The evolution of CO2 on Mars

At the surface, the atmosphere of Mars contains approximately 95.3 percent CO2 by volume. At the Viking Lander 1 (VL1) site, the total surface pressure varied with the season between about 6.89 and 8.94 mbar. Questions related to the observed CO2 pressure on Mars are explored. Several published estimates of the total amount of CO2 outgassed over the history of Mars, varying between 140 and 3000 mbar, are shown in a table. It is pointed out that the study of likely reservoirs for outgassed CO2 has focused mainly on the polar caps and regolith. Constraints on the formation of transitory pockets of moist soil are discussed, taking into account heat requirements, supply of water, and constraints related to pressure. Attention is also given to chemical considerations, implications for the current status of CO2 reservoirs, and scenarios for the evolution of CO2 pressure.