Martian atmospheric photochemistry and composition during periods of low obliquity

Abstract

During periods of low obliquity, previous work has shown that martian CO 2 partial pressures decreased to 0.1 mbar; CO 2 partial pressures decreased to 0.02 mbar prior to the formation of the Tharsis bulge. The permanent polar caps act as a cold trap and projected global average water vapor abundances drop to possibly as low as 10 −5 precipitable µm. As a result, the odd hydrogen catalytic cycle would not be effective at recombining CO and O back into CO 2 , and as much as 0.12 mbar of CO and 0.06 mbar of O 2 could exist. These increased abundances would radically affect surface oxidation, change the lower atmospheric thermal structure, and completely alter the upper atmosphere.