What is the Martian equivalent of Earth's geoid called?

The Martian equivalent of Earth’s geoid is called the areoid. It is a gravity-based reference surface used to describe elevations on Mars, analogous to how Earth’s geoid approximates global mean sea level.

Mars has no oceans providing a natural sea-level datum, so planetary scientists define a zero-elevation reference using the planet’s gravitational and rotational fields. The areoid is therefore not simply Mars’s physical surface or a smooth geometric ellipsoid; it reflects variations in mass beneath the crust and the planet’s shape.

The name follows the planetary prefix areo-, derived from Ares, the Greek counterpart of the Roman god Mars. Modern Martian topographic maps, including datasets based on the Mars Orbiter Laser Altimeter, measure terrain height relative to this reference surface.

A common mix-up is “geoid,” which is Earth-specific in ordinary usage, or “ellipsoid,” which describes a mathematical approximation of a planet’s overall shape. The areoid is the more physically meaningful, gravity-based datum.