Organic molecules discovered in a rock on Mars cannot be fully explained by non-biological processes, and it is “reasonable to assume” that living things could have formed these strange organic molecules, a NASA-led team reports in a new study. However, this does not mean that scientists have found definitive evidence that life continues Marchthey warned.
In March 2025, scientists reported the discovery of the largest organic molecules ever found on Mars. These long chains made of hydrogen and carbon can be fragments of fatty acids, which are often created through biological processes.
A discovery for more than ten years
The relevant organic molecules are called alkanes. They are hydrocarbons, long chains of 10 to 12 carbon atoms with several hydrogen atoms attached to each carbon. If the ends of their names sound vaguely familiar, that’s because the alkane chemical family includes ethane, methane, propane, and butane—although these are much shorter chains. Alkane chains of 12 carbons or more are more likely to be made by biological processes.
These tantalizingly large molecules are embedded in Cumberland mudstone, a fine-grained sedimentary rock in an ancient Martian lake named Yellowknife Bay. Curiosity originally drilled into this rock back in 2013 and has since performed various analyzes using its on-board chemistry laboratory, the Sample Analysis at Mars instrument.
However, scientists discovered the organic molecules just a year ago, after preheating the sample to 2,012 degrees Fahrenheit (1,100 degrees Celsius) in a search for amino acids. Instead of the building blocks of proteins, however, they found traces of the largest organic molecules ever discovered on Mars.
Rewind the clock on a mud stone from March
In the recent study, researchers turned back the clock on this sample, extrapolating how many of these molecules would have been billions of years ago when they were deposited in the mudstone.
The alkanes in the sample have a measured abundance of 30 to 50 parts per billion (ppb), but the Cumberland mudstone has been exposed to the harsh effects of radiation on the Martian surface for about 80 million years. As a result, its organic matter has been degraded by the perpetual bombardment of energetic particles from the sun and from the universe at large.
“Given the geological history and thermal maturation of the organic matter preserved in the Cumberland sample, it is reasonable to assume that the recovered material is only a fraction (possibly several orders of magnitude less) of the primary lipid content that would have been entrained in the sedimentary unit when it was deposited two and a half billion years ago,” the researchers explained in the paper.
Using previous radiolysis experiments as a gauge, the researchers calculated a “conservative” initial abundance of 120 to 7,700 ppb for the alkanes, or fatty acids they fragmented from. So, could abiotic sources account for significant amounts of these substances, or were they formed through biological processes?
The researchers considered a number of scenarios. First, they explored a space-based origin. Interplanetary dust particles (IDPs) and meteorites often deliver organic molecules to the surface of Mars. But the researchers concluded that these processes are unlikely to account for the organic abundance in the Cumberland sample because IDPs cannot penetrate rock and there is no evidence of a meteorite impact.
In the second scenario, organic molecules settle on the surface after separating from the atmosphere, but Mars’ ancient atmospheric haze was not hazy enough to explain the observed abundance.
Water-rock interactions could have contributed, but they generally produce less organic molecules. Fatty acid molecules can arise via another pathway; but it requires high temperatures, and Cumberland shows no signs of having been properly warmed.
Evidence of alien life?
Despite these ruled out theories, a non-biological process held water: the scientists cannot rule out that some of the organics were formed abiotically in Martian hydrothermal systems and was transported to the surface by aqueous, organic-rich fluids.
“To be clear, we are not claiming that evidence of ancient life on Mars was found in the Cumberland mudstone,” the researchers said in the paper.
Nevertheless, the Cumberland sample is rich in many biologically implicated molecular tidbits. These include clay minerals that form in the presence of water, nutrient-rich nitrates, a type of carbon linked to biological processes, and the sulfur that helps preserve organic molecules.
Gale Crater, the site of Yellowknife Bay, also held water for countless millions of years, apparently giving life-forming chemistry plenty of time to mix and match a multitude of molecules.
Still, the Curiosity rover may be limited in its ability to analyze even larger molecules — which are more likely to be associated with biological processes — because of the way it must separate and identify them. Analyzes like these, even on Earth, “always have trade-offs,” study co-author Christopher’s houseprofessor of geosciences at Penn State’s College of Earth and Mineral Sciences, told LiveScience via email. “So, Curiosity might be able to find larger organic molecules, but not with the (precision) that made the identification of these specific molecules compelling.”
The next step is to conduct experimental studies on Earth that mimic Cumberland mudstone and the Martian environment, to determine how organic molecules such as fatty acids respond to conditions on Mars. (The ultimate goal is for scientists to get hold of some real Martian mudstones via a Mars sample return mission, although currently a lurid propositions at best.)
The existence of past or present Martian life is also nebulous, but there is cause for optimism among ET enthusiasts. “The researchers say that since the non-biological sources they considered could not fully explain the abundance of organic compounds, it is therefore reasonable to assume that living things could have formed them,” NASA officials said in a statement.
Coincidentally, the microbial processes that could have produced these organic substances may have appeared on Earth around the same time, during Archaic Eon. Considering that the Perseverance rover too discovered potential biosignatures in 2025the answer to the ultimate question is more alluring than ever.
Pavlov, AA, Freissinet, C., Glavin, DP, House, CH, Stern, JC, McAdam, AC, Roussel, A., Dworkin, JP, Chou, L., Steele, A., Mahaffy, PR, Buckner, D., & Gomez, F. (2026). Does the measured amount suggest a biological origin for the ancient alkanes preserved in a Martian mudstone? Astrobiology15311074261417879. https://doi.org/10.1177/15311074261417879
