A Synchronous Moon as a Possible Cause of Mars' Initial Triaxiality

Abstract

The paper addresses the possibility of a young Mars having had a massive moon, which synchronized the rotation of Mars, and gave Mars an initial asymmetric triaxiality to be later boosted by geological processes. It turns out that a moon of less than a third of the lunar mass was capable of producing a sufficient initial triaxiality. The asymmetry of the initial tidal shape of the equator depends on timing: the initial asymmetry is much stronger if the synchronous moon shows up already at the magma-ocean stage. From the moment of synchronization of Mars' rotation with the moon's orbital motion, and until the moon was eliminated (as one possibility, by an impact in the beginning of the Late Heavy Bombardment), the moon was sustaining an early value of Mars' rotation rate.