Earth’s center of mass shifts about 3 millimeters toward the North Pole when snow peaks in March

Every March, when snow piled up across North America and Eurasia reaches its seasonal maximum, Earth’s center of mass moves about 3 millimeters toward the North Pole. The figure comes from a study led by Donald Argus, a geoscientist at NASA’s Jet Propulsion Laboratory in Southern California, which also finds that the planet’s back-and-forth wobble of mass is about half the size scientists believed eight years ago.

The center of mass is the reference point for measuring positions on Earth’s surface, in the atmosphere and in space, so a seasonal drift of a few millimeters matters to anyone who needs satellite navigation and elevation measurements to hold steady over years.

Snow in March, the Amazon in April

The snow figure is one piece of a larger seasonal pattern. According to NASA’s release of Sept. 16, 2026, snow accumulation in North America and Eurasia “reaches a maximum in March and shifts Earth’s center of mass about 3 millimeters toward the North Pole.” Rainwater in the Amazon River basin follows in April, peaking at 2,400 gigatons and swinging the center of mass 2.2 millimeters toward South America.

The 3 millimeters therefore describes what the snow does by itself, not the planet’s full annual excursion. NASA gives no single combined amplitude, saying only that the center of mass swivels by fractions of an inch and, at most, several millimeters, and it lists the contributions one at a time.

The study, “Estimation and cause of the seasonal oscillation between Earth’s centre of mass and centre of figure,” is slated for the November 2026 issue of Geophysical Journal International, as ScienceDaily’s Oct. 7 repost of the NASA release notes. The paper’s title names the comparison: the center of mass is where Earth’s mass balances, while the center of figure is the geometric middle of the solid planet, and the seasonal gap between them is what the team measured.

Water, ice and air: the rest of the annual cycle

Snow and the Amazon are the largest entries the release names, but it lists others. Southeast Asia’s monsoon peaks in November at about 600 gigatons, roughly six months after the Amazon’s peak. From August through October, meltwater and rainfall add mass to the oceans and pull the center toward the South Pacific. Changes in the Mediterranean, Red, North, Baltic and Barents seas contribute less.

The atmosphere has its own turn in the cycle, modeled in this study with a European Centre for Medium-Range Weather Forecasts dataset, with winter air pressing hardest where it is coldest and densest. Using a European Centre for Medium-Range Weather Forecasts model, the authors find that cold, dense winter air shifts the balance toward Arabia, Asia and northern Africa around December 21, and toward South America and South Africa around June 21.

Argus said the new estimate of the annual movement is about half of what he and colleagues believed eight years ago, which means less water and air mass travels between the hemispheres than earlier work implied. The release adds that two international estimates, from 2017 and 2023, differ from each other by 0.27 inches, or 7 millimeters, nearly as large as the signal being chased.

LAGEOS lasers and GRACE-FO gravity as the measuring sticks

The measurement leans on satellite laser ranging. Ground stations in more than 20 countries fire lasers at LAGEOS 1 and 2, passive satellites studded with reflective prisms, and time how long the light takes to return, which fixes the satellites’ orbits and, through them, the point around which they circle. NASA’s LAGEOS page gives launch dates of May 4, 1976, for the first and Oct. 22, 1992, for the second, a satellite the Italian Space Agency built from the original design, and notes that the satellites carry no sensors, electronics or moving parts.

Because the stations are unevenly spread across the globe, the team combined the laser data with GPS tracking and orbit data from several low Earth orbit satellites, and modeled how shifting loads of water and ice bend the crust and nudge the ground stations. As a cross-check, the mass estimates agree with GRACE-FO, which NASA lists as launched on May 22, 2018 to track the movement of Earth’s water.

Argus compared the problem to measuring the center of mass of a glob of Jell-O, a quote relayed by IFLScience, because the planet’s shape never stops changing. His JPL co-author Felix Landerer has said better reference systems could help mapping and navigation, including shipping logistics and precision agriculture.

The unresolved piece is precision. The 2017 and 2023 international estimates still differ by 7 millimeters, more than double the 3-millimeter snow signal in the new work, even as Argus says the annual movement is now estimated at about half the value believed eight years ago.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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