NASA's Curiosity rover has uncovered new geological evidence pointing to a once-active carbon cycle on ancient Mars, offering a compelling window into the Red Planet's former potential to support life.
An artist's concept portrays a NASA Mars Exploration Rover on the surface of Mars.
Credit: NASA/JPL/Cornell University, Maas Digital LLC
The breakthrough findings, published in Science, center on the discovery of siderite—an iron carbonate mineral—within sulfate-rich rock layers inside Gale Crater’s Mount Sharp. This mineral, which forms in carbon dioxide-rich environments, suggests Mars once had a thicker atmosphere capable of sustaining liquid water.
Dr. Ben Tutolo, a geoscientist at the University of Calgary and member of the Curiosity science team, played a central role in the research. His work focuses on climate shifts and the question of early Martian habitability.
“The discovery of large carbon deposits in Gale Crater is both surprising and significant,” said Tutolo. “It fundamentally changes how we understand Mars’ geological and atmospheric history.”
While scientists had long theorized that a dense, CO2-laden atmosphere once warmed early Mars, direct evidence of extensive carbonates has been limited—until now. Curiosity’s detection of siderite
across three separate drill sites supports the idea of a functioning carbon cycle billions of years ago.
Schematic illustration of proposed carbon cycle on early Mars.
Evaporation of water (pink shading) from subsurface pore spaces initially deposits siderite, which sequesters atmospheric CO2 (black downward arrow). Increasing levels of evaporation deposit Ca-sulfate and Mg-sulfate minerals. Wind-blown (eolian) sedimentation at the ground surface (gray dots) moves the location of evaporation and chemical sedimentation upward with time. After some time (white arrow), infiltration of siderite-undersaturated fluids (yellow shading) partially destroys the previously precipitated siderite, forming Fe-oxyhydroxides and releasing previously sequestered CO2 back into the atmosphere (black upward arrow).
The rover’s findings also indicate a dramatic environmental transformation: from a potentially habitable world with flowing water to the cold, barren desert we see today. As atmospheric CO2 began to bind into rock as minerals like siderite, Mars likely lost much of its greenhouse effect, accelerating its shift to an inhospitable state.
Since its landing in 2012, Curiosity has traveled more than 34 kilometers, methodically analyzing rock formations for clues to the planet’s past. Its latest discoveries strengthen models suggesting ancient Mars was once capable of supporting life.
“This tells us the planet was not only habitable, but that the mechanisms that made it so were similar to Earth’s,” Tutolo noted. “But as CO2 began precipitating into minerals, Mars may have lost its ability to stay warm.”
The findings raise key questions about how much atmospheric carbon dioxide was sequestered into rock—and whether this natural process played a leading role in Mars' climate collapse.
Tutolo, who also studies carbon mineralization on Earth, said the parallels between Mars and Earth have real implications for climate science here at home.
“Understanding how these minerals formed on Mars helps us explore how we might use similar processes to capture carbon on Earth,” he explained. “It also reminds us how fragile planetary habitability really is.”
He added, “The fact that Earth has remained habitable for over four billion years is extraordinary. Mars wasn’t so lucky.”
NASA is already eyeing future missions to investigate more sulfate-rich terrains, which could shed further light on the role of carbonates in Mars’ ancient atmosphere—and bring us one step closer to understanding the full story of its lost habitability.
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