NASA's Curiosity rover, analyzing a sample of Martian soil collected in March 2017, has identified two organic compounds—benzoic acid and ammonia—that have never before been detected on the planet's surface. The finding, published Monday in the journal Nature Astronomy, marks the first successful use of a wet chemistry experiment on Mars, a technique that mixes soil with chemical reagents to release and identify organic molecules.
The experiment, led by Maëva Millan, a postdoctoral fellow at NASA's Goddard Space Flight Center, involved directing the rover to mix the soil sample with reagents inside a specialized cup. The resulting chemical reaction released the organic molecules, which were then analyzed by the rover's onboard instruments. While the discovery does not confirm that life ever existed on Mars, it represents a significant step toward understanding the planet's past habitability.
“This experiment was definitely successful,” Millan told Inverse. “While we haven’t found what we were looking for, biosignatures, we showed that this technique is really promising.”
The study's authors noted that the experiment “has expanded the inventory of molecules present in Martian samples and demonstrated a powerful tool to further enable the search for polar organic molecules of biotic or prebiotic relevance.” Benzoic acid and ammonia, the two most prominent compounds detected, are both considered possible indicators of ancient biological or prebiotic activity.
Millan explained that the search for organic molecules on Mars is driven by a desire to understand the planet's past habitability and to look for bioindicators. The team is now focused on tracing the origins of these molecules, suggesting in the paper that they may have been produced by geological processes rather than biological ones.
This is not the first time Curiosity has found organic molecules in Martian soil, but the new results add to a growing list of such detections. Earlier this year, an international team of astrobiologists reported the presence of thiophenes—compounds found in coal, crude oil, and white truffles on Earth—in samples collected by Curiosity. That team suggested in March 2020 that thiophenes could be a sign of ancient life, though further research was needed to confirm.
Why This Matters for Mars Exploration
The successful wet chemistry test is a milestone for Mars sample analysis. Previous techniques used by Curiosity involved heating soil samples to release volatile compounds, but wet chemistry allows for the detection of larger, more complex organic molecules that might otherwise be missed. This capability is critical for the search for biosignatures, as many organic compounds that could indicate life are polar and would not vaporize easily.
The findings also come as NASA's Perseverance rover continues its own mission on Mars, collecting samples that could eventually be returned to Earth. Millan and her team are hopeful that Perseverance's advanced instruments will provide further insights into the organic molecules detected by Curiosity.
The study's publication in Nature Astronomy adds to a growing body of evidence that Mars once had the chemical building blocks for life. However, as Millan and her colleagues emphasize, the presence of organic molecules alone does not prove that life existed. The next step is to determine the sources of these molecules and whether they are linked to biological processes.
For now, the discovery underscores the value of innovative techniques in planetary exploration. As Millan put it, the experiment was a success not only for what it found but for what it enables future missions to do.
