New findings from NASA’s Curiosity rover suggest that Mars once hosted a dynamic carbon cycle similar to Earth’s, shedding light on the planet’s ancient climate and atmospheric conditions. In a breakthrough study published in Science, researchers analyzed sediments from Gale Crater and identified substantial deposits of the iron carbonate mineral siderite—marking direct evidence that carbon dioxide was sequestered in Martian rock billions of years ago.

Discovery of Carbonates in Martian Sediments

Scientists examined an 89-meter stratigraphic section within Gale Crater using Curiosity’s onboard Chemistry and Mineralogy (CheMin) instrument, which confirmed the presence of siderite in concentrations ranging from 4.8% to 10.5% by weight. The discovery is significant because carbonates on Mars have been scarce despite models predicting their widespread formation through reactions between liquid water and atmospheric CO₂.

Researchers believe these carbonates formed under water-limited conditions, driven by evaporation and interactions between rock and liquid water. This suggests that ancient Mars had a partially closed carbon cycle, meaning some of the previously sequestered CO₂ could have been released back into the atmosphere.

Implications for Mars’ Ancient Atmosphere

Curiosity’s analysis supports the theory that Mars had a thicker atmosphere in the past, potentially containing tens to hundreds of millibars of CO₂. These findings align with climate models that require significant greenhouse gas concentrations to allow liquid water to remain stable on the surface.

The research team estimates that globally deposited carbonate-bearing strata could have trapped between 2.6 and 36 millibars of atmospheric CO₂—equivalent to several times Mars’ current atmospheric pressure. The presence of iron oxyhydroxides within these deposits further indicates that atmospheric carbon could have been re-released over time, creating a dynamic exchange similar to Earth’s carbon cycle.

The Role of Evaporation and Chemical Sedimentation

Scientists propose that evaporation played a crucial role in triggering carbonate formation. As Martian lakes dried up, chemical reactions facilitated the deposition of siderite alongside sulfate minerals. This process mirrors similar mechanisms found on Earth, where evaporative concentration in closed-basin lakes leads to mineral sequestration.

Over time, post-depositional alterations—possibly linked to sulfuric acid infiltration—transformed some of the original carbonates into iron-rich minerals, reintroducing CO₂ into the atmosphere. This finding suggests that Mars’ carbon cycle was not static but evolved through geological processes.

Looking Ahead

The discovery of Mars’ ancient carbon cycle has profound implications for understanding the planet’s habitability and potential for past life. If carbonate deposits are more widespread than previously detected, future Mars missions could target similar strata to reconstruct the planet’s environmental history.

NASA’s ongoing exploration, including the upcoming Mars Sample Return mission, may allow scientists to analyze these carbonates directly on Earth, unlocking further insights into the planet’s atmospheric evolution.

These findings reinforce the idea that Mars was once a more Earth-like world, with dynamic interactions between its atmosphere, water, and rocky crust—bringing scientists one step closer to unraveling the mysteries of the Red Planet.

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