Mars may appear spherical, yet it is actually a triaxial ellipsoid. Unlike the other rocky planets in our solar system, which resemble rugby balls, Mars varies in size along all three axes.
This is most apparent in the notable bulge of the Tharsis rise region and the contrasting region known as Sirtis Major.
Astronomer Dr. Michael Efroysky of the US Navy Observatory recently proposed that this peculiar shape may be attributed to the absence of an ancient moon on Mars.
The moon, named Nerio after the Roman goddess of war, who was associated with Mars, influenced the shape of the planet through tidal forces, similar to the oceans here on Earth.
However, once Mars cooled down, its deformed shape became permanently fixed.
Nerio’s tidal stress weakened the elevated regions of Mars, facilitating the impact of geological processes such as internal convection, structural shifts, and volcanic activity, all of which contributed to Mars’ asymmetrical shape.
Researchers propose that, in synchronous orbit around Mars, Nerio—being less than a third of Earth’s mass—could easily have formed the planet’s initial triaxial shape. The equatorial bulge would have been even more pronounced if Nerio had existed during the planet’s magma ocean phase.
Currently, Mars lacks such a moon, having only the small moons Deimos and Phobos. At some point, Nerio was either destroyed by another large body or pulled away by gravitational forces.
This article answers the question posed by Otto Sykes in an email: “Why does Mars have such a strange shape?”
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