Earth’s center is moving, and NASA just measured it

- Date:

- October 7, 2026

- Source:

- NASA

- Summary:

- Earth’s center of mass is constantly on the move, shifting by a few millimeters as enormous amounts of water, ice, and even air migrate around the planet with the seasons. NASA scientists have developed a more precise way to track these tiny swings using laser-ranging satellites, GPS data, and measurements of how water and ice deform Earth’s crust.

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Earth's center of mass does not stay perfectly still. As water, ice, and air move around the planet with the seasons, they redistribute enough weight to push the center of mass back and forth by fractions of an inch relative to Earth's geometric center.

NASA scientists carefully track this subtle motion because Earth's center of mass serves as an essential reference point for satellite navigation and measurements of surface elevation.

Researchers led by NASA's Jet Propulsion Laboratory in Southern California have now developed a method designed to measure these seasonal shifts with exceptional precision. Their technique and results are described in a new study published in Geophysical Journal International.

The research shows how major seasonal changes, including melting snow, moving ocean water, and dense winter air, redistribute enormous amounts of mass across Earth's surface.

Earth's Center Is Constantly Moving

Scientists have spent decades developing methods to define and locate Earth's center of mass using observations from space. The challenge is that the center does not remain in one fixed location.

If Earth behaved like a completely solid blue marble, its center of mass would line up with its geometric center. Instead, the planet responds to the shifting weight of water, ice, and the atmosphere. As those materials move, Earth's center of mass circles around its geometric center by as much as several millimeters.

Determining the exact size of that movement has proven difficult. The two most recent international estimates, produced in 2017 and 2023, differ by 0.27 inches (7 millimeters), roughly equivalent to the height of three nickels stacked together. That disagreement is nearly as large as the movement scientists are attempting to measure.

To narrow that uncertainty, JPL geoscientist Donald Argus led the development of a new approach that relies on extremely precise satellite tracking.

Gravity causes satellites to orbit around Earth's center of mass. As that center shifts, scientists can detect minute changes in the distances between orbiting satellites and tracking stations on the ground.

Satellites Help Pinpoint Earth's Center

Scientists have long used satellites to determine the location of Earth's center of mass. Two dense metal satellites launched in 1976 and 1992 were built specifically for that purpose.

The Laser Geodynamics Satellites (LAGEOS 1 and 2) resemble 900-pound (408-kilogram) disco balls covered with reflective prisms. Ground stations spread across more than 20 countries fire lasers at the satellites and precisely measure the returning signals.

One challenge with this method is that the laser tracking stations are not evenly distributed around the globe.

The new approach addresses that limitation in two ways. Researchers combine the laser measurements with GPS tracking and orbital information from several satellites in low Earth orbit, giving them a wider range of objects to follow. They also account for how the changing weight of water and ice bends Earth's crust, which means the ground stations themselves move slightly as the surface beneath them shifts.

Argus developed the technique with scientists from JPL's satellite orbit determination team, the University of Nevada, University of Montana, and the Helmholtz Centre for Geosciences in Germany.

"We're now estimating the size of the movement of Earth's mass center back and forth each year to be about half of what we believed it to be eight years ago," said Argus. "Our findings suggest that the mass of Earth's water and air moving between the hemispheres is smaller than previously thought."

Although the distances involved are tiny, their importance extends far beyond the laboratory.

Felix Landerer, one of the study's coauthors at JPL, noted that "while these movements might appear tiny, our modern world relies on extremely accurate positioning measurements. By unraveling and understanding the mechanisms that change reference systems, we can build better reference systems that ultimately benefit mapping and navigation -- from global shipping logistics to precision agriculture."

Snow, Rain, and Oceans Shift Earth's Balance

The researchers followed the seasonal movement of Earth's center of mass and traced it to three major sources: the oceans, the atmosphere, and continental water (made up of land ice, snow, lake and river water, soil moisture, and groundwater).

The effects change throughout the year as water and air accumulate in different parts of the world.

Snow across North America and Eurasia reaches its greatest accumulation in March. That added mass shifts Earth's center of mass about 3 millimeters toward the North Pole.

In April, the Amazon River basin reaches its seasonal maximum for rainwater, holding about 2,400 gigatons. That enormous concentration of water pulls Earth's center of mass 2.2 millimeters toward South America.

Another contribution arrives later in the year. Monsoon water in Southeast Asia peaks at 600 gigatons in November, six months after the Amazon maximum, and adds a smaller amount to the annual movement.

The Pacific Ocean Has an Outsized Influence

Ocean water also plays a major role in the seasonal shift.

From August through October, meltwater and rainfall add mass to the oceans, pushing Earth's center of mass toward the South Pacific Ocean.

Because the Pacific is so vast, changes in its mass can outweigh gains or losses in other ocean basins. Even so, seasonal changes in the Mediterranean, Red, North, Baltic, and Barents seas each make smaller contributions to the movement of Earth's center.

The atmosphere adds another layer to the cycle.

Researchers used a model created by the European Centre for Medium-Range Weather Forecasts to estimate how seasonal atmospheric changes alter Earth's center of mass. Their analysis found that cold and dense winter air shifts the balance toward Arabia, Asia, and northern Africa around Dec. 21 each year. Around June 21, the corresponding effect occurs over South America and South Africa.

GRACE Satellites Confirm the Mass Changes

The mass estimates produced by the new analysis agree with observations from the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission.

Launched in 2018, GRACE-FO consists of two satellites that measure monthly changes in Earth's gravitational field. Much of that changing gravity is caused by water moving above and below the planet's surface.

The satellites travel together in an extremely precise formation. When the leading spacecraft passes over a region containing extra mass, such as a river basin swollen with water, the stronger gravitational pull changes the distance between the two satellites by a tiny but detectable amount.

GRACE-FO is a partnership between NASA and the German Research Centre for Geosciences (GFZ).

Scientists are already preparing the next generation of these measurements. The GRACE-Continuity (GRACE-C) mission is targeting a launch in late 2028 and is intended to continue the nearly 25 year GRACE series record of tracking how water and mass move around Earth.

Story Source:

Materials provided by NASA. Original written by Sally Younger. Note: Content may be edited for style and length.

Journal Reference:

- Donald F Argus, Kevin M Gaastra, Bruce J Haines, Michael B Heflin, Felix W Landerer, Athina Peidou, David N Wiese, Geoff Blewitt, Corné Kreemer, Henryk Dobslaw, Matthew J Swarr. Estimation and cause of the seasonal oscillation between Earth’s centre of mass and centre of figure. Geophysical Journal International, November 2026 DOI: 10.1093/gji/ggag314

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