Oxidation of CO on surface hematite in high CO2 atmospheres

TL;DR

This paper proposes a surface hematite-catalyzed mechanism for CO oxidation to CO2 in high CO2 atmospheres, potentially explaining CO2 sources on Venus and relevance for hot exoplanets.

Contribution

It introduces a new surface chemistry mechanism for CO oxidation on hematite, relevant to planetary atmospheres and exoplanets, with quantitative estimates for Venus.

Findings

Hematite-mediated CO oxidation could produce 0.4 Pg CO2/year on Venus.

The mechanism is ineffective on Earth and Mars due to low temperatures.

Potential significance for hot exoplanets with surface temperatures 600-900K.

Abstract

We propose a mechanism for the oxidation of gaseous CO into CO2 occurring on the surface mineral hematite (Fe2O3(s)) in hot, CO2-rich planetary atmospheres, such as Venus. This mechanism is likely to constitute an important source of tropospheric CO2 on Venus and could at least partly address the CO2 stability problem in Venus' stratosphere, since our results suggest that atmospheric CO2 is produced from CO oxidation via surface hematite at a rate of 0.4 Petagrammes (Pg) CO2 per (Earth) year on Venus which is about 45% of the mass loss of CO2 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 1200K. 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 600-900K.