NASA’s Curiosity rover has unveiled the longest molecules ever found on Mars, revealing potential evidence of ancient life on the planet.
The rover detected molecule chains consisting of up to twelve carbon atoms linked together, in a rock sample estimated to be 3.7 billion years old, taken from a dried-up Martian lakebed called Yellowknife Bay.
This groundbreaking discovery, detailed in a study published on March 24 in the journal Proceedings of the National Academy of Sciences, opens new possibilities regarding the existence of life on Mars in ancient times.
Researchers believe that these long carbon chains stem from fatty acids, organic compounds typically produced by living organisms on Earth. While it is acknowledged that fatty acids can arise through non-biological processes, the presence of such molecules on Mars suggests that signs of life may still exist within its soil.
Caroline Freissinet, a co-author of the study and analytical chemist at the French National Centre for Scientific Research, remarked, “If life ever appeared on Mars billions of years ago, at the time life appeared on Earth, chemical traces of this ancient life could still be present today for us to detect.”
The hydrocarbon chains identified by Curiosity are comprised of molecules known as decane, undecane, and dodecane, which contain 10, 11, and 12 carbon atoms, respectively. These molecules were detected through the Sample Analysis at Mars (SAM) instrument.
Since its arrival on Mars in 2012, the Curiosity Rover has been traversing the Gale Crater, a massive impact crater formed by an ancient meteorite collision. Over the years, the rover has covered approximately 20 miles across the crater, exploring various locations such as Yellowknife Bay and the towering Mount Sharp.
The rock sample analyzed, nicknamed “Cumberland,” was drilled by Curiosity in 2013 from Yellowknife Bay, previously recognized for being rich in clay minerals, sulfur, and nitrates.
Despite numerous analyses over the past decade, the long hydrocarbon chains remained undetected until recently. Their discovery was somewhat serendipitous, occurring during an effort to identify amino acids, the building blocks of proteins, within the sample.
Researchers implemented a novel technique that involved pre-heating the sample to 1,100°C (2,012°F) before analysis. While their search for amino acids yielded no results, they fortuitously identified the long-sought fatty molecules.
Freissinet expressed her excitement upon seeing the spectral analysis results, noting, “It was both surprising and not surprising. Surprising because those results were found on the Cumberland sample that we had already analyzed many times in the past. Not surprising because we have defined a new strategy to analyze this sample.”
The scientists suggest that the detected molecules might have broken off from fatty acids like undecanoic acid, dodecanoic acid, and tridecanoic acid. Fatty acids are characterized by their long carbon and hydrogen chains, concluding with a carboxyl (-COOH) group.
To verify this hypothesis, the research team conducted an experiment in which undecanoic acid was mixed with a Mars-like clay and then analyzed similarly to prior SAM instrument tests. As anticipated, the undecanoic acid was observed to decompose into decane, supporting the theory that the carbon chains could have originated from fatty acids.
On Earth, the formation of such molecules is predominantly attributed to biological processes, although they can also arise through non-biological means. However, the researchers emphasize that non-biological processes typically yield fatty acids containing fewer than 12 carbon atoms.
Given that SAM detected carbon chains up to 12 carbons long, it suggests the potential existence of even longer chains, which the instrument may not be optimized to detect.
“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,” commented Daniel Glavin, co-author of the study and researcher at NASA’s Goddard Space Flight Center.
Regardless of the origins of these molecules, their detection and their likely connection to fatty acids confirm that Curiosity is capable of recognizing such compounds and indicates that these molecules can remain preserved in the Martian environment for billions of years.
The researchers express hope that future missions will allow for the return of Martian soil samples to Earth for thorough analysis, aiming to resolve the longstanding question of life on Mars once and for all.
Glavin stated, “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.”
image source from：https://www.livescience.com/space/mars/curiosity-rover-finds-largest-carbon-chains-on-mars-from-3-7-billion-year-old-rock
