a gif shows martian ground followed by a hole drilled into it and surrounded by dust
In 2013, the Curiosity rover drilled this hole, which measures about 0.6 inches wide and 2.6 inches deep, into martian rock. The sample is now thought to contain long-chain organic molecules.
When scientists revisited an old Martian rock sample collected by NASA’s Curiosity rover, they were initially hunting for evidence of amino acids, the building blocks of proteins. But they ended up discovering something else entirely: the largest organic compounds ever documented on Mars. The compounds date to 3.7 billion years ago—around the same time that life first emerged on Earth.
Although they could have been formed by either biological or non-biological activity, these compounds join a host of other tantalizing clues to the potential existence of ancient Martian life. The discovery is detailed in a study published Monday in the journal P roceedings of the N ational A cademy of S ciences.
Curiosity collected the sample in 2013 from a rock dubbed Cumberland, at the site of a bygone lake now known as Yellowknife Bay. By re-examining this pulverized rock, the researchers were surprised to discover the hydrocarbon molecules decane, undecane and dodecane—which contain chains of carbon atoms in groups of 10, 11 and 12, respectively.
The rover’s on-board mini lab had burnt the molecules down while processing the rock sample, but the team suspects they may have originally been parts of carboxylic acids, or fatty acids. On Earth, fatty acids perform various functions in living organisms, including the formation of cell membranes.
“This is an amazing result,” Monica Grady, a planetary scientist at the Open University in England who didn’t participate in the study, tells Science’s Paul Voosen. If the molecules truly are the broken-down leftovers of fatty acids, “then we are seeing something very exciting indeed,” she adds.
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To test the feasibility of this hypothesis, the researchers mixed a fatty acid into Mars-like clay and processed it in a lab back on Earth. They used an approach that’s akin to how Curiosity’s mini-lab processes rock on Mars—and as they’d suspected, it yielded the molecule decane. Previous studies also show that undecane and dodecane could have been produced in a similar manner. This adds strength to the idea that these molecules came from fatty acids.
While the existence of fatty acids does not necessarily point to life, it remains a real possibility. “If we have long-chain fatty acids on Mars, those could come—and it’s only one hypothesis—from membrane degradation of cells present 3.7 billion years ago,” lead author Caroline Freissinet, an analytical chemist at the Atmospheres and Space Observations Laboratory in France, tells the Guardian’s Ian Sample.
However, the fatty acids also “could have either been formed by geological processes on Mars (non-biological chemical reactions such as from hydrothermal activity) [… or] delivered to the surface of Mars from meteorites,” Daniel Glavin, a senior scientist for sample return at NASA’s Goddard Space Flight Center and a co-author of the study, explains to Gizmodo’s Isaac Shultz. “Or they are the organic remnants of an ancient Martian biology.”
The molecules do appear to show some promising patterns. Most fatty acids in Earth’s organisms have an even number of carbon atoms, so finding this feature on Mars could point to the potential existence of life. Undecane would have come from an even-numbered fatty acid—and intriguingly, the team documented a slightly higher presence of undecane compared to the other two molecules. Additionally, chemical (and hence non-biological) processes usually produce shorter fatty acids, with less than 12 carbons.
A graphic of the discovered organic molecules and a selfie from the Curiosity rover
A graphic of the discovered organic molecules and a selfie from the Curiosity rover
Even if the molecules didn’t originate from cells, the discovery remains important, because the large compounds suggest organic chemistry on Mars achieved higher complexity than what scientists had previously observed. It also confirms that potential evidence of life can survive on Mars for billions of years—long enough for scientists to discover it.
“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 says in a statement.
“The findings reported in this paper present the best chance we have seen for identifying the remains of life on Mars,” explains John Eiler, a geochemist at the California Institute of Technology who was not involved in the research, to the Guardian.
Still, scientists can’t make a conclusion from merely three molecules. And the kind of analyses that could reveal the origin of the fatty acids noted in the study require advanced instruments that Curiosity doesn’t have. Thus “sealing the deal absolutely requires return of such samples to Earth,” Eiler adds.
Luckily, NASA and the European Space Agency are currently working on a Mars Sample Return project, though its timeline is undetermined.
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Margherita Bassi | READ MORE
Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.
Filed Under: Aliens, Chemistry, Cool Finds, Geology, Mars, NASA, New Research, Outer Space, Planets, Solar System