and it accretes everything that comes into range. Apart from the rather slow time the calculations give, that general description is almost certainly essentially correct. The reason we believe the core has to get to about 10 – 12 Earth masses before disk gases get accreted in serious amounts is because the evidence is the Neptune and Uranus have about 2 Earth masses of hydrogen and helium. So far, reasonably good. The fact that there is evidence the calculations are wrong is not damning; the fact that if the mechanism is not properly understood in close detail then the calculations will inevitably be wrong. The original calculations had these stages taking about 10 My to get to a planet the size of Jupiter. The very first calculations had it taking about a billion years to get to Neptune, but that obviously cannot be right because the disk gases had long gone before that. The real problem is how to get to the cores.

The standard theory says they started by the accretion of a distribution of planetesimals that were formed by the accretion of dust, and therefore were distributed according to the dust concentrations through the disk. There are two problems with this for me. First, we see these disks, and we see them because their dust scatters light. Some such disks are 30 My old and still dusty, so the dust itself is not rapidly accreting, altough often there are bands where there seems to be little dust. The second problem is that there is no recognized mechanism by which the dust can accrete and stick together strongly enough not to be disrupted by any other dustball that collides with it. Mathematics indicate that such dustballs, if they reach about 2 cm size, erode from gas motion relative to them.

So, how did the cores form? I think we have evidence from the fact their systems all have different compositions. The theory I outlined in my ebook Planetary Formation and Biogenesis goes like this. The dust that comes from deep space has a lot of very fluffy ice around it, and this has many pores. Within those pores, and around the ice, are the ices of other volatiles. (Such compound ices have been made in the lab, and their behaviour verified.) As the ices come in, the more volatile ones start subliming away at temperatures a little above their melting point, and hydrogen has even been maintained as an ice enclosed in water ice pores up to a little under 15 degrees K, which is well above its boiling point. So, as the ices come in and the disk gets gradually hotter, the ices selectively boil away. The relevant temperatures are: neon (~25 K); nitrogen and carbon monoxide (~65 K); argon and methane (~ 85); ammonia and methanol (~170 K); water (273 K).

What I suggest happened is the same mechanism that forms snowballs started planetary accretion. When snow is squeezed at a temperature a little below its triple point, the pressure causes localised melt fusion, and the particles stick together. In this case we have several ices entrained in the ice/dust, and I suggest the same happens for each ice. This has consequences. The temperature profile in these disks is observed to be where the temperature T is proportional to r^-0.75, r the distance from the star, with a significant variation, which is expected because the faster the gas comes in, or the warmer it was to start with, the further out a specific temperature will be found, while the denser the gas flow, the greater the temperature gradient. Now, because Jupiter is the biggest planet, and water ice is the most common single material, assume (like everyone else) that Jupiter is more or less where the water ice so fuses. If we assume the average disk temperature profile (actually r^-0.82 is better for what follows for our solar system) then the remaining giants are quite close to where they are supposed to be. So the mechanism is that ices come together, they hit, the collisional energy melts an ice in the impact zone such that they rapidly refreeze, and the particles stick together. To predict where the planets should be I put Jupiter at 5.2 A.U. as a water-ice core sets the constant of proportionality. The next ice is ammonia/methanol/water, which could melt between 164 – 195 oK, which suggests that Saturn should be between 7.8 – 9.6 A.U. Saturn has a semimajor axis of 9.5 A.U. The next ice out is methane/argon, with melting between 84 – 90 oK. The calculated position of Uranus is between 20-21.7 A.U., while the observed position is 19.2 A.U. The next ice, carbon monoxide/nitrogen melts between 63 – 68 oK, which predicts Neptune to be between 28.1 – 30.7 A.U., and Neptune has a semimajor axis of 30 A.U. Note that as they form, we excpect some movement through gravitational interactions and the effects of the gas.

This means the Jovian system is both nitrogen and carbon deficient, apart from Jupiter itself which accreted gas from the disk, and the very tenuous atmosphere of Europa is reported to actually have more sodium in it than nitrogen. Sorry, but no life under the ice at Europa because there is nothing much with which to have organic chemistry. The reason for the lack of atmosphere is the satellites have nothing in them that could form a gas at those temperatures. The major component is hydroxyl, from the photochemiclo deomposition of water, but this is extremely reactive and does not build up.

The Saturnian system has water, plus methanol and ammonia. The ammonia has been seen at Enceladus, and its decay product during UV radiation, nitrogen, is the main gas of Titan. The methane there will come from reactions of methanol and rocks. The Uranian system has methane and argon. Unfortunately the satellites are too small to have atmospheres, and Neptune’s satellites are similar, as while Triton has nitrogen volcanoes, it is probably a captured Kuiper Belt object, as it orbits Neptune the wrong way. However the atmosphere of Neptune has more nitrogen than expected from the accretion disk, whereas Uranus does not. More specific details are in the ebook, but in my opinion, the above describes reasonably well how these systems formed, and why they have the chemical composition we see. The Kuiper belt objects are the same as the core of Neptune, and are essentially a “tail” of the accretion process.

Finally, the perceptive will notice the possibility of two further zones of accretion. Further out, there will be a zone where neon trapped in ice might accrete, and even further out, because hydrogen can be trapped in ice even up to about 15 K, a hydrogen accretion zone where the liquid hydrogen dissolves neon, which then refreezes. The latter is not impossible. There are exoplanets a few hundred A.U. from the star, or, say, over ten times further than Neptune. On the other hand, there is a further mechanism that could form them, namely collapse of the disk, which presumably starts the star. So I should be able to predict where this planet 9 is? That is not so easy because the temperature of the disk follows the above relationship only approximately, and when we get down to these low temperatures, any deviation, including the initial temperature of the gas (which in the above relation is taken as zero, but it isn’t) suddenly becomes important. My published estimate for a neon-based planet is at a hundred A.U., with a possible minus 30 and a plus fifty A.U. Not exactly helpful. If I knew thie initial temperature, and the rate of heat loss from the disk by radiation at those distances I could be far more precise.

Was there an Initial Atmosphere from Accretion?

One of the problems with modern science is that once a paradigm has been selected, a layer of “authorities” is set up, and unless the scientist adopts the paradigm, little notice is taken of him or her. This is where conferences become important, because there is an audience that is more or less required to listen. The problem then for the person who has a different view is to show why that view is important enough to be considered. The barrier is rightly high. A new theory MUST do something the old one did not do, and it must not be contradicted by known facts. As I said, a high barrier.

In the previous post, I argued that the chemicals required for life did not come from carbonaceous chondrites or comets, and that is against standard thought. Part of the reason this view is held is that the gases had to come from somewhere, so from where? There are two obvious possible answers. The first is the gases were accreted with the planet as an atmosphere. In this hypothesis, the Earth formed while the disk gases were still there and simple gravity held them. Once the accretion disk was removed by the star, the hydrogen and helium were lost to space because Earth’s gravity was not strong enough, but other gases were retained. This possibility is usually rejected, and in this case the rejection is sound.

The first part of the proposition was almost certainly correct. Gases would have been accreted from the stellar disk, even on rocky planets, and these gases were largely hydrogen and helium. The next part is also correct. Once the disk gases were removed, that hydrogen and helium would be lost to space because Earth’s gravity was not strong enough to hold it. However, the question then is, how was it lost? As it happens, insufficient gravity was not the primary cause, and the loss was much faster than simply seeping off into space. Early in the life of a new star there are vicious solar winds and extreme UV radiation. It is generally accepted that such radiation would boil off the hydrogen and helium, and these would be lost so quickly that the other gases would be removed by hydrodynamic drag, and only some of the very heavier gases, such as krypton and xenon could remain. There is evidence to support this proposal, in that for krypton and xenon higher levels of heavier isotopes are observed. This would happen if most of these gases were removed from the top of the atmosphere, and since the lighter isotopes would preferentially find their way there, they would be removed preferentially. Since this is not observed for neon or argon isotopes, the argument is that all neon and argon in the atmosphere was lost this way, and if so, all nitrogen and carbon oxides, together with all water in the atmosphere would be lost. Basically, apart from the amount of krypton and xenon currently in the atmosphere, there would be no other gases. The standard theory of planetary formation has it that the Earth was a ball of magma, and if so, all water on the surface would be in the gas phase, so for quite some time Earth would be a dry lump of rock with an atmosphere that had a pressure that would be so low only the best vacuum pumps today could match it.

There could be the objection that maybe the star was not that active and we did retain some gases. After all, we weren’t around to check. Can you see why not? I’ll give the reason shortly. However, if we accept that the gases could not have come from the accretion disk, the other alternative is they came from below the ground, i.e. they were emitted by volacanic activity. How does that stand up?

One possibility might be that gases, including water, were adsorbed on the dust, then subsequently emitted by volcanoes. You might protest that if the Earth was a magma ocean, all that water would be immediately ejected from the silicates as a gas, but it turns out that while water is insoluble in silica at surface pressures, at pressures of 5000 atmospheres, granitic magma can dissolve up to 10% water at 1100 degrees C, at least according to Wikipedia. Irrespective of the accuracy of the figures, high temperature silicates under pressure most certainly dissolve water, and it probably hydrolyses the silicate structure and makes it far less viscous. It has been estimated that the water remaining in the mantle is 100 times greater than the current oceans so there is no problem in expecting that the oceans were initially emitted by volcanic activity. As an aside, deep in the mantle the pressures are far greater than 5000 atmospheres. This water is also likely to be very important for another reason, namely reducing the viscosity and lowering the magma density. This assists pull subduction, where the dry, or drier, basalt from the surface is denser than the other material around it and hence descends into the mantle. If the water were not there, we would not have plate tectonics, and if there were no plate tectonics, there would be no recycling of carbon dioxide, so eventually all the carbon dioxide on the surface would be converted to lime and there would be nothing for plants to use. End of life!

However, we know that our atmospheric gases were not primarily adsorbed as dust. How do we know that? In the accretion disk the number of nitrogen atoms is roughly the same as the number of neon atoms, and their heats of adsorption on dust are roughly the same. The only plausible physical means of separating them in the accretion disk is selective sublimation from ice, but ice simply could not survive where Earth formed. So, if our nitrogen came from the disk by simple physical means, then we would have roughly the same amount of neon in our atmosphere as nitrogen. We don’t, and the amount of neon we have is a measure of the amount of gas we have from such adsorption. Neon is present at 0.0018%, which is not very much.

So, in answer to the initial question, for a period there was effectively no atmosphere. To go any further we have to consider how the planets formed, and as some may suspect, I do not accept the standard theory for reasons that will become apparent in the next post.

Meanwhile, may I remind readers that my ebooks on Smashwords are on discount through July. Links to novels:

Puppeteer: http://www.smashwords.com/books/view/69696

‘Bot War: https://www.smashwords.com/books/view/677836

Troubles: https://www.smashwords.com/books/view/174203

Meanwhile, if you want to know scientifically about biofuels:

Biofuels: https://www.smashwords.com/books/view/454344

Origin of the Rocky Planet Water, Carbon and Nitrogen

The most basic requirement for life to start is a supply of the necessary chemicals, mainly water, reduced carbon and reduced nitrogen on a planet suitable for life. The word reduced means the elements are at least partly bound with hydrogen. Methane and ammonia are reduced, but so are hydrocarbons, and aminoacids are at least partly reduced. The standard theory of planetary formation has it (wrongly, in my opinion) that none of these are found on a rocky planet and have to come from either comets, or carbonaceous asteroids. So, why am I certain this is wrong? There are four requirements that must be met. The first is, the material delivered must be the same as the proposed source; the second is they must come in the same proportions, the third is the delivery method must leave the solar system as it is now, and the fourth is that other things that should have happened must have.

As it happens, oxygen, carbon, hydrogen and nitrogen are not the same through the solar system. Each exists in more than one isotope (different isotopes have different numbers of neutrons), and the mix of isotopes in an element varies in radial distance from the star. Thus comets from beyond Neptune have far too much deuterium compared with hydrogen. There are mechanisms by which you can enhance the D/H ratio, such as UV radiation breaking bonds involving hydrogen, and hydrogen escaping to space. The chemical bonds to deuterium tend to be several kJ/mol. stronger than bonds to hydrogen. The chemical bond strength is actually the same, but the lighter hydrogen has more zero point energy so it more easily breaks and gets lost to space. So while you can increase the deuterium to hydrogen ratio, there is no known way to decrease it by natural causes. The comets around Jupiter also have more deuterium than our water, so they cannot be the source. The chondrites have the same D/H ratio as our water, which has encouraged people to believe that is where our water came from, but the nitrogen in the chondrites has too much 15N, so it cannot be the source of our nitrogen. Further, the isotope ratios of certain heavy elements such as osmium do not match those on Earth. Interestingly, it has been argued that if the material was subducted and mixed in the mantle, it would be just possible. Given that the mantle mixes very poorly and the main sources of osmium now come from very ancient plutonic extrusions, I have doubts on that.

If we look at the proportions, if comets delivered the water or carbon, we should have five times more nitrogen, and twenty thousand times more argon. Comets from the Jupiter zone get around this excess by having no significant nitrogen or argon, and insufficient carbon. For chondrites, there should be four times as much carbon and nitrogen to account for the hydrogen and chlorine on Earth. If these volatiles did come from chondrites, Earth has to be struck by at least 10^23 kg of material (that is, ten followed by 23 zeros). Now, if we accept that these chondrites don’t have some steering system, based on area the Moon should have been struck by about 7×10^21 kg, which is approximately 9.5% of the Moon’s mass. The Moon does not subduct such material, and the moon rocks we have found have exactly the same isotope ratios as Earth. That mass of material is just not there. Further, the lunar anorthosite is magmatic in origin and hence primordial for the Moon, and would retain its original isotope ratios, which should give a set of isotopes that so not involve the late veneer, if it occurred at all.

The third problem is that we are asked to believe that there was a narrow zone in the asteroid belt that showered a deluge of asteroids onto the rocky planets, but for no good reason they did not accrete into anything there, and while this was going on, they did not disturb the asteroids that remain, nor did they disturb or collide with asteroids closer to the star, which now is most of them. The hypothesis requires a huge amount of asteroids formed in a narrow region for no good reason. Some argue the gravitational effect of Jupiter dislodged them, but the orbits of such asteroids ARE stable. Gravitational acceleration is independent of the body’s mass, and the remaining asteroids are quite untroubled. (The Equivalence Principle – all bodies fall at the same rate, other than when air resistance applies.)

Associated with this problem is there is a number of elements like tungsten that dissolve in liquid iron. The justification for this huge barrage of asteroids (called the late veneer) is that when Earth differentiated, the iron would have dissolved these elements and taken them to the core. However, they, and iron, are here, so it is argued something must have brought them later. But wait. For the isotope ratios this asteroid material has to be subducted; for them to be on the continents, they must not be subducted. We need to be self-consistent.

Finally, what should have happened? If all the volatiles came from these carbonaceous chondrites, the various planets should have the same ratio of volatiles, should they not? However, the water/carbon ratio of Earth appears to be more than 2 orders of magnitude greater than that originally on Venus, while the original water/carbon ratio of Mars is unclear, as neither are fully accounted for. The N/C ratio of Earth and Venus is 1% and 3.5% respectively. The N/C ratio of Mars is two orders of magnitude lower than 1-2%. Thus if the atmospheres came from carbonaceous chondrites:

Only the Earth is struck by large wet planetesimals,

Venus is struck by asteroidal bodies or chondrites that are rich in C and especially rich in N and are approximately 3 orders of magnitude drier than the large wet planetesimals,

Either Earth is struck by a low proportion of relatively dry asteroidal bodies or chondrites that are rich in C and especially rich in N and by the large wet planetesimals having moderate levels of C and essentially no N, or the very large wet planetesimals have moderate amounts of carbon and lower amounts of nitrogen as the dry asteroidal bodies or chondrites, and Earth is not struck by the bodies that struck Venus,

Mars is struck only infrequently by a third type of asteroidal body or chondrite that is relatively wet but is very nitrogen deficient, and this does not strike the other bodies in significant amounts,

The Moon is struck by nothing,

See why I find this hard to swallow? Of course, these elements had to come from somewhere, so where? That is for a later post. In the meantime, see why I think science has at times lost hold of its methodology? It is almost as if people are too afraid to go against the establishment.

Science Communication and the 2018 Australasian Astrobiology Meeting

Earlier this week I presented a talk at the 2018 Australasian Astrobiology Meeting, with the objective of showing where life might be found elsewhere in the Universe, and as a consequence I shall do a number of posts here to expand on what I thought about this meeting. One presentation that made me think about how to start this series actually came near the end, and the topic included why do scientists write blogs like this for the general public? I thought about this a little, and I think at least part of the answer, at least for me, is to show how science works, and how scientists think. The fact of the matter is that there are a number of topics where the gap between what scientists think and what the general public think is very large. An obvious one is climate change; the presenter came up with a figure that something like 50% of the general public don’t think that carbon dioxide is responsible for climate change while I think the figures she showed were that 98% of scientists are convinced it does. So why is there a difference, and what should be done about it?

In my opinion, there are two major ways to go wrong. The first is to simply take someone else’s word. In these days, you can find someone who will say anything. The problem then is that while it is all very well to say look at the evidence, most of the time the evidence is inaccessible, and even if you overcome that, the average person cannot make head or tail of it. Accordingly, you have to trust someone to interpret it for you. The second way to go wrong is to get swamped with information. The data can be confusing, but the key is to find critical data. This means that when making a decision as to what causes what, you put aside facts that can mean a lot of different things, and concentrate on those that have, at best, one explanation. Now the average person cannot recognize that, but they can recognize whether the “expert” recognizes it. As an example of a critical fact, back to climate change. The fact that I regard as critical is that there was a long-term series of measurements that showed the world’s oceans were receiving a net power input of 0.6 watt per square meter. That may not sound like much, but multiply it over the earth’s ocean area, and it is a rather awful lot of heat.

Another difficulty is that for any given piece of information, either there may be several interpretations for what caused it, or there may be issues assigning significance. As a specific example from the conference, try to answer the question, “Are we alone”? The answer from Seth Shostak, from SETI, is, so far, yes, at least to the extent we have no evidence to the contrary, but of course if you were looking for radio transmissions, Earth would have failed to show signs until about a hundred years ago. There were a number of other reasons given, but one of the points Seth made was a civilization at a modest distance would have to devote a few hundred MW power to send us a signal. Why would they do that? This reminds me of what I wrote in one of my SF novels. The exercise is a waste of time because everyone is listening; listening is cheap but nobody is sending, and simple economics kills the scheme.

As Seth showed, there are an awful lot of reasons why SETI is not finding anything, and that proves nothing. Absence of evidence is not evidence of absence, but merely evidence that you haven’t hit the magic button yet. Which gets me back to scientific arguments. You will hear people say science cannot prove anything. That is rubbish. The second law of thermodynamics proves conclusively that if you put your dinner on the table it won’t spontaneously drop a couple of degrees in temperature as it shoots upwards and smears itself over the ceiling.

As an example of the problems involved with conveying such information, consider what it takes to get a proof? Basically, a theory starts with a statement. There are several forms of this, but the one I prefer is you say, “If theory A is correct, and I do a set of experiments B, under conditions C, and if B and C are very large sets, then theory A will predict a set of results R. You do the experiments and collect a large set of observations O. Now, if there is no element of O that is not an element of R, then your theory is plausible. If the sets are large enough, they are very plausible, but you still have to be careful you have an adequate range of conditions. Thus Newtonian mechanics are correct within a useful range of conditions, but expand that enough and you need either relativity or quantum mechanics. You can, however, prove a theory if you replace “if” in the above with “if and only if”.

Of course, that could be said more simply. You could say a theory is plausible if every time you use it, what you see complies with your theory’s predictions, and you can prove a theory if you can show there is no alternative, although that is usually very difficult. So why do scientists not write in the simpler form? The answer is precision. The example I used above is general so it can be reduced to a simpler form, but sometimes the statements only apply under very special circumstances, and now the qualifiers can make for very turgid prose. The takeaway message now is, while a scientist likes to write in a way that is more precise, if you want to have notice taken, you have to be somewhat less formal. What do you think? Is that right?

Back to the conference, in the case of SETI. Seth will not be proven wrong, ever, because the hypothesis that there are civilizations out there but they are not broadcasting to us in a way we can detect cannot be faulted. So for the next few weeks I shall look more at what I gathered from this conference.

What do Organic Compounds Found on Mars Mean?

Last week, NASA announced that organic compounds had been found on Mars. The question then is, what does this mean? First, organic compounds are essentially chemicals formed that involve carbon, which means Mars has carbon besides the carbon dioxide in the atmosphere. The name “organic” comes from the fact that such compounds found by early chemists, with the exception of a very few such as carbon dioxide, came from organisms, hence there is the question, do these materials indicate that Mars had life? The short answer is, the issue remains unresolved. One argument is that if there were no organic compounds on Mars, it obviously did not have life. That it has taken so long to find organic compounds does not say anything about the probability, though, because the surface of Mars is strongly oxidizing, and had any been there, they would have been turned into carbon dioxide. The atmosphere already has a lot of that. The reason none has been found, therefore, is because most of the rovers have not been able to dig very deeply.

I shall try to summarise the results that were reported [Eigenbrode et al., Science 360, 1096–1101 (2018)]. One important point is that the volatiles analysed were obtained by pyrolysing the mudstone the rover dug up, so what was detected may not be the same that was in the rock. The first compounds were identified as aliphatic hydrocarbons, from C1 (methane) to C5, and these were stated to be typical of that obtained from Kerogen or coal on Earth. One problem I had with these data was there were odd-numbered masses, BUT they all indicated that the cause was a fractured hydrocarbon, i.e. the pyrolysis had chopped that bit off something else and produced a radical.

One big problem was they could not say whether nitrogen or oxygen was present ” because mass spectra are not resolvable in EGA and other molecules share the diagnostic m/z values. ” I really don’t understand that. First, the identification of aliphatic hydrocarbons was almost certainly correct, because they form series of signals that are very recognizable to anyone who has done a bit of this work before. They stick out like an organ stop, so to speak. However, the presence of nitrogen species in any reasonable amount should be just as easily identified because while hydrocarbons, and their like with oxygen, basically give even mass signals, nitrogen, because of its valency of 3, gives odd numbered mass signals that is 1 bigger than a hydrocarbon. Now, a few of the fragmentation patterns of hydrocarbons give odd numbered mass signals, but if you cannot tell where the molecular ion is, you do not know what the mass of your molecule is. If all you have are fragmentation ions, then the instrument was somewhat poorly designed to go to Mars. With any experience, you can also tell whether you have oxygenated materials because hydrocarbons go up by adding 14 to the basic ion, and the atomic weight of oxygen is 16. If it has oxygen, it abd the fragments containing oxygen have an entirely different mass.

Of course the authors did note the presence of CO2 and CO. These could arise from the pyrolysis of carboxylic acids and ketones, but that does not mean life. Carboxylic acids would pyrolyse at about 400 – 550 degrees C and ketones a bit higher. They also found aromatic hydrocarbons, thiophenes and some other sulphur containing species. These were explained in terms of sulphur –bearing gases coming in contact, and further chemical reactions then taking place, in other words, these sulphur containing species such as hydrogen sulphide do not necessarily provide any information regarding what formed the original deposit. The sulphurization, however, was claimed to provide a preservative function by protecting against mild oxidation. If it carried out that function, it would be oxidized, and none of the observed materials were.

Unfortunately, the material is not directly associated with anything related to life. The remains of life can give rise to these sort of chemicals, as noted by our crude oil, which is basically hydrocarbon, and formed from life, but then altered by tens of millions of years change. These Martian deposits are believed to be in rocks 3.5 billion years old. However, the materials were also obtained by pyrolysis at temperatures exceeding 500 degrees C. The original molecules could have rearranged, and what we saw was the sort of compounds that organic compounds might rearrange to. Nevertheless, the absence of nitrogen is not encouraging. Nitrogen is present in all protein and nucleic acids, and there tends to be high levels of these in primitive life. Pyrolysis would be expected to produce pyrazines and pyridines, and these should be detectable. Pyrazines, having two nitrogen atoms, tend to give even numbered ions, and give the same mass as a ketone, but since neither was seen, that is irrelevant. Had there been such signals, the fragmentation patterns are quite distinctive if you have done this sort of work before.

Other possible sources of organic compounds, besides carbon, are from chondrites that have landed, and geochemically. It is hard to assess chondrites, because we do not have other information. It is possible to tell the difference between oxygen from chondrites from oxygen from other places (because of the different ratios of isotopes of mass 17 and 18 compared with 16), but they never found oxygen. The materials could be geochemical as well. The same reaction used by Germany to make synthetic petrol during WW2 can occur underground, and make hydrocarbons. So overall, while this is certainly interesting, as is often the case it raises more questions than it answers.