Organic Material on Mars—The Case Gets Stronger

Contamination from Earth now seems less likely at the Curiosity landing site.

The Sheepbed mudstone, an ancient habitable lake in Gale Crater on Mars.

At the recent Lunar and Planetary Science Conference in Texas, two research groups led by Caroline Freissinet and Daniel Glavin made the scientific case for Martian organic material much stronger, based on new insights from the Sample Analysis at Mars (SAM) instrument on NASA’s Curiosity rover.

Curiosity already had found chlorinated organic matter—probably chlorinated by a reaction with perchlorates—on Mars. But it wasn’t clear whether the organic compounds derived from terrestrial contamination that the SAM instrument brought with it, or from indigenous Martian material. New analysis at various sampling sites indicates that, due to the relatively high detection signal, the organic material is most likely indigenous to Mars. The distinctly larger amounts of chloromethane and dichloroethane at the Sheepbed mudstone, compared to the sandy Rocknest site, suggests a Martian source of organic carbon.

This is in line with what we observe on Earth. Organic carbon is seen much more in clay and muds than it is in sandy material. And the Sheepbed mudstone already has been identified as the remnant of an ancient habitable lake.

Significantly, the organic carbon on Mars consists of reduced organic compounds, which could readily be used as building blocks for life. After the experiments on the Viking landers in the 1970s, many scientists thought that the Martian surface is oxidized, perhaps down to a significant depth. This view is clearly incorrect, and it appears more and more that Mars, or at least certain parts of the planet, were at some point in the past quite friendly to life.

Whether the organic compounds found by Curiosity came from putative Martian microorganisms cannot be determined at this time. They could just be organic material that fell to the surface in meteorites. But what’s becoming more certain is that organic material was, and still is, available on Mars in a form that could be used by microorganisms. In other words, microorganisms could clearly have made a living in the lake that would become the Sheepbed mudstone. The question then becomes: Are they possibly still there, perhaps hidden in a mud layer or underneath an ice patch, possibly in a dormant form? That’s a great question for Curiosity, or some future Mars mission, to address.

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