To answer David Bowie’s question that forever floats dreamily in space — is there life on Mars? — what we might need to ask beforehand is whether there is salt on Mars.
As many scientists will repeat ad nauseam, organics don’t necessarily mean aliens. Many organic compounds arise from abiological processes, but biologically produced organics could possibly be a sign of living organisms or all that remains of something extinct. This isn’t just sodium chloride, though NaCl is a necessary electrolyte lost through physical activity, which explains why you find it in Gatorade. Other salts like acetates and oxalates are fuel for some life-forms.
While NASA’s Curiosity rover continues to crawl over the reddish, radiation-blasted wasteland, organic geochemist James M.T. Lewis is in search of salts through its Sample Analysis at Mars (SAM) lab and Chemistry and Mineralogy Instrument (CheMin) on board. He led a study recently published in Journal of Geophysical Research: Planets.
“On Earth, life is one of the processes that can concentrate organic salts,” Lewis tells SYFY WIRE. “Any process on Mars that concentrates organic salts and organic matter is really interesting to us. We're saying that organic salts are a really good explanation for a lot of SAM data, but we aren't yet completely sure if they're present, and if they are, what forms they might be in.”
SAM investigates organic and inorganic chemistry on Mars, identifying compounds by heating them up until they release gases, which are then sent to its mass spectrometer to identify the chemicals they are made of. What gases are released at which temperatures can also tell Lewis’ team here on Earth what kind of chemistry they are looking at. Water and carbon dioxide vapors can support what CheMin — which is more focused on Martian minerals and the processes that formed them — sees. SAM has found organics while CheMin has not yet beamed down evidence of any.
While SAM can detect infinitesimal amounts of gases that CheMin is not capable of detecting at those levels, this doesn’t mean that it has definitely found organic salts. When these types of salts are heated, they produce gases that would also be released by other organic and inorganic substances. The reason that Lewis believes organic salts probably explain SAM data is because their behavior in a lab on Earth is extremely similar to what is shown by that data. CheMin also has a basis for comparison from our planet. It X-rays samples the same way it would to identify salts on terra firma.
CheMin should still be able to detect the same types of salts found on Earth if it comes across a high enough concentration in which crystalline structures have developed, but that could be problematic considering what kind of environment Curiosity is dealing with. Lewis is always having to put together fragments of organics that have been decimated so he can find out what larger molecules they may have once been part of.
“Because the atmosphere is very thin and Mars lacks a strong magnetic field, there are high levels of radiation, which can break down organic matter, affecting its preservation,” he says. " In some of our SAM experiments, we detected small organic fragments at very high temperatures, which tell us they were coming from big complex organic compounds that don't break down very easily.”
SAM at least revealed that there was sulfur in these fragments, and sulfur might be a preservative for organic matter that would otherwise take a beating on the surface of Mars, but there are more problems. Curiosity and other rovers and landers that have scoured the planet have also found what are believed to be inorganic perchlorate salts all over. If a sample containing these and organic matter is heated, the oxygen and chlorine they give off can react with organics and make them more difficult to detect.
If there is one thing Lewis wants to see in the future, it is satellites detecting regions on Mars with high salt concentrations salts, so spacecraft already on the surface can be sent to explore those areas. There are more places on the Red Planet that still need to be explored for signs of organic salts, especially what lies beneath the seemingly barren crust. Mars is thought to have once supported life before its atmosphere was just about obliterated. It is much more likely that hypothetical Martian microbes fled underground to escape being irradiated to death.
“We are still very much at the beginning of understanding the organic chemistry of Mars,” Lewis says, “but the organic fragments we've seen with SAM have given us insight into how organic matter could be surviving.”