The effects of seasonal mass redistribution and interior structure on Length-of-Day variations of Mars

The effect of Mars’ interior structure, more precisely the influences of the size and the state of the core, on Length-of-Day variations (ΔLOD) is studied. We calculated the load Love numbers and the moments of inertia of the mantle and of the core for a set of models of Mars’ interior. It is shown that the current level of precision of LOD observations does not allow to deduce details of the Martian interior. Future measurements of ΔLOD must have an accuracy better than 2% to determine whether or not the core is liquid, and even better to constrain the core size. The effect of seasonal mass redistribution on ΔLOD is also investigated. Martian ΔLOD is a good indicator of global scale seasonal CO2 cycle. Planetary rotation data from the tracking of Viking and Pathfinder landers are compared with the recent seasonal mass deposition information from Mars Global Surveyor and Mars Odyssey missions. The results reveal the current difficulties in the accurate modelling of the Martian seasonal CO2 cycle.