A nitrogen-bearing molecule with a structure similar to DNA precursors has been detected on Mars for the first time, the result of a chemical experiment never before performed on another world. The finding comes from NASA's Curiosity rover, which used a technique called TMAH to break apart larger organic molecules in a clay-rich region of Gale crater, revealing a diverse mix of chemicals that have been preserved for an estimated 3.5 billion years.
The experiment identified more than 20 organic molecules, including benzothiophene, a large sulfurous compound commonly delivered to planets by meteorites. The same meteoritic material that reached Mars also rained down on early Earth, where it likely contributed to the building blocks of life.
The discovery was made in 2020 in the Glen Torridon region, an ancient lake bed where clay minerals can trap and preserve organic compounds better than other materials. Curiosity landed in this crater in August 2012 with a mission to find evidence that ancient Mars had conditions capable of supporting microbial life billions of years ago.
Amy Williams, Ph.D., a professor of geological sciences at the University of Florida and scientist on both the Curiosity and Perseverance rover missions, helped develop the experiment.
Amy Williams:
"We think we're looking at organic matter that's been preserved on Mars for 3.5 billion years. 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."
The instrument suite that performed the experiment, Sample Analysis at Mars (SAM), has driven many of the mission's most significant discoveries about Martian organic chemistry and habitability. SAM is led in part by Jennifer Eigenbrode, Ph.D., an astrobiologist at NASA's Goddard Space Flight Center.
The TMAH chemical used to break apart the molecules is in critically short supply: Curiosity carries only two cups. Mission planners had to select the sampling location with extreme care.
The same technique is now planned for future missions, including the Rosalind Franklin mission to Mars and the Dragonfly expedition to Saturn's moon Titan.
Amy Williams, Ph.D. "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."
The experiment cannot determine whether these organic compounds originated from potential past life on Mars, formed through geologic processes, or arrived via meteorites. Definitive identification of biosignatures would require returning rock samples to Earth for analysis.
Williams noted that the presence of large complex organics in the shallow Martian subsurface raises the possibility that even larger molecules diagnostic of life could have survived.
Amy Williams, Ph.D.:
"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."
The Perseverance rover, which landed in 2021, continues the search for signs of ancient life and is caching samples for a potential future return mission.
DOI : 10.1038/s41467-026-70656-0