Curiosity rover detects diverse organics on Mars, including compound akin to DNA-building chemicals

In a first-of-its-kind chemical experiment performed on another planet, NASA's Curiosity rover has identified a surprising range of organic molecules in ancient Martian rocks — including a nitrogen-containing compound with a structure similar to chemicals involved in building DNA.

The results indicate that parts of the Martian surface can preserve molecules that could serve as potential signs of ancient life, though their origins remain unresolved. The research, led by Amy Williams, Ph.D., a geological sciences professor at the University of Florida and a member of the Curiosity and Perseverance science teams, was published April 21 in Nature Communications.

“We think we’re looking at organic matter that’s been preserved on Mars for 3.5 billion years,” Williams said. “It’s really useful to have evidence that ancient organic matter is preserved, because that is a way to assess the habitability of an environment. And if we want to search for evidence of life in the form of preserved organic carbon, this demonstrates it’s possible.” Curiosity’s analysis identified more than 20 chemicals.

Among them was the nitrogen-bearing molecule, never before detected on Mars, and benzothiophene, a large sulfur-containing molecule with two connected rings that is commonly delivered to planets by meteorites. “The same stuff that rained down on Mars from meteorites is what rained down on Earth, and it probably provided the building blocks for life as we know it on our planet,” Williams said.

However, the experiment cannot determine whether the organic compounds came from past life on Mars, natural geological processes, or meteorites. Scientists say confirming any true evidence of past life would require bringing Martian rock samples back to Earth for detailed study.

The experiment was conducted in 2020 in Glen Torridon, a clay-rich region within Gale crater — an ancient lake bed where clays formed in the presence of water and are known to trap and preserve organic material. Curiosity, operated by NASA’s Jet Propulsion Laboratory, has explored Gale crater since landing in August 2012 to assess whether Mars once had conditions suitable for microbial life.

The work relied on the rover’s Sample Analysis at Mars instrument suite, known as SAM, whose team includes co-author Jennifer Eigenbrode, Ph.D., an astrobiologist at NASA’s Goddard Space Flight Center. Using a chemical called TMAH, the team broke down larger organic molecules into smaller fragments that SAM could examine.

Because Curiosity carries only about two cups of TMAH, researchers carefully selected the sampling site and timing for the test. The findings are shaping plans for upcoming missions. The Rosalind Franklin rover on Mars and the Dragonfly mission to Saturn’s moon Titan are expected to carry similar TMAH-based experiments to search for organic compounds.

“We now know that there are big complex organics preserved in the shallow subsurface of Mars, and that holds a lot of promise for preserving large complex organics that might be diagnostic of life,” Williams said.

While Perseverance, which landed in 2021, focuses on seeking direct signs of ancient life, Curiosity’s new results suggest that Mars’ shallow subsurface can safeguard complex carbon chemistry — and that future sample-return efforts could provide the clarity scientists seek.