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.


Water on Mars!

Just after I write a blog on “The Martian”, NASA announces evidence for flowing water on Mars. Yes, the announcement probably was to spark some interest in NASA from the film Matt Damon is going to star in. The evidence seems to depend (and I have yet to see the relevant scientific papers) on some gullies carved in the side of one crater that grow when the temperatures are higher, and these gullies are best described in terms of water flow. The temperature of Mars is below the freezing point of water, and the air pressure is about half that needed for liquid water to exist, so how can this be? Where did this water come from?
There are various theories, one of them being there are underground aquifers where water flows, and these come to the surface. On a personal level, I cannot see this as being likely. An underground aquifer would still need heat to melt the water, and while there might be geochemical heat, why is this heat around craters? Actually, there are a number of craters on Mars that show signs of ancient water flow, and the usual explanation for these is that when the impact occurred, the heat of the impact melted any ice that was around, and this water was available to emerge from time to time, until it froze again. Various calculations suggest liquid water could be available from such impact heating for up to 50,000 years. However, if this were a new crater, and I understand it is not, we would still expect the water to emerge from anywhere along the side or bottom of the crater, and not specifically from near the top.
The most likely explanation I can come up with is that the water comes from the atmosphere. Actually, the atmosphere is quite humid; about 50%, and every now and again we even see cirrus clouds on Mars. The basic problem is that there is not very much air anyway. But, back to the question, how does water flow on Mars?
First, if you dissolve something else in water, the melting point is lowered, so this water is almost certainly a strong solution of something in water. Further, if you dissolve something in water, the boiling point is raised, or alternatively, the vapour pressure is lowered, by an amount dependent on how much solid is in the water. This is likely to be part of the answer, because there appears to be one new piece of information in the announcement. The gullies are not new, nor is the argument that they are caused by water flow, and I had references to that in my survey of information in Planetary Formation and Biogenesis, which was published as an ebook some years ago. No, what is new here is that there is spectral evidence for perchlorates in the bottom of the crater.
What seems to happen on Mars is that chlorides, which are rather common if water can concentrate them (the sea has quite a bit of sodium chloride), are oxidized, thanks to the hard ultraviolet radiation, to perchlorates. Magnesium perchlorate is deliquescent, that is, it sucks water out of the atmosphere and dissolves itself in it, and the melting point of the solutions will be quite lower. I don’t know what it would be, but calcium chloride, which is also deliquescent, when mixed with ice, melts the ice and lowers the temperatures to about minus 40 degrees. Magnesium perchlorate would probably do something similar.
What does that mean for life on Mars? As far as I am concerned, there is no change, and it might have got harder, the reason being that perchlorates are strong oxidizing agents, and may well interfere with certain life functions. Further, the solutions are saltier than “The Dead Sea”, and as the name suggests, it is not brimming with life.
This method of getting fluid water might also be thought to solve the problem of how to “make water” in the book, and presumably the film, “The Martian”. All you have to do is to distill off the water, then reuse the perchlorate. My personal view is this would be far too slow, and to get water, in my novel Red Gold I suggested simply pumping up the air pressure and squeezing/chilling the water out. Even better is finding ice, although that might be easier said than done in an emergency. So, while this announcement really makes little difference to the likelihood of finding life on Mars, it does make the chances of settling on Mars and surviving a little better.