NASA’s Curiosity rover has discovered the largest organic compounds ever seen on Mars, raising more questions about whether life may have once existed on the red planet.

Organic Compounds on Mars

NASA's Mars Curiosity rover (Image credit: NASA:JPL-Caltech)
NASA’s Mars Curiosity rover; Photo: NASA/JPL-Caltech

The compounds were detected in a 3.7 billion-year-old rock sample collected in Yellowknife Bay, an ancient Martian lakebed. Tests aboard the rover showed that the rock sample contained long-chain alkanes, which are organic molecules thought to be remnants of fatty acids.

Though these compounds can be made by lifeless chemical reactions, they’re also crucial constituents of cell membranes in all living organisms on Earth. Though this discovery doesn’t fully confirm life on Mars, it represents the best chance researchers have had of identifying the planet’s remains of life.

“These molecules can be made by chemistry or biology,” said Dr Caroline Freissinet, an analytical chemist who led the research at the Atmospheres and Space Observations Laboratory in Guyancourt, near Paris. “If we have long-chain fatty acids on Mars, those could come – and it’s only one hypothesis – from membrane degradation of cells present 3.7bn years ago.”

Testing Samples

The new study included Freissinet and her colleagues, who developed a new process to test more of the sample drilled from the mudstone. Curiosity detected large organics, including decane, undecane, and dodecane. Tests on Earth showed the rock likely contained carboxylic acids, or fatty acids, that converted to alkanes in the heating process.

“Although abiotic processes can form these acids, they are considered universal products of biochemistry, terrestrial, and perhaps Martian,” the scientists wrote in Proceedings of the National Academy of Sciences.

Scientists behind the study also noted that the Martian organics appeared to contain more even numbers than odd numbers of carbon atoms, similar to when organisms on Earth make fatty acids. This is because certain enzymes build fatty acids by adding two carbon atoms at a time.

Curiosity is currently carrying a second sample of the rock that researchers want to analyze for larger organics. Analyzing different isotopes of carbon and hydrogen in the organics could reveal more about their origins, but that would require a journey back to Earth.

“The findings reported in this paper present the best chance we have seen for identifying the remains of life on Mars,” said Eiler. “But sealing the deal absolutely requires [the] return of such samples to Earth.”