Mineral alteration in water-saturated liquid CO2 on early Mars

Geomorphological and mineralogical evidence is consistent with aqueous activity on ancient Mars, yet explaining the presence of substantial liquid water on early Mars remains challenging. Another fluid, liquid CO₂, was probably present during Martian history, at least in the subsurface, and could even have been stable at the surface under a sufficiently dense CO₂-rich early atmosphere. Liquid CO₂ flows have been proposed as an alternative to water to explain morphological features, but it is widely accepted that water is the fluid responsible for mineral alteration. Interestingly, however, experimental research on geologic sequestration on Earth has revealed a surprising degree of chemical reactivity between CO₂ fluid and minerals if the fluid is water-saturated, as it would probably have been on Mars. The resulting alteration products — carbonates, phyllosilicates and possibly sulfates — are consistent with minerals found on Mars today. We therefore propose that the formation of some of the aqueous mineral alteration observed on the Martian surface may have been mediated by liquid CO₂. Further laboratory investigations are needed to test this hypothesis.