Experimental simulations of the photodecomposition of carbonates and sulphates on Mars

Abstract

THERE is indirect spectroscopic evidence for the presence of sulphates and carbonates on the martian surface^1–5, and such minerals are also found in SNC meteorites⁶, which are thought to be of martian origin. But although carbonates are expected to be abundant in the martian regolith^7–9, attempts to detect them directly have been unsuccessful^10,11. Here we report laboratory studies of the decomposition of calcium carbonate and magnesium sulphate under ultraviolet irradiation, which mimic the conditions under which photodecomposition of surface minerals by solar ultraviolet light might occur on Mars. We find that, even for a low abundance6 of carbonate minerals in the martian regolith, the rate of CO₂ release due to photodecomposition is higher than the rate of CO₂ loss from the atmosphere by solar-wind-induced sputtering processes^12–15, making this process a potential net source of atmospheric CO₂ over time. SO₂ is also released from the sulphate, albeit more slowly. The rate of carbonate degradation is high enough to explain the apparent absence of these compounds at the martian surface.