Huge Gravity Anomaly Near Africa

A major gravitational anomaly off the west coast of Africa appears to have changed on an unusually fast timescale—within about two years (2006–2008)—and it lines up with a simultaneous magnetic-field anomaly. The finding matters because it points to a dynamic process deep inside Earth, not a slow, millions-of-years geological event, and it shows how satellite gravity measurements can detect rapid shifts in the planet’s interior.

Researchers used data from the GRACE satellite mission, a joint effort between NASA and the German Aerospace Centre. GRACE flew two satellites in tandem from 2002 to 2017, separated by a few hundred kilometers, exchanging extremely precise microwave signals. By tracking tiny changes in the distance between the satellites, scientists inferred variations in Earth’s gravitational field with micrometer-level sensitivity over hundreds of kilometers. In the African offshore region, the gravity signal didn’t just get stronger or weaker—it changed faster from one area to the next, then stopped two years later.

The anomaly is also large in geographic extent: it stretches roughly 7,000 kilometers in the north–south direction, comparable to the distance between London and Chicago. That scale, combined with the short duration, makes the event stand out among known gravity anomalies. The transcript notes that geophysicists typically expect gravity-related changes to evolve over far longer periods.

Complicating the picture, the gravity anomaly coincided with an earlier-reported anomaly in Earth’s magnetic field in the same region and time window. Whether the two signals share a cause remains unclear, but the overlap raises the possibility of a common driver. The most widely accepted explanation for magnetic-field changes in general involves processes in Earth’s core, where moving conductive material generates and reshapes the geomagnetic field.

To explain the gravity data, the authors of the new paper considered and rejected a straightforward ocean-current mechanism. Because the anomaly was measured over ocean waters, shifting currents could in principle redistribute mass and alter local gravity. But the proposed current-driven effects didn’t match the observed shape and size.

Instead, the preferred explanation centers on the mantle. Roughly 3,000 kilometers down, a large region of rock may have begun to move upward in an “upwelling.” As the material rose, pressure dropped enough to trigger a phase transition in bridgmanite, a dense mineral in the perovskite family (also associated with materials used in solar panels). The phase change increased density, producing the sudden gravity shift. As the upwelling continued upward and spread out, the density contrast would dilute, allowing the gravity anomaly to fade—consistent with the signal appearing and then disappearing after about two years.

The transcript closes by emphasizing a practical tension: Earth’s gravity can now be measured with extraordinary precision, yet scientists still lack a way to directly “open” the planet and verify what’s happening inside. The event is not described as immediately dangerous, but it underscores how much of Earth’s interior remains observationally indirect—and how quickly it can, at least sometimes, change.