Models suggest feldspar-rich rock explains Mars' calcium/iron carbonates

By the Everything Space news desk · 17 Sep 2026 · written from the sources below

Image: Phys.org

New geochemical simulations point to hidden underground carbonate deposits that could hold much of Mars' missing ancient carbon dioxide.

Mars has far less surface carbonate than climate models predict for a planet that once had a thick, carbon dioxide-rich atmosphere, leaving scientists to wonder where that carbon went. A new study using thermochemical simulations offers a possible explanation tied to the type of rock that ancient water once flowed through.

Researchers built computer models simulating water moving through columns of rock under cold, carbon dioxide-rich conditions similar to early Mars. They tested two rock types: the iron- and magnesium-rich mafic rock common across the planet, and feldspar-rich rock, which contains more calcium, sodium and aluminum and has been increasingly spotted by orbiters and rovers.

The simulations found that feldspar-rich rock reliably produces calcium- and iron-rich carbonates across a wide range of conditions, while mafic rock only generates that same type of carbonate during brief periods of water-rock interaction before shifting toward magnesium-rich carbonates instead. This gives researchers a clearer way to interpret surface observations, since calcium/iron-rich carbonates found without magnesium-rich olivine nearby likely point to a feldspar-rich source rock.

The models also showed that groundwater percolating downward through rock was much better at forming carbonates than standing water, but it also tended to dissolve carbonates near the surface and reform them deeper underground. That process could help explain why the Martian surface looks carbonate-poor even if significant stores of carbonate, and the carbon dioxide locked inside them, exist below ground.

The findings suggest that the split between calcium/iron-rich and magnesium-rich carbonates on Mars reflects not just past climate and water conditions but the composition of the rock those waters passed through. The authors suggest that feldspar-rich terrain and subsurface drilling could be promising targets for future missions searching for buried evidence of the planet's wetter past.

Written in Everything Space’s own words by our news-desk model from the sources above, and checked against them in code: every number in this report appears in its sources, and no sentence is copied from them.