A synchronous moon as a possible cause of Mars' initial triaxiality

TL;DR

This paper explores the hypothesis that a young Mars with a massive moon could have developed initial triaxiality through synchronous rotation, influencing its early geological and rotational history.

Contribution

It demonstrates that a relatively small moon could induce initial triaxiality in Mars, with the effect depending on the timing of moon formation during Mars' magma ocean stage.

Findings

A moon less than a third of lunar mass can produce sufficient initial triaxiality.

Initial asymmetry is stronger if the moon formed during Mars' magma-ocean stage.

The moon's presence affected Mars' early rotation rate until its elimination.

Abstract

The paper addresses the possibility of a young Mars having had a massive moon, which synchronised 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 synchronisation 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 LHB), the moon was sustaining an early value of Mars' rotation rate.