Where Did the Organic Matter on Mars Come From?

Biology may not be required to explain the chemicals we see in Martian rocks and meteorites.

Curiosity found organics in Gale Crater on Mars. But is there or was there ever life?

In a new paper published in Science Advances, Andrew Steele from the Carnegie Institution of Science in Washington D.C. and colleagues suggest a chemical pathway for the formation of organic matter on Mars. Their research may help explain organic compounds found in Martian meteorites, and, more recently, at Gale Crater by the Curiosity Rover.

The scientists reported that brines—dense salt solutions—can form organic compounds if the brines contain carbon dioxide and certain iron minerals.

That bears on the question of whether life exists on Mars, because organic compounds are essential for life as we know it. Although different types of organic compounds have been found in Martian rocks, the question remains whether they were produced by living organisms (as suggested in the 1990s for the famous Martian meteorite ALH 84001, or more recently for the mudstones found at Gale Crater) or whether they’re of purely chemical origin.

Other scientists remain skeptical that organics are indigenous to Mars. In the case of Martian meteorites found on Earth, they think that organic compounds are the result of terrestrial contamination after the rocks arrived here. Organic compounds found on Mars were interpreted by them not to have originated there, but to have come from the infall of organic-rich comets and asteroids. But the pathway proposed by Steele and his colleagues would provide a way for organic compounds to be produced directly in the Martian environment. This may even have been common in the Red Planet’s past.

We know there are many salt-rich environments on Mars—places such as the Southern Highlands, where large chloride deposits exist. The presence of brines in puzzling features called Recurrent Slope Lineae has been suggested, and Mars has relatively high concentrations of perchlorates, strongly oxidizing salts that only occur in the driest deserts on Earth and Mars.

Steele and his colleagues have found a way for organic compounds to be produced in some environments on Mars, but the question is how effective that production really is. How often would it occur? Carbon dioxide and iron minerals are very common on Mars, but brines? And can the process explain the relatively high concentration of organic matter in some meteorites, or the diversity of organics found in meteorites and at Gale Crater?

More studies will be needed to answer these questions.

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