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.

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Martian water

To have life, a planet needs water. Mars, being cold, has ice. There is a water ice-cap at the North Pole, and presumably at the South Pole. Yet there are huge valleys consistent with once having had huge flows through them. A recent scientific paper in Science (vol 348, pp218 – 221) shows evidence that Mars once had enough water to cover an area equal to that of the whole planet to a depth of 137 meters. Since Mars is now a desert, where did it go? Some would be lost to space, but a lot probably sunk into the ground, and apparently there are large areas in the northern hemisphere where underground ice sheets have been located by radar.

Having said that, there has been a recent news item of water on Mars at Gale Crater. This might be misleading. What they appear to have found is damper soil, and this has arisen because the salt calcium perchlorate sucks water from almost anywhere and dissolves, and does so at very much lower temperatures. If you mix salt (sodium chloride) with ice, it dissolves in water from the ice and takes heat from the ice, and settles as a liquid at minus 20 oC. Calcium chloride takes the temperature much lower, and apparently, so does calcium perchlorate. Yes, water can be present on Mars, even at the lower temperatures if there is something dissolved in it that lowers the freezing point enough.

Now, one of the puzzles of Mars is that there is evidence of quite significant fluid flows, in the form of great valleys carved out of the land, and which sometimes meander, but always go downhill. There should have been plenty of water, but the average temperature of Mars is currently about minus 80 oC, and back in time when these valleys formed, the sun would have been only 2/3 as bright. Unless the temperatures can be over 0 oC water freezes, so what created these valleys? Carbon dioxide as a greenhouse gas would not have sufficed, because if there were the necessary amounts available, the pressure and temperature would lead it to raining out, then as the temperature dropped with lower pressure, the carbon dioxide would frost out as a solid (dry ice). There was simply not enough heat to keep enough carbon dioxide in the atmosphere. Finally, the evidence available is that Martian temperatures never got above minus 60 oC for any significant length of time over a significant area.

The other alternative would be to dissolve something in the water to lower its freezing point. That something would not be calcium chloride or calcium perchlorate, because there simply is not enough of it around, and if there were, there would be massive deposits of lime or gypsum now. So, what could it be? When I was writing my fictional book Red Gold, which was about fraud during the colonization of Mars, I needed something unexpected to expose the fraud, and I thought that whatever caused these fluid flows could be the answer. The problem is simple: something was needed to lower the temperature of the melting point of ice by at least sixty Centigrade degrees, and not many things do that. But, there is another problem. Some of the longest fluid flows start in the southern highlands, which will be amongst the coldest parts of Mars. The reason they start there is simple in some ways: that will be where snow falls, or even where ice that has sublimed elsewhere will frost out. So, why does it melt? It cannot be something like calcium chloride because even leaving aside the point that it may not take the temperatures low enough and there was not enough of it, there most certainly was not enough in one place to keep going, and solids do not move.

My answer was ammonia. Ammonia is a gas, and hence it can get to the highlands, and furthermore, it dissolves in ice, then melts it, as long as the temperatures are at least minus eighty degrees Centigrade. Thus ammonia is one of the very few agents that could conceivably have done what was required. Given that, why is ammonia never cited by standard science? The reason is that ammonia in the air would be destroyed by solar UV, and studies have shown that ammonia would only last a matter of decades.

I argue that reasoning is wrong. On Earth, after 1.4 billion years, samples of sea water were trapped in rock at Barberton, in South Africa, and this water had almost as much ammonia in it as there was potassium. The salt levels were very high, presumably because water got boiled off when the volcanic melt solidified and sealed the water inside, and if that were the case, ammonia would have been lost too, so my estimate that ten percent of the Earth’s nitrogen remained in the form of ammonia may have been an underestimate. Why would the ammonia not be degraded? There are two reasons. The first is that most of the ammonia would be dissolved in water and not be in the air. The second is, ammonia degraded in the upper atmosphere would react with other degradation products and form a haze that would act as a sunscreen that would seriously slow down the degradation. That is the chemistry that causes the haze on Titan.

So what happened to the ammonia on Mars? My answer was, ammonia reacts with carbon dioxide to form first, ammonium carbonate, and subsequently, urea amongst other things. Such solids would dissolve in water, and in my opinion, then sink into the soil and lie below the Martian surface. This would account for why the Martian atmosphere has only about 2% nitrogen in it, and it is only 1% as thick as Earth’s atmosphere. (Nitrogen would not freeze out.) The alternative, of course, is that Mars never had any more nitrogen, in which case my argument fails because there is nothing to make the ammonia with. Does it matter? As I noted in the novel, if you want to settle Mars, yes, it would be very helpful to find a natural fertilizer resource. As to whether this happened, something carved out those valleys, and so far suggestions of what are thin and far between.

If anyone is interested, the ebook is on a Kindle countdown special, starting May 1. Besides the story, there is an appendix that outlines the first form of what would become my theory of planetary formation.