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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6 thoughts on “What do Organic Compounds Found on Mars Mean?

  1. Big picture remains that the rover is in what used to be a giant lake one hundred kilometers across. So Mars WAS HABITABLE. For about a billion years. Whether life evolved there is not clear: Earth is a giant churning engine of creation, with perhaps kilometer high tides at some point, every couple of hours or so… That forcefully mixed continent, sea, volcanoes, lightning, etc. If life had evolved on Mars, though, it would have transferred on Earth… thanks to impacts…
    All this is much more agitated and eventful than the old picture…
    The other drastic discovery were those towering, 100 meters high cliffs of ice on Mars. Last year. That makes Mars colonization feasible (once we have a huge energy source, like portable thermonuclear fusion…
    This sort of discoveries are more impactful than whether life evolved there. Hunting for fossils is how to solve that one… And will not be easy: 4 billion year old fossils on Earth are very controversial…
    I am a bit impact and significance obsessed… in all matters

    • The rover is in the remains of an impact crater, and I have seen maths that argue the heat of the impact would keep the water warm enough for about 30,000 years. We don’t know. I am actually giving a talk at an Astrobiology conference in just over a week, and my argument is for a variety of reasons, life has to start with RNA (It will take ten minutes of fast talking to cover why) which requires reduced nitrogen (things like ammonium cyanide and cyanoacetylene) but an interesting problem is ribose. Ribose is needed because it alone permits the phosphate ester that links the polymer, but how do you make ribose? In any ordinary pentose synthesis, all you get are xylose and arabinose, and they don’t work. However, there are reports you get ribose if the water has dissolved silica. That suggests life started near fumaroles, but the question I don’t know is will silica dissolve in water coming from basalt? All the silica deposits I have seen come from felsic ground, but that is hardly surprising because it is that that makes up Earth’s land masses, and hot-spot eruptions, like in Hawaii, are too violent. So I need to know whether olivine and/or pyroxene could give soluble silica. If not, in my view, no life on Mars. I shall post outcomes of this conference in a couple of weeks or so.

      • BTW, why should life start with RNA? Synthetic biology has introduced new base pairs… Something simpler than DNA, OK… But DNA itself, in its exquisite detail, doesn’t look sacred. A scifi favorite is the poisonous life out there…

  2. So what you suggest is that Gale crater may just have been a 30,000 years event, a special, one time thing. Agreed, could have been. But, for various reasons, I believe Mars had standing water for a billion years, at least (which is the commonly accepted hypothesis).
    Main reason: Mars loses atmosphere during Coronal Mass Ejections. There may well have been LESS with the weaker sun. So atmosphere there was, thick enough for water.

    And that explains the giant water ice cliffs on Mars….

    On Earth the giant tides would have helped, as I said in the essay I just wrote (and before), by mixing earth, wind and fire. Violent conditions favor organic molecules, etc…. I just found this silly forum in which some papers I didn’t know of are mentioned… https://www.scienceforums.net/topic/35736-ancient-tides-and-life-origination/

    My own (!!!!) theory of Moon origination doesn’t use the giant impact, BTW, but the Moon forms at the Roche Limit… So very low, and Earth rotates. very fast… Giant tides again…

    Anyway you know things about of this I don’t even conceive of… Got to run now, but I shall think. Good luck with talk. My accompanying essay may have a whistle or bell of interest of cheer leading type, maybe…
    https://patriceayme.wordpress.com/2018/06/15/organics-on-mars-more-importantly-water-long-ago-now-ice-cliffs/

    • The evidence that I have seen relating to Mars is yes, it had standing fluid on Mars over a period of about a billion years, or maybe even longer, but it was intermittent. There were very few places that had fluid continually over more than a couple of hundred thousand years, and I think there were periodic major volcanic eruptions that sent out a lot of volatiles, and then these subsided and the fluid from to ice. My own theory (!!!!) is that the fluid was never water, but rather ammonia/water, which is fluid at about -80 degrees C. I know people like Sagan say ammonia is unstable to photodissociation and wouldn’t last more than a few decades but what he overlooked is ammonia is extremely soluble in water (like HCl gas, it can work a “fountain experiment”) so it wouldn’t be in the air, and the upper atmosphere would form a haze like Titan anyway. That atmosphere also contained methane, i.e. it was reduced. The geologists say that is not possible -their models show the \gas had to be CO2, however, there are samples of atmosphere trapped in rocks from Isua, Greenland, that are about 3.8 Gy old, and they have enclosed methane. Further, there is a sample of ancient seawater trapped in rocks from Barberton that are 3.2 Gy old, and they have ammonia levels about those of potassium. What would then happen is that methane would oxidise to CO2, which would react with ammonia to form ammonium carbonate, and if this was buried ti would first form urea, and then who knows. So my argument is the water flows on Mars probably were ammoniacal water, and the nitrogen from the ammonia is still buried under the surface. A prediction, but like many others, you have to dig in the right place and that is probably fairly deep because the low spots where water would flow to would subsequently be filled with dust, etc.

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