Perhaps most important, scientists determined that Yellowknife Bay was indeed the site of an ancient lake, providing an environment that could concentrate organic molecules and preserve them in fine-grained sedimentary rock called mudstone.
“There is evidence that liquid water existed in Gale Crater for millions of years and probably much longer, which means there was enough time for life-forming chemistry to happen in these crater-lake environments on Mars,” said , senior scientist for sample return at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and a study co-author.
The recent organic compounds discovery was a side effect of an unrelated experiment to probe Cumberland for signs of amino acids, which are the building blocks of proteins. After heating the sample twice in SAM’s oven and then measuring the mass of the molecules released, the team saw no evidence of amino acids. But they noticed that the sample released small amounts of decane, undecane, and dodecane.
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Because these compounds could have broken off from larger molecules during heating, scientists worked backward to figure out what structures they may have come from. They hypothesized these molecules were remnants of the fatty acids undecanoic acid, dodecanoic acid, and tridecanoic acid, respectively.
The scientists tested their prediction in the lab, mixing undecanoic acid into a Mars-like clay and conducting a SAM-like experiment. After being heated, the undecanoic acid released decane, as predicted. The researchers then referenced experiments already published by other scientists to show that the undecane could have broken off from dodecanoic acid and dodecane from tridecanoic acid.
The authors found an additional intriguing detail in their study related to the number of carbon atoms that make up the presumed fatty acids in the sample. The backbone of each fatty acid is a long, straight chain of 11 to 13 carbons, depending on the molecule. Notably, non-biological processes typically make shorter fatty acids, with less than 12 carbons.
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It’s possible that the Cumberland sample has longer-chain fatty acids, the scientists say, but SAM is not optimized to detect longer chains.
Scientists say that, ultimately, there’s a limit to how much they can infer from molecule-hunting instruments that can be sent to Mars. “We are ready to take the next big step and bring Mars samples home to our labs to settle the debate about life on Mars,” said Glavin.
More About Curiosity
This research was funded by NASA’s Mars Exploration Program. Curiosity’s Mars Science Laboratory mission is led by NASA’s Jet Propulsion Laboratory in Southern California; JPL is managed by Caltech for NASA. SAM (Sample Analysis at Mars) was built and tested at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. CNES (the French Space Agency) funded and provided the gas chromatograph subsystem on SAM. Charles Malespin is SAM’s principal investigator.
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