NASA’s Curiosity rover has detected signs of significant amounts of carbon dioxide locked within the Martian crust, potentially shedding light on the Red Planet’s ancient carbon cycle and its past habitability.
Though Mars is now cold and barren, geological features such as dry riverbeds and sediment layers suggest it once hosted lakes and flowing water. These features imply that the planet once had a much thicker atmosphere rich in carbon dioxide, which would have created warmer conditions suitable for liquid water. Yet, scientists have long puzzled over the absence of expected levels of carbonate minerals—typically formed through interactions between water, carbon dioxide, and rock—in previously analyzed Martian samples.
Crater Investigations
“The discovery of large carbon deposits in Gale Crater represents both a surprising and important breakthrough in our understanding of the geologic and atmospheric evolution of Mars,” says Dr. Ben Tutolo of the University of Calgary and the NASA Mars Science Laboratory Curiosity rover.
Tutolo led the research team in examining an ancient lake bed in Gale Crater. Between 2022 and 2023, Curiosity drilled four samples at varying depths to investigate the transition from Mars’s formerly wet environment to its current arid state, using its onboard X-ray diffractometer.
Mars’s Surprising Carbonate Deposits
“The abundance of highly soluble salts in these rocks and similar deposits mapped over much of Mars has been used as evidence of the ‘great drying’ of Mars during its dramatic shift from a warm and wet early Mars to its current, cold and dry state,” explains Tutolo.
Earlier satellite observations suggested that these layers lacked carbonates, contradicting predictions about Mars’s wetter past. However, Tutolo’s team identified unexpectedly high concentrations—between 5% and 10% by weight—of iron carbonates and siderite in magnesium sulfate-rich deposits. Based on their chemistry and location, the researchers believe that interactions between water and rock, combined with evaporation, trapped atmospheric carbon dioxide in the form of sedimentary minerals.
How Much Carbon Exists on the Red Planet?
“The question looking forward is how much of this CO₂ from the atmosphere was actually sequestered? Was that potentially a reason we began to lose habitability because we no longer can warm the planet because there was only so much CO₂ in the atmosphere?” Tutolo questions.
The findings suggest that Mars may contain a vast, previously undetected carbon reservoir. However, determining whether these deposits are isolated or common across the planet will require additional exploration. Some carbonate materials appear to have broken down over time, possibly releasing carbon dioxide back into the atmosphere—indicating a complex, long-term carbon cycle.
“It tells us that the planet was habitable and that the models for habitability are correct,” Tutolo adds. “The broader implications are the planet was habitable up until this time, but then starts to precipitate siderite.”
Continuing Habitability Research
Confirming the presence of an ancient carbon cycle would be a major step toward verifying that Mars once supported life-friendly conditions. According to NASA, future studies of Martian carbonates could provide critical insights into how the planet’s atmosphere diminished over time.
“It tells us the mechanisms of making these minerals from the salts on Mars and how we can do it here,” Tutolo says. “It also tells us that habitability is a very fragile thing.”
“The most remarkable thing about Earth is that it’s habitable and it has been for at least four billion years,” he concludes. “Something happened to Mars that didn’t happen to Earth.”
The new paper, “Carbonates Identified by the Curiosity Rover Indicate a Carbon Cycle Operated on Ancient Mars” appeared on April 18, 2025, in Science.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.