Britannica Sources used in this answer

How do irregularities in Earth’s gravity field change a satellite’s orbit?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Diagram showing the deflection of the vertical from the geoid to the ellipsoid or spheroid, with labeled lines for geoid, spheroid, rock surface, ocean, and geoid height in a geology context. — geoid Deflection of the vertical from the geoid to the spheroid.

Irregularities in Earth’s gravity field, caused by the planet's non-spherical mass distribution, exert forces on satellites that perturb their orbits from the simple elliptical paths described by Kepler’s laws of planetary motion.1

The most significant irregularity is Earth’s equatorial bulge, which creates a torque that causes the satellite’s orbital plane to precess. Additionally, variations in mass density within the mantle and the distribution of continents and oceans create gravitational anomalies that lead to further orbital deviations.213

For geostationary satellites, these gravitational irregularities can destabilize their positions, causing them to drift unless they use onboard propulsion to compensate. By observing these precise orbital perturbations, scientists can map the geoid—the surface of equal gravitational potential—and gain insights into Earth’s internal structure, such as mantle convection and plate tectonics.213