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The scientists built a model of the polar wander, accounting for factors such as reservoirs filling because of new dams and ice sheets melting, to see how well they explained the polar movements observed between 1993 and 2010.

In the paper Shuai and his co-authors note the ice’s patchiness may be due to a hypothesized phenomenon called “true polar wander,” in which the orientation of the moon’s axis of spin shifts over long periods of time.

However, surface loading from the oceans can drive polar wander only if Tharsis formed far from the equator10, and most evidence indicates that Tharsis formed near the equator11,12,13,14,15, meaning that there is no current explanation for the shorelines’ deviation from an equipotential that is consistent with our geophysical understanding of Mars.

The shorelines’ deviation from a constant elevation can be explained by true polar wander occurring after the formation of Tharsis10, a volcanic province that dominates the gravity and topography of Mars.

Rouby, H., Greff-Lefftz, M. & Besse, J. Rotational bulge and one plume convection pattern: influence on Martian true polar wander.