Chaotic obliquity and the nature of the Martian climate

Recent calculations of the Martian obliquity suggest that it varies chaotically on timescales longer than about 10 7 years and varies between about 0 and 60°. We examine the seasonal water behavior at obliquities between 40 and 60°. Up to several tens of centimeters of water may sublime from the polar caps each year, and possibly move to the equator, where it is more stable. CO 2 frost and CO 2 ‐H 2 O clathrate hydrate are stable in the polar deposits below a few tens of meters depth, so that the polar cap could contain a significant CO 2 reservoir. If CO 2 is present, it could be left over from the early history of Mars; also, it could be released into the atmosphere during periods of high obliquity, causing occasional periods of more‐clement climate.