Surprisingly big organic molecules on Mars: A hint of life?
NASA’s Curiosity rover has found the largest organic molecules on Mars we’ve yet seen. They seem to be the remains of fatty acids. Video via NASA Goddard.
- Did life ever exist on Mars? Rovers have found various types of organic molecules, but whether any of them relate to ancient life remains unknown.
- NASA’s Curiosity rover has now discovered the largest known organic molecules to date. They are three kinds of long-chained carbon molecules that scientists say are the remains of fatty acids. Fatty acids are common in life on Earth, but can also form without life.
- The complex carbon molecules are in mudstone rocks that used to be at the bottom of an ancient lake. Scientists don’t yet know how they formed, but they are certainly tantalizing.
Surprisingly large organic molecules on Mars
The prospects for ancient life on Mars might have just received a big boost. NASA’s Curiosity rover has discovered the largest organic molecules so far on the red planet. NASA said on March 24, 2025, that the molecules – thought to be fatty acids – contain chains of up to 12 carbon atoms. That’s significantly more complex than organic compounds previously found on Mars. On Earth, fatty acids help form cell membranes and assist with other biological functions. But non-biological processes can form them as well. So the discovery is tantalizing, although not yet proof of life.
The international team of researchers published their peer-reviewed finding in the Proceedings of the National Academy of Sciences on March 24, 2025.
Largest organic molecules on Mars
Curiosity found the molecules with its Sample Analysis at Mars (SAM) mini-lab onboard the rover. The molecules were in a sample of mudstone – a fine-grained sedimentary rock – nicknamed Cumberland, in a region called Yellowknife Bay. The rover first studied and drilled into Cumberland back in 2013. Yellowknife Bay seemed intriguing according to data from orbiters. And it’s in Gale crater, which used to be an ancient lake a few billion years ago.
Cumberland turned out to be a goldmine for scientists. Curiosity found it to be rich in clay minerals, sulfur and nitrates. Sulfur is ideal for preserving organic molecules. And both plant and animal life on Earth use nitrates.
Curiosity found the molecules inadvertently while doing other analysis work on the sample. The rover was looking for evidence of amino acids, the building blocks of proteins. It didn’t find any – but – it did find decane, undecane and dodecane, which are long-chain alkane molecules. The mission scientists thought they might have broken off larger molecules during the heating process in SAM.
The findings show that rovers can find evidence of past life on Mars. Caroline Freissinet, the lead study author and research scientist at the National Centre for Scientific Research (CNRS) in Guyancourt, France, said:
Our study proves that, even today, by analyzing Mars samples we could detect chemical signatures of past life, if it ever existed on Mars.
Remains of fatty acids?
The discovery excited scientists, because the decane, undecane and dodecane could be the remains of fatty acids. Fatty acids are another building block of life. They help form cell membranes and perform other biological functions as well. More specifically, the scientists thought the three molecules could be the remnants of the fatty acids called undecanoic acid, dodecanoic acid and tridecanoic acid, respectively.
To find out, the researchers needed to do some testing in the lab back on Earth. They mixed undecanoic acid into a Mars-like clay and conducted a SAM-like experiment on the sample. And, sure enough, after heating it the same way as in SAM on Mars, the undecanoic acid released decane, as they 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.
Monica Grady, a planetary scientist at the Open University in the U.K., told Science:
This is an amazing result. If these are breakdown products from carboxylic acids, then we are seeing something very exciting indeed.
NASA's Jet Propulsion Laboratory: Curiosity Rover Detects Largest Organic Molecules Found on Mars www.jpl.nasa.gov/news/nasas-c…
— AAS Press Office (@press.aas.org) 2025-03-24T22:37:03.307Z
Evidence of Martian life?
While the discovery of these molecules is exciting, scientists don’t know its specific source. They could be the remains of once-living cells, or they might have formed without life. Curiosity is limited in being able to determine which is the case. There might be even longer carbon chains in Cumberland, but the rover’s instruments aren’t ideal for findings them.
There is an interesting detail, however, that might suggest a biological origin. The “backbone” each of the three fatty acids – decane, undecane and dodecane – is a long straight chain of 11 to 13 carbon atoms. On Earth at least, non-biological fatty acids tend to have shorter chains of less than 12 carbon atoms.
Also, on Earth, fatty acids from living things tend to be even-numbered in terms of their carbon atoms. Interestingly, the undecane molecule would have originated from an even-numbered fatty acid, and it is slightly more abundant than the others in the Cumberland sample.
The fact that Gale crater used to be an ancient lake makes the findings all the more fascinating. Co-author Daniel Glavin at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said:
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.
As to the search for complex organics like fatty acids, Glavin told Science:
It’s been a long journey to this point. This is really searching for a needle in a haystack. There’s no question about it. We have three needles.
The limits of Curiosity’s lab analysis
In order to definitively determine the origin of the molecules, the samples would ideally need to be brought back to Earth. Scientists can only use Curiosity itself to analyze these particular samples. And its onboard lab, while powerful, has its limits for detecting the biological origins of molecules.
There might be a way around that, however. When Curiosity obtained the samples back in 2013, it collected two “doggie bags.” But the rover has only used one of them so far. Mission scientists think they might be able to tweak the onboard lab to search for a wider range of alkanes. That would help them better determine the ratio of even to uneven carbon atoms.
There are also plans for a future mission – Mars Sample Return – to bring back samples that the Perseverance rover has obtained. Some of those also show tantalizing hints of possible ancient microbial life. Glavin said:
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.
Bottom line: NASA’s Curiosity rover has discovered the most complex organic molecules ever seen on Mars, the remains of fatty acids up to an incredible 12 carbon atoms long.
Source: Long-chain alkanes preserved in a Martian mudstone
Read more: Curiosity rover reaches ancient ridge of mud and boulders
Read more: Life on Mars? Odd rings and spots tantalize scientists
The post Surprisingly big organic molecules on Mars: A hint of life? first appeared on EarthSky.