Image above: Selfie of Curiosity rover showing the three carbon chains found next to it. source: NASA/Dan Gallagher
Article source: NASA 24/03/2025 publication
NASA now comes with a striking news: Remnants of fatty acids have been found in the ancient ‘Cumberland’ soil sample taken by rover Curiosity in 2013 in Yellowknife Bay, an ancient lake bed of Gale Crater (age 3.7GA). This detection was obviously done in the lab aboard the rover on site. The scientists were apparently looking for traces of amino acids (were they perhaps inspired by the recent finds in the samples from Bennu?), but found three long carbon chains in their place: decane, undecane, dodecane. So these are simple alkanes, but with lengths of 10, 11 and 12 carbons. This is remarkable, because as far as we know, fatty acids with 12 or more carbons are only formed biologically on Earth. Shorter fatty acids do sometimes form from purely geological processes, especially in hydrothermal sources. The researchers note this in the article, but do not make any further decision about it either. It is called “exciting” though. Yellowknife Bay is a place where other organic molecules were found, where methane was detected, and where there is a lot of nitrate in the soil (nutrients). We are sure there was a lake there for millions of years. In turn, the high sulphur content allows for better preservation of fossil organics.
The alkanes found come from fatty acids of the same length. This is evident from tests the researchers did with the fatty acids in question in a simulation of the Mars sample on which the same procedure was applied as in the Curiosity lab SAM. Possibly, it is even possible that there were even longer chains in the soil sample, but the SAM lab on Mars cannot detect them. An ‘on board lab’ always has a lot of limits.
What may also be noteworthy: Undecane is more numerous in the sample than the other two. Enzymes of terrestrial living things that build fatty acids do so per two carbons. Biological fatty acids therefore usually have an even number of carbons. If you then subtract the ‘acid head’ from that (CO2 splits off), you end up with an alkane with an odd number of carbons. So like undecane for example…. The researchers plan to look for even more fatty acids, to see if an excess of odd-numbered alkanes would come out of that too. Spicy detail: there is now only 1 partial sample left from Cumberland, the only sampling from which such promising finds have come. Nor does the rover have enough time and energy left to return to the sampling site.
For me, it raises some additional questions that are not answered in the NASA article. If these molecules were from living cells in the former lake, is it realistic that they could have been preserved for billions of years? It is a shallow bottom sample, so surely subject to conditions such as high-energy radiation, extreme temperatures, dehydration, etc. The soil sample has also been on board the Mars rover for 12 years. It seems a bit strange that these molecules have not been detected before. No doubt the scientists involved have good answers to these questions, but for now I have not found them.
Their conclusion is clear: Interesting, but we have no evidence that they would be traces of life. We know too little for that. The fatty acids could, for instance, have come onto the planet via impacting meteors, or formed later from the kerogen-like molecules (previously found in the same place on Mars) via as yet unknown chemical processes. Or might they have come from the rover itself, for instance from lubricants on the drill head? NASA scientists did manage to rule out the latter via extensive tests on SAM’s copy in their own lab.
But it does show that soil samples from Mars have great potential to find traces of (fossil) life if there are any, should we be able to apply better research techniques. In other words, we are hugely looking forward to the samples being sent to Earth in the early 1930s via NASA and ESA’s Mars Sample Return mission together. Then there could well be real answers to the question of whether life ever existed on Mars.