  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.
