A striking image released by NASA has prompted widespread discussion by depicting Earth in a form that defies the familiar globe. The visual quickly gained traction on social media. Its pronounced irregularities have drawn comparisons to a potato and fueled speculation about Earth's true shape. It is a scientific model, not a photograph or a depiction of Earth's physical surface.
The image represents the geoid, a gravity-defined reference surface that approximates global mean sea level. Unlike a smooth reference ellipsoid, the geoid reflects variations in Earth's gravitational potential caused by mass distributed unevenly within Earth and beneath its oceans. It is not the ocean's actual surface, which is also shaped by tides and other ocean dynamics. NASA has exaggerated the geoid's irregularities by a factor of 10,000 to make them visible. The underlying differences are only a few dozen metres, tiny beside Earth's roughly 6,400-kilometre radius.
NASA's GRACE and GRACE Follow-On (GRACE-FO) missions show how satellites can measure changes in Earth's gravity. Each mission uses two satellites flying in tandem. As the lead satellite passes over a region with greater mass, gravity slightly changes its motion, and instruments measure the resulting change in the distance between the pair. The satellites do not photograph the geoid. Scientists use their measurements to infer changes in mass distribution.
Launched in 2002 as a joint mission by NASA and the German Aerospace Center, GRACE began a record of satellite gravity observations that GRACE-FO later extended. NASA reports that the combined record spans more than two decades, with measurements from April 2002 through November 2025 used in its latest analysis of terrestrial water storage. Water and ice shift and accumulate, making their gains and losses detectable through changes in gravity. These observations help researchers track groundwater and ice, as well as changes in water stored on land and in the oceans.
The geoid helps geodesists define elevations and compare measurements against a consistent reference surface. Gravity-field models also support mapping and navigation by improving the link between satellite positioning, measured height and sea-level-based elevation. The model captures how gravity varies geographically: regions with more or denser mass exert stronger attraction, while lower-density structures exert weaker attraction. These variations are subtle, but accounting for them matters in precise Earth measurement and observation.
Earth itself is approximately an oblate spheroid, flattened at the poles and wider at the equator because of its rotation. The geoid is a different kind of representation: it describes a gravity-defined level surface rather than the planet's visible topography or overall geometric shape. NASA's gravity measurements provide a way to study mass redistribution and long-term changes in the Earth system. The familiar “potato” rendering makes otherwise minute gravitational differences easier to see.
