PREVIEW

Scientists have discovered the largest organic compounds ever detected on Mars, raising the prospects of life having been present on the red planet.

A team analysing pulverised rock onboard NASA’s Curiosity rover identified these complex compounds, according to findings published in the Proceedings of the National Academy of Sciences. The discovery suggests that prebiotic chemistry on Mars may have progressed further than previously thought.

The research team re-examined a rock sample within Curiosity’s Sample Analysis at Mars (SAM) mini-laboratory, identifying decane, undecane, and dodecane—compounds consisting of 10, 11, and 12 carbon atoms respectively. These molecules are believed to be fragments of fatty acids preserved within the Martian rock. On Earth, fatty acids serve as fundamental components of biological membranes and other essential biochemical processes.

Curiosity drilled into the rock target known as “Cumberland” on the 279th Martian day, or sol, of its mission (19 May 2013), collecting a powdered sample from within. The Mars Hand Lens Imager camera, mounted on the rover’s robotic arm, captured images of the drill hole, which measured approximately 1.6 cm (0.6 inches) in diameter and 6.5 cm (2.6 inches) deep.

Fatty acids can be produced by living organisms, but they can also arise through non-biological processes, such as interactions between water and minerals in hydrothermal vents. While the precise origin of the molecules detected remains uncertain, their presence alone is an exciting discovery for scientists.

Previous studies by Curiosity had detected smaller, simpler organic molecules. However, this new finding provides the first evidence of more complex organic chemistry on Mars, which could have supported the conditions necessary for life’s emergence.

The study also raises hopes that large organic molecules, including potential biosignatures—compounds that can only be formed by living organisms—could have been preserved on Mars despite the planet’s exposure to intense radiation and oxidation over millions of years.

Scientists believe this discovery strengthens the case for returning Martian samples to Earth for further analysis using more advanced laboratory equipment. “Our study proves that even today, by analysing Mars samples, we could detect chemical signatures of past life—if it ever existed on Mars,” said lead author Caroline Freissinet, a research scientist at the French National Centre for Scientific Research in Guyancourt, France.

Freissinet previously co-led a 2015 study that first conclusively identified Martian organic molecules in the same Cumberland sample. The sample has since undergone multiple analyses using different techniques within the SAM instrument.

Curiosity extracted the Cumberland sample from a region in Gale Crater known as “Yellowknife Bay,” an area resembling an ancient lakebed. Scientists had directed the rover there before it continued towards its primary target, Mount Sharp, which rises from the crater’s floor.

The detour yielded remarkable scientific value. Cumberland’s chemical composition provides tantalising insights into the 3.7-billion-year history of Gale Crater. The sample is rich in clay minerals, which form in water, as well as sulphur, which can aid in the preservation of organic molecules. Additionally, scientists have detected high levels of nitrates, which are essential for life on Earth, and methane containing a type of carbon often associated with biological processes.

This latest discovery strengthens the possibility that Mars once harboured conditions favourable to life and underscores the importance of continued exploration and sample return missions.