Early Mars Carbonates: A Chemical Mystery

Earth's neighbor, Mars, has long been known to have once hosted extensive water-rock interactions under a carbon dioxide-rich atmosphere. However, carbonate minerals, which are common signs of such interactions, are surprisingly scarce on the Martian surface. Some scientists suggest that these carbonates might have been destroyed over time, especially due to changes in the atmosphere. One major shift was the release of sulfur dioxide (SO₂) from volcanic activities, which could have altered the chemical balance. But until now, no study has thoroughly investigated how common carbonates like calcium, magnesium, and iron carbonates react to high levels of SO₂.

Researchers recently conducted experiments to see what happens when these carbonates are exposed to 0. 8 bar of SO₂ in different environments. They found that in both moderately and strongly oxidizing conditions (mixing SO₂ with water, and SO₂ with water and hydrogen peroxide, respectively), the carbonates broke down. In these reactions, the final products were mainly sulfates, except for calcium carbonate, which turned into calcium sulfite, a compound known as hannebachite, in moderately oxidizing conditions. These findings suggest that early Martian carbonates would have been quickly replaced by sulfates and possibly sulfites, especially if calcium was abundant. This change could have occurred due to major volcanic events like those linked to the formation of the Tharsis rise.

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