In 2007, satellites detected something extraordinary over the eastern Atlantic Ocean: Earth’s gravity field developed a massive, continent-scale disturbance before returning to normal. This event, unnoticed on the surface, was revealed years later through data from the Gravity Recovery and Climate Experiment (GRACE), a NASA-DLR satellite mission that operated between 2002 and 2017. GRACE was designed to measure subtle changes in Earth’s gravity by monitoring the precise distance between two orbiting satellites. Variations in that distance reflect underlying shifts in mass distribution, from melting glaciers to groundwater depletion. However, what researchers uncovered in this case could not be explained by familiar surface processes.
The anomaly was first identified by a team led by geophysicist Charlotte Gaugne Gouranton of Paris City University. Analyzing GRACE data from 2006 to 2008, they discovered a large dipole pattern peaking in January 2007. This pattern extended over 7,000 kilometers, with a band of stronger gravity next to a region of weaker gravity. Such a signal suggested not simple addition or removal of mass, but rather a major redistribution occurring deep within the planet. What made this even more compelling was its timing: the gravity anomaly coincided with a “geomagnetic jerk,” a sudden shift in Earth’s magnetic field, recorded in the same region. Geomagnetic jerks are thought to be linked to processes in or near the liquid outer core, raising the possibility of a shared origin.
To rule out simpler explanations, the team tested whether surface processes—such as large-scale ocean movement or groundwater changes—could account for the signal. Their models showed this was impossible. The magnitude, location, and timing of the anomaly could not be reconciled with any known surface mass changes. The amount of water needed to generate the observed effect would have been physically unrealistic. With these possibilities eliminated, the researchers turned their focus inward, toward the planet’s deep mantle.
At roughly 3,000 kilometers beneath Earth’s surface, near the core-mantle boundary, exists extreme pressure and temperature where the mineral bridgmanite ((Mg,Fe)SiO₃) dominates. Under such conditions, bridgmanite can shift from a perovskite structure into a post-perovskite structure. This phase transition alters the mineral’s density, rapidly redistributing mass. Such a transformation could generate a signal like the one recorded by GRACE and may also explain the simultaneous geomagnetic jerk. Essentially, a sudden reconfiguration of material at the base of the mantle could ripple outward as both a gravity anomaly and a magnetic disturbance.
Intriguingly, seismic studies have also identified strange “blobs” of anomalous material near Earth’s core. The location of the 2007 event appears close to one of these features, suggesting they may be linked. If so, this would provide a rare observational window into processes that usually remain hidden deep inside our planet.
The researchers caution that their findings are preliminary and require further validation. Still, their work highlights the potential of satellite gravimetry to reveal not only surface water changes but also profound internal dynamics of Earth. The discovery of the 2007 gravity anomaly raises important questions: How often do such mass redistributions occur? Are they tied to larger cycles of mantle and core evolution? And what do they tell us about the stability of Earth’s interior over geological timescales? Answering these will deepen our understanding of the hidden forces shaping our planet.