Scientists using NASA’s Curiosity rover have discovered siderite—an iron carbonate—in the sulfate-rich rocks of Gale Crater, solving a long-standing mystery about Mars’ missing carbonates.
This find provides powerful new clues about the planet’s ancient atmosphere and supports theories that it once harbored conditions suitable for liquid water. The discovery challenges previous satellite data and suggests that more carbon may be hidden below the Martian surface or lost to space.
Rethinking Mars’ Ancient Atmosphere
Scientists have long believed that Mars once had a thick, carbon dioxide-rich atmosphere and flowing liquid water on its surface. According to that theory, the CO2 and water should have reacted with the planet’s rocks to form carbonate minerals. But until recently, surface analyses by rovers and orbital instruments using near-infrared spectroscopy hadn’t detected the expected levels of carbonate.
Now, new findings reported in Science reveal otherwise. Data from three drill sites examined by NASA’s Curiosity rover show the presence of siderite—an iron-based carbonate mineral—within sulfate-rich rock layers on Mount Sharp, located in Gale Crater.
A Surprising Find Beneath the Surface
“The discovery of abundant siderite in Gale Crater represents both a surprising and important breakthrough in our understanding of the geologic and atmospheric evolution of Mars,” said Benjamin Tutolo, associate professor at the University of Calgary, Canada, and lead author of the paper.
To investigate the mineral composition of the Martian surface, Curiosity drills a few centimeters into the ground and collects powdered rock samples. These samples are analyzed by CheMin, an onboard instrument developed by NASA’s Ames Research Center. CheMin uses X-ray diffraction to determine the mineral structure of the rocks, with further analysis carried out by scientists at NASA’s Johnson Space Center in Houston.
X-Ray Insights into Ancient Mars
“Drilling through the layered Martian surface is like going through a history book,” said Thomas Bristow, research scientist at NASA Ames and coauthor of the paper. “Just a few centimeters down gives us a good idea of the minerals that formed at or close to the surface around 3.5 billion years ago.”
The discovery of this carbonate mineral in rocks beneath the surface suggests that carbonate may be masked by other minerals in near-infrared satellite analysis. If other sulfate-rich layers across Mars also contain carbonates, the amount of stored carbon dioxide would be a fraction of that needed in the ancient atmosphere to create conditions warm enough to support liquid water. The rest could be hidden in other deposits or have been lost to space over time.
What’s Next for Mars Exploration
In the future, missions or analyses of other sulfate-rich areas on Mars could confirm these findings and help us better understand the planet’s early history and how it transformed as its atmosphere was lost.
Explore Further: NASA’s Curiosity Rover Digs Up a Carbon Time Capsule on Mars
Reference: “Carbonates identified by the Curiosity rover indicate a carbon cycle operated on ancient Mars” by Benjamin M. Tutolo, Elisabeth M. Hausrath, Edwin S. Kite, Elizabeth B. Rampe, Thomas F. Bristow, Robert T. Downs, Allan Treiman, Tanya S. Peretyazhko, Michael T. Thorpe, John P. Grotzinger, Amelie L. Roberts, P. Douglas Archer, David J. Des Marais, David F. Blake, David T. Vaniman, Shaunna M. Morrison, Steve Chipera, Robert M. Hazen, Richard V. Morris, Valerie M. Tu, Sarah L. Simpson, Aditi Pandey, Albert Yen, Stephen R. Larter, Patricia Craig, Nicholas Castle, Douglas W. Ming, Johannes M. Meusburger, Abigail A. Fraeman, David G. Burtt, Heather B. Franz, Brad Sutter, Joanna V. Clark, William Rapin, John C. Bridges, Matteo Loche, Patrick Gasda, Jens Frydenvang and Ashwin R. Vasavada, 17 April 2025, Science.
DOI: 10.1126/science.ado9966
Curiosity is a car-sized rover that’s part of NASA’s Mars Exploration Program (MEP), designed to explore the geology and climate of Mars and assess whether the planet ever had conditions suitable for life. The rover was built by NASA’s Jet Propulsion Laboratory (JPL), which is managed by Caltech in Pasadena, California. JPL also leads the mission operations on behalf of NASA’s Science Mission Directorate in Washington. Since landing in Gale Crater in 2012, Curiosity has been using advanced instruments to analyze Martian rocks, soil, and atmosphere, providing key insights into the planet’s ancient environment and its potential habitability.
