Ever since NASA made a huge revelation in a hurriedly convened press conference in 2018 about Mars Curiosity rover identifying ancient organic molecules embedded within 3-billion-year-old sedimentary rocks in Gale Crater, the tempo has remained high over every discovery made by the rover.
In 2018, NASA announced that the rover had detected ancient organic molecules, including thiophenes, benzene, toluene, and small carbon chains like propane or butene, embedded within 3-billion-year-old sedimentary rocks in Gale Crater. These findings suggested that Mars had the right conditions to support life in its distant past.
In 2021, another discovery revealed the presence of organic salts, which may be remnants of ancient biological material or products of geological processes. Scientists suggested that organic matter on Mars could be more widespread and better preserved than previously believed.
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By June 2022, Curiosity measured total organic carbon in Martian rocks for the first time, recording levels between 200 to 273 parts per million—similar to some of Earth’s most extreme environments, such as the Atacama Desert. This reinforced the idea that Gale Crater once had habitable conditions.
Now, in its most significant finding yet, NASA announced that Curiosity has identified the largest organic molecules ever detected on Mars. When scientists analyzed a rock sample inside the rover’s Sample Analysis at Mars (SAM) mini-lab, they found decane, undecane, and dodecane—compounds made up of 10, 11, and 12 carbon atoms, respectively.
These molecules are thought to be fragments of fatty acids, which on Earth are key building blocks of life. While fatty acids play a vital role in forming cell membranes and supporting biological functions, they can also emerge from non-biological processes, such as water interacting with minerals in hydrothermal vents. The source of these molecules remains uncertain, but their presence marks a major leap in Martian organic chemistry.
Previously, Curiosity had only detected small, simple organic molecules on Mars and the new discovery of larger, more complex compounds significantly increases the chances that biosignatures—large organic molecules that, on Earth, are exclusively created by life—may be preserved on Mars.
Moreover, the findings ease concerns that such compounds would be destroyed after millions of years of exposure to intense radiation and oxidation, thus strengthening the case for bringing Martian samples to Earth for deeper analysis using advanced scientific instruments.
“Our study proves that, even today, by analyzing Mars samples, we could detect chemical signatures of past life—if it ever existed on Mars,” said Caroline Freissinet, lead author of the study at the French National Centre for Scientific Research in Guyancourt, France. Previously he co-led a 2015 study that first confirmed the presence of Martian organic molecules in the same sample analyzed in this study.
The sample, known as “Cumberland,” has been repeatedly examined with different techniques using the SAM instrument. Curiosity drilled the Cumberland sample in May 2013 from Yellowknife Bay, an ancient lakebed in Gale Crater. Scientists were so intrigued by this location that they redirected the rover there before continuing to its primary destination, Mount Sharp. The detour proved invaluable—Cumberland contained a treasure trove of chemical clues about Gale Crater’s 3.7-billion-year-old past.
The sample was rich in clay minerals, which form in water, as well as sulfur, which helps preserve organic molecules. It also contained high levels of nitrates—essential for plant and animal life on Earth—and methane, often linked to biological processes. Most significantly, scientists confirmed that Yellowknife Bay was indeed the site of an ancient lake, providing the ideal conditions to concentrate and preserve organic molecules in fine-grained sedimentary rock known as mudstone.
“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,” said Daniel Glavin, senior scientist for sample return at NASA’s Goddard Space Flight Center.
Unexpected breakthrough in the hunt for life
This discovery was an unexpected outcome of an experiment originally designed to search for amino acids, the building blocks of proteins. Scientists heated the Cumberland sample twice in SAM’s oven and analyzed the molecules released. While no amino acids were found, small amounts of decane, undecane, and dodecane were detected.
Because these compounds may have broken off from larger molecules during heating, researchers worked backward to determine their original structures. They hypothesized that these molecules were remnants of the fatty acids undecanoic acid, dodecanoic acid, and tridecanoic acid.
To test this theory, scientists conducted a laboratory experiment, mixing undecanoic acid with Mars-like clay and subjecting it to the same heating process used in SAM. As expected, the undecanoic acid released decane, confirming their prediction. Previous studies also showed that undecane could have broken off from dodecanoic acid, and dodecane from tridecanoic acid, further supporting their findings.
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One particularly intriguing detail emerged from the study—the number of carbon atoms in the presumed fatty acids. Each contained a backbone of 11 to 13 carbon atoms, a pattern significant because non-biological processes typically produce shorter fatty acids with fewer than 12 carbon atoms. It raises the possibility that longer-chain fatty acids—potentially linked to biological activity—may exist on Mars.
However, SAM is not optimized to detect even longer-chain molecules, leaving open the question of whether more complex organic structures remain hidden in Martian samples.“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,” said Glavin.
Otherwise, these discoveries collectively suggest that Mars may have once been habitable, laying the foundation for future missions aimed at unraveling the planet’s history and its potential for past life.