Curiosity finds largest-ever organic molecules on Mars

The Mars Curiosity rover’s onboard mini-lab has helped confirm the existence of the largest organic molecules ever found on the Red Planet. The trio of long-chain compounds preserved in Martian soil are believed to be the remnants of prebiotic components required for life to develop on Earth. Researchers published evidence on March 24 in the Proceedings of the National Academy of Sciences, which builds on their work that began over a decade ago.

In May 2013, Curiosity started drilling into an area known as “Yellowknife Bay” in the Gale Crater. Scientists were interested in examining the region not for what it is today, but for what it may have been millions of years ago. Yellowknife Bay wasn’t a randomly chosen name—the arid and desolate landscape’s features still hint at a large, long-evaporated lakebed.

Curiosity’s soil survey, nicknamed “Cumberland,” has been analyzed multiple times inside its Sample Analysis on Mars (SAM) onboard mini-lab and has yielded a trove of new information about the planet’s past. In particular, it is rich in clay minerals that often form in water, and contains sufficient amounts of sulfur to help preserve organic molecules. Cumberland also features nitrates crucial to healthy animal and plant life, as well as methane containing a specific type of carbon associated with biological processes.

Most striking, though, was conclusive confirmation that Yellowknife Bay once hosted an ancient lake, further supporting the theory that Mars was once home to life of some kind.

Experts have since spent years examining data gleaned from SAM mini-lab analyses. In one recent experiment, a team including Glavin and Caroline Freissinet, an astrobiologist at the French National Center for Scientific Research worked to locate evidence of amino acids inside the Cumberland sample. While they didn’t find them that time, something else caught their eye: trace amounts of three carbon-chain molecules known as a decane, undecane, and dodecane. With 10, 11, and 12 carbons respectively, researchers believe these organic compounds may be residual fragments of fatty acids needed for cell membrane formation and other biological functions.

These fatty acids aren’t always definitive proof of life, however. Geological events like water-mineral interactions in hydrothermal vents can also produce similar molecules. That said, the length of many of the Cumberland soil carbon-chains could suggest otherwise. Depending on the molecule, organic life fatty acids often contain chains of 11-13 carbon atoms, while non-biological fatty acids usually contain 12 or fewer carbons. This means that at least some of the large organic molecules detected by Freissinet’s team may have once existed in organic life. What’s more, the discovery eases worries that Martian biosignatures couldn’t survive tens of millions of years of exposure to destructive oxidation and radiation.

“Our study proves that, even today, by analyzing Mars samples we could detect chemical signatures of past life, if it ever existed on Mars,” Freissinet, who also served as the latest study’s lead author, said in a statement.

“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,”  added Daniel Glavin, study co-author and sample return senior scientist at NASA’s Goddard Space Flight Center.

Unfortunately, Freissinet and colleagues can only discover so much using Curiosity’s SAM mini-lab. Organic fatty acid chains are often much longer than just 12 carbons, but the rover’s equipment isn’t designed to detect those. Luckily, NASA is ready and willing to assist in the next chapter of Martian exploration.

“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,” Glavin said.

Glavin, Freissinet, and colleagues may be waiting a while for that next step, however. While NASA has long planned on a Mars Sample Return mission, a ballooning budget and an uncertain future may push the project as far back as 2040.

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