NASA’s Curiosity rover, which has been driving around the surface of Mars for over 12 years, recently discovered a mineral called siderite on the slopes of Mount Sharp in Gale Crater. Interestingly, siderite might be the mineral that helps planetary scientists finally solve the mystery of where Mars’ carbon dioxide-rich atmosphere went.
Solving such a mystery could prove vital to understanding the red planet’s past and provide scientists with insight into how the atmosphere of Mars evolved to its current state.
Currently, Mars has a thin atmosphere composed of approximately 95% carbon dioxide. Scientists have long theorized that Mars’ atmosphere was once much thicker and rich with carbon dioxide. When coupled with flowing liquid water on the surface, this ancient atmosphere and water should have reacted with surface features to create carbonate materials. However, no missions to Mars have been able to identify such carbonate materials — until Curiosity’s latest discovery.
Curiosity’s image of its tracks leaving the Ubajara site in Gale Crater, where siderite was later discovered. (Credit: NASA/JPL-Caltech/MSSS)
As discussed in a new study led by Benjamin Tutolo of the University of Calgary in Canada, data collected from several of Curiosity’s drill sites in Gale Crater have shown the presence of siderite. Siderite is an iron carbonate mineral that exists within the sulfate-rich rocky layers of Mount Sharp, the 5,500 m tall mountain at the center of the crater that Curiosity is climbing.
“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,” Tutolo said.
Curiosity’s drill is used by planetary scientists to further study the chemical and mineral composition of the red planet. By drilling three to four centimeter holes into the Martian surface, Curiosity collects powdered rock samples and drops them into its Chemistry and Mineralogy (CheMin) instrument.
Once deposited into CheMin, the instrument uses X-ray diffraction to analyze the dust and soil samples. The results from CheMin’s analysis are then sent back to Earth, where scientists at NASA’s Johnson Space Center Astromaterials Research and Exploration Science (ARES) division further analyze the data.
“Drilling through the layered Martian surface is like going through a history book. 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,” said NASA Ames research scientist Thomas Bristow, who served as a co-author of the paper.
Curiosity drills into rock on the surface of Mars. (Credit: NASA/JPL-Caltech/MSSS)
The discovery of siderite within the slopes of Mount Sharp suggests that other, non-carbonate materials may mask carbonate minerals on Mars in infrared satellite analysis. While other sulfate-rich layers on the surface may contain carbonates like siderite, the amount of carbon dioxide stored within them would be much less than the amount needed for a thicker atmosphere to support liquid water. Thus, the rest of the carbon dioxide needed to support the existence of this ancient atmosphere must be hidden in deposits elsewhere on the Martian surface or lost to space over time.
To confirm where the rest of Mars’ surface carbon dioxide is hidden, scientists will need to send more missions to sulfate-rich areas on the Martian surface. Furthermore, continued analysis of these regions using orbital data could prove useful in solving the mystery of Mars’ once-thick atmosphere.
I found a clue to one of Mars’ many mysteries!
There's strong evidence the planet had liquid water billions of years ago, suggesting a carbon-rich atmosphere. But where did it all go? My CheMin instrument found a mineral that may help answer that. https://t.co/q1RFfet9V1 pic.twitter.com/pSeAMZssrX
— Curiosity Rover (@MarsCuriosity) April 17, 2025
While Curiosity’s discovery of siderite doesn’t explicitly confirm the past existence of a thick carbon-rich atmosphere, it brings planetary scientists one step closer to understanding ancient Mars and how a thick atmosphere can dwindle to the thin Martian atmosphere of today.
Curiosity landed on Mars in 2012 and has been roving around Gale Crater and the slopes of Mount Sharp ever since. To date, Curiosity has driven 34.59 km across the Martian surface, exploring the Aeolis Palus region of Gale Crater before turning and beginning its climb up Mount Sharp in September 2014. The rover recently left the Gediz Vallis channel on the side of the mountain and is now driving through a new valley.
Curiosity most recently made headlines in March when it was announced that the rover had detected the largest organic molecules to date on the red planet. The organic molecules discovered are thought to be fragments of fatty acids — one of the many organic molecules on Earth that serve as chemical building blocks for life.
Tutolo et al.’s study was recently published in the journal Science on April 17.
(Lead image: Curiosity takes a selfie while examining rocks on the Martian surface. Credit: NASA/JPL-Caltech/MSSS)
