Oxidation of CO on surface hematite in high CO2 atmospheres

Abstract We propose a mechanism for the oxidation of gaseous CO into CO 2 occurring on the surface mineral hematite (Fe 2 O 3 (s)) in hot, CO 2 -rich planetary atmospheres, such as Venus. This mechanism is likely to constitute an important source of tropospheric CO 2 on Venus and could at least partly address the CO 2 stability problem in Venus’ stratosphere, since our results suggest that atmospheric CO 2 is produced from CO oxidation via surface hematite at a rate of 0.4 petagrammes (Pg) CO 2 per (Earth) year on Venus which is about 45% of the mass loss of CO 2 via photolysis in the Venusian stratosphere. We also investigated CO oxidation via the hematite mechanism for a range of planetary scenarios and found that modern Earth and Mars are probably too cold for the mechanism to be important because the rate-limiting step, involving CO(g) reacting onto the hematite surface, proceeds much slower at lower temperatures. The mechanism may feature on extrasolar planets such as Gliese 581c or CoRoT-7b assuming they can maintain solid surface hematite which, e.g. starts to melt above about 1200 K. The mechanism may also be important for hot Hadean-type environments and for the emerging class of hot Super-Earths with planetary surface temperatures between about 600 and 900 K.