A long-lost moon, possibly named Nerio, could explain Mars’ unique shape and extreme terrain, including the Tharsis bulge and other highland regions. Michael Efroimsky of the U.S. Naval Observatory suggests that this moon’s significant mass altered Mars’ shape by raising tides in its magma oceans, similar to how Earth’s moon affects ocean tides. Mars cooled quickly, locking these tidal bulges into its form. This theory is detailed in a paper submitted to the Journal of Geophysical Research: Planets and available on arXiv.