Giant string of organic molecules on Mars may be one of the best signs of life yet
Organic molecules discovered in a stone 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 proof of life on Earth. Marchthey warned.
In March 2025, scientists reported the discovery of the largest organic molecules never found on Mars. These long chains made of hydrogen and carbon can be fragments of fatty acids, often created by biological processes.
A discovery in the making for over a decade
The organic molecules in question are called alkanes. These are hydrocarbons, long chains of 10 to 12 carbon atoms with several hydrogen atoms attached to each carbon. If the endings of their names sound vaguely familiar, that’s because the alkane chemical family includes ethane, methane, propane, and butane, although they are much shorter chains. Alkane chains of 12 or more carbons are more likely to be produced by biological processes.
These tantalizingly large molecules are embedded in Cumberland mudstone, a fine-grained sedimentary rock located in an ancient Martian lake bed called Yellowknife Bay. Curiosity initially drilled this stone in 2013 and has since performed various analyzes using its onboard chemistry laboratory, the Sample Analysis at Mars instrument.
However, the researchers discovered the organic molecules only about a year ago, after preheating the sample to 2,012 degrees Fahrenheit (1,100 degrees Celsius) in search of amino acids. However, instead of the building blocks of proteins, they found traces of the largest organic molecules ever discovered on Mars.
Winding the clock on a Martian mudstone
In a recent study, researchers looked back in time at this sample, extrapolating the abundance of these molecules 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 damaging effects of radiation on the surface of Mars for about 80 million years. As a result, its organic materials were degraded by the bombardment of energetic particles from the sun and the universe in general.
“Given the geological history and thermal maturation of the organic materials preserved in the Cumberland sample, it is reasonable to assume that the recovered material represents only a fraction (perhaps several orders of magnitude less) of the primary lipid content that would have been entrained in the sedimentary unit during its deposition two and a half billion years ago,” the researchers explain in the paper.
Using previous radiolysis experiments as a gauge, the researchers calculated a “conservative” initial abundance of 120 to 7,700 ppb for alkanes, or the fatty acids from which they fragment. So, could abiotic sources account for substantial amounts of these substances, or were they formed by biological processes?
Researchers have evaluated numerous scenarios. First, they explored a space origin. Interplanetary dust particles (IDP) and meteorites frequently deliver organic molecules to the Martian surface. But the researchers concluded that these processes are unlikely to explain the abundance of organic material in the Cumberland sample, because IDPs cannot penetrate the rock and there are no signs of meteorite impacts.
In the second scenario, organic molecules settle to 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 smaller organic molecules. Fatty acid molecules can appear via a different pathway; but this requires high temperatures, and Cumberland shows no signs of having been properly heated.
Proof of extraterrestrial life?
Despite these dismissed theories, a non-biological process has held up: researchers cannot rule out that some organic matter formed abiotically in Hydrothermal systems on Mars and were transported to the surface by aqueous fluids rich in organic matter.
“To be clear, we are not claiming that evidence of ancient Martian life was found in the Cumberland mudstone,” the researchers said in the journal.
Yet the Cumberland sample is rich in many biologically involved molecular assets. These include clay minerals that form in the presence of water, nutrient nitrates, a type of carbon linked to biological processes, and sulfur that helps preserve organic molecules.
Gale Crater, the Yellowknife Bay site, has also held water for millions of years, apparently giving life-sustaining chemistry enough time to mix and match a multitude of molecules.
Yet the Curiosity rover could be limited in its ability to analyze even larger molecules – which are more likely to be associated with biological processes – because of how it must separate and identify them. Such analyses, even on Earth, “always involve compromises,” study co-author Maison Christopheprofessor of geosciences at the Penn State College of Earth and Mineral Sciences, told Live Science via email. “So Curiosity might be able to find larger organic molecules, but not with the [precision] this made the identification of these specific molecules convincing.
The next step will be to carry out experimental studies on Earth mimicking the Cumberland mudstone and Martian environment, to determine how organic molecules such as fatty acids respond to Martian conditions. (The ultimate goal is for scientists to get their hands on real Martian mudstone via a sample return mission to Mars, although this is currently a difficult project to achieve. murky proposition at best.)
The existence of past or present Martian life is also unclear, but there are reasons for optimism among ET aficionados. “The researchers say that because the nonbiological sources they studied cannot 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. statement.
Coincidentally, the microbial processes that could have produced these organic materials may have appeared on Earth around the same time, during the Archaean Aeon. Considering that the Perseverance rover also 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 abundance suggest a biological origin for ancient alkanes preserved in a Martian mudstone? Astrobiology15311074261417879. https://doi.org/10.1177/15311074261417879
