Fingerprints of Martian Life

Recent discoveries by the Curiosity rover reset the debate about life on Mars.

Curiosity has found what it went looking for.

Bombshell discoveries by NASA’s Curiosity Rover on Mars were reported today in two papers published in the journal Science. First, Jen Eigenbrode from the Goddard Space Flight Center and her team presented the first conclusive evidence of organic compounds on Mars. Second, Christopher Webster from Caltech and his team provided evidence that detected methane concentrations on Mars follow strong seasonal variations.

The first discovery will surely re-ignite the search for life on Mars. Eigenbrode and her colleagues looked at data from samples analyzed by Curiosity’s Sample Analysis at Mars (SAM) instrument suite, one of the main experiments on the rover that is now in its sixth year of exploring Gale Crater. They focused their analysis on an ancient lake that existed 3.5 billion years ago, now represented in the geological record by the Murray formation. In the mudstones of that formation SAM detected many large and complex organic molecules, which—amazingly—likely derived from even bigger organic macromolecules! Previously detected organics were only suggestive, not firm evidence, and only included chlorinated organic compounds that could also have originated from contamination.

Macromolecules such as proteins or nucleic acids (such as DNA) are the building blocks of life. While none of the organic compounds found on Mars necessarily resulted from biological processes, such compounds wouldn’t be expected near the Martian surface, because large molecules would break down rather quickly under the environmental conditions on Mars, particularly radiation. Intriguingly, many of the organic molecules detected by SAM have a sulfur group, which aids in preservation under these harsh conditions. One might wonder what we would find just a bit deeper below the surface, where organic molecules would have undergone less degradation.

Previous work had already established that the ancient lake on Mars was habitable. Now we know that it also contained organic compounds—so many of them, in fact, and of such diverse types, that Eigenbrode speculates heterotrophic organisms may have existed there in the past. In other words, Mars might have had an early ecosystem.

Webster’s paper in the same issue of Science supports this hypothesis by postulating that methane detected on Mars is consistent with small, localized releases from the Martian surface or subsurface. The detection of concentrated methane on Mars is a long-standing mystery. Could these methane releases be the tell-tale signs of an early biosphere on Mars, which remnants Eigenbrode discovered? Or could they even be caused by life processes occurring today?

The Viking Mars mission of the 1970s comes to mind—the only life detection experiments ever conducted on another planet. Scientists on that mission were puzzled by the results. Some of the experiments indicated microbial activity, while others did not, and the implications of those mixed results were argued over intensely. That made Viking’s non-detection of organic compounds a deciding factor, so that Gerald Soffen, project scientist for the Viking landers, finally and famously concluded, based on the apparent lack of organics: “No bodies, no life!”

I wonder what Soffen would say today!

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