The longest molecules ever found on Mars have been unearthed by NASA’s Curiosity rover, and they could mean the planet is strewn with evidence for ancient life.
Molecule chains containing up to twelve carbon atoms linked together were detected in a 3.7 billion-year-old rock sample collected from a dried-up Martian lakebed named Yellowknife Bay, according to a study published Monday (March 24) in the journal Proceedings of the National Academy of Sciences.
These long carbon chains are thought to have originated from molecules called fatty acids, which, on Earth, are produced by biological activity. While fatty acids can form without biological input, which may be the case on Mars, their existence on the Red Planet means that signs of life may be lurking within its soil.
“The fact that fragile linear molecules are still present at Mars’ surface 3.7 billion years after their formation allows us to make a new statement: If life ever appeared on Mars billions of years ago, at the time life appeared on the Earth, chemical traces of this ancient life could still be present today for us to detect,” study co-author Caroline Freissinet, an analytical chemist at the French National Centre for Scientific Research in the Laboratory for Atmospheres and Space Observations, told Live Science.
The molecules — hydrocarbon strings of 10, 11 and 12 carbon atoms called decane, undecane, and dodecane — were detected by Curiosity’s Sample Analysis at Mars (SAM) instrument.
No stone unturned
The Curiosity Rover arrived on Mars in 2012 at the Gale Crater, a massive 96-mile-wide (154 km-wide) impact crater formed by the planet’s collision with an ancient meteorite. In the years since, the rover has traveled about 20 miles (32 km) across the crater, investigating places including Yellowknife Bay and Mount Sharp (Aeolis Mons), a 3.4-mile-high (5.5 km-high) mountain in the center of the crater.
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Nicknamed “Cumberland”, the sample analyzed for the new study was drilled by Curiosity in 2013 from Yellowknife Bay, and previous analyses found it to be rich in clay minerals, sulfur, and nitrates.
But despite many thorough tests, the hydrocarbon strings in the sample remained undetected for more than a decade. The hydrocarbons were actually discovered by accident as part of an attempt to find the building blocks of proteins — known as amino acids — in the sample.
The researchers behind the new study thought to test out a new method for finding these molecules by pre-heating the sample to 1,100°C (2,012°F) to release oxygen before analysis. Their results showed no amino acids, but, by pure luck, they discovered the fatty molecules hiding there instead.
“The excitement was super high when I saw the peaks on the spectrum for the first time,” Freissinet said. “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.”
“New method, new results,” she added.
The researchers suggest that the molecules may have broken off from the long tails of fatty acids named undecanoic acid, dodecanoic acid, and tridecanoic acid, respectively. Fatty acids are long chains of carbon and hydrogen with a carboxyl (-COOH) acid group at the end.
Life-forming chemistry
To test this theory, the researchers mixed undecanoic acid into a Mars-like clay in the lab before performing a test similar to that carried out by the SAM instrument As expected, the undecanoic acid broke down to decane, indicating that the carbon chains could indeed have originated from fatty acids.
On Earth, molecules like these are overwhelmingly produced by biological processes, but they can also occur naturally without life. However, non-biological processes usually only result in fatty acids with fewer than 12 carbon atoms, the researchers say. While the longest carbon chain detected by SAM had 12 carbons, the instrument is not optimized to detect longer molecules, meaning that it is possible longer chains were also present.
“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,” study co-author Daniel Glavin, a researcher at NASA’s Goddard Space Flight Center, said in a NASA statement.
Regardless of what made them, the detection of the carbon chains and their likely origins as fatty acids confirms that Curiosity can detect molecules of this kind, and that the molecules can remain preserved for billions of years in the Martian environment. The researchers hope to one day bring samples of Martian soil back home to Earth to properly analyze the contents, and hopefully solve the mystery of the Red Planet’s elusive life once and for all.
“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.
