Scientists have identified a rare geological shift near the boundary between Earth’s core and mantle after satellite data revealed an unexplained change in the planet’s gravitational field.

The change, which occurred between 2006 and 2008, was detected only recently during an analysis of data from a pair of satellites that once measured variations in Earth’s gravity. Researchers believe the shift may have been triggered when the structure of some rocks near the boundary between Earth’s core and mantle transformed, becoming denser

The findings, published in Geophysical Research Letters, could help explain connections between Earth’s various layers, which influence earthquakes, the planet’s magnetic field, among others.

The discovery was detected using data from a pair of US–German satellites known as the Gravity Recovery and Climate Experiment (GRACE), which orbited Earth between 2002 and 2017. The twin satellites flew in tandem, measuring changes in distance between them caused by variations in Earth’s gravity field.

GRACE has often been used to measure movements of water and ice, but the data showed a signal peaking around 2007 off Africa’s Atlantic coast that could not be explained by surface changes.

One explanation is that perovskite, a mineral found in rocks near the bottom of the mantle, changed structure under extreme pressure, making the rocks denser. This could have caused a chain of shifts extending to the core–mantle boundary, which may have deformed by about 10 centimetres. Such movement might also explain magnetic anomalies recorded in the same region around 2007.