The geoid: Earth is not a sphere, it's an irregular potato

The geoid: Earth is not a sphere, it's an irregular potato

Have you ever wondered why world maps are always distorted? The answer lies in the geoid, the real shape of our planet, which is far from being a perfect sphere. It is an irregular surface, determined by the gravitational field, with bulges and depressions of up to ±100 metres. This is no academic curiosity: it affects GPS navigation and the measurement of altitudes.

What the geoid is and why it isn't a sphere

The geoid is the surface the oceans would adopt under the sole influence of gravity and the Earth's rotation, with no tides or winds, hypothetically extended beneath the continents. As an equipotential surface of gravity, the perpendicular force varies according to the distribution of mass: mountains and ocean trenches generate anomalies. So the planet doesn't look like a marble, but rather like a deformed potato.

From spheroid to potato: how it is measured

Technically, the Earth approximates a reference ellipsoid (flattened at the poles), but the geoid refines that model with local irregularities. Satellites such as GRACE and GOCE have mapped these variations with centimetre-level precision. The result is a three-dimensional model showing where gravity is stronger or weaker, with direct implications for geodesy and oceanography.

The fun fact: if you remove the atmosphere and the water, the underlying shape is even more amorphous, almost unrecognisable. But you don't need to be a conspiracy theorist to accept that the Earth isn't round: it's a geoid. And yes, some people joke about "potato-earthism", but science backs it up. Draw your own conclusions about whether you prefer a perfect sphere or a lumpy potato.