Satellites detected a strange gravity signal deep within earth

Almost twenty years ago, satellites orbiting high above Earth picked up a mysterious signal, a subtle but measurable shift in the planet’s gravitational field. Now, new research suggests that something extraordinary may have been happening deep inside the planet at that time.

Between 2006 and 2008, the GRACE satellites (Gravity Recovery and Climate Experiment), a joint mission between NASA and the German Aerospace Center, detected an unusual north–south–oriented gravity anomaly stretching nearly 7,000 kilometers, roughly the length of Africa.

The anomaly lasted for about two years, peaking in early 2007, and coincided with a sudden change in Earth’s magnetic field, known as a geomagnetic “jerk.” The overlap raised a fascinating question: could the two events be linked by a hidden process unfolding deep in the mantle, near the planet’s molten outer core?

A hidden shift in earth’s deep mantle

A team of geophysicists of France’s National Centre for Space Studies (CNES) believes so. In their paper, the researchers propose that the signal may have been caused by a phase transformation in magnesium silicate (MgSiO₃), a major component of the lower mantle (Geophysical Research Letters). Under extreme pressure, this mineral can shift from a perovskite to a post-perovskite structure, a change that could rapidly redistribute mass thousands of kilometers below the surface. Such a redistribution, though invisible to us, would subtly distort Earth’s gravitational and magnetic fields, just as the GRACE satellites observed.

The GRACE satellites, active from 2002 to 2017, orbited Earth in tandem, precisely measuring the distance between each other to detect tiny changes in gravity caused by variations in mass. While these shifts often reflect surface phenomena like ocean currents or melting ice, this anomaly pointed to something far deeper.

For researchers, it’s a reminder that Earth remains a dynamic, living system, constantly reshaping itself in ways we are only beginning to understand.