Carbon dioxide: Adsorption on palagonite and partitioning in the Martian regolith

We report new CO₂ adsorption measurements on palagonites. These results are used together with earlier results on basalt and nontronite adsorption to derive a “generic” relationship which is valid to within a factor of 3 for likely mixtures of basalt and weathering products of basalt. The relationship involves only t, P_CO2, and the specific surface area, and is relatively insensitive to mineralogy. It is used to predict the distribution and exchange of CO₂ on Mars. We conclude: (1) One to two orders of magnitude more CO₂ is adsorbed on the regolith than is present in the atmosphere and cap. (2) Nonetheless, most of the initially degassed CO₂ must have been lost to space or must be present as carbonates, especially if there was enough degassed CO₂ to provide a significant early greenhouse effect. (3) Given the derived relationship, the CO₂ vapor pressure curve, and the constraint that the system exhibits the current P_CO2 at the current obliquity, it is possible to predict approximately the atmospheric pressure at any obliquity (with or without a cap) without knowing the total available CO₂ inventory, the regolith mass, the regolith distribution, or its mineralogy, any better than those parameters are currently known.