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NASA’s September 16, 2026 report describes a small seasonal shift in Earth’s center of mass, not movement of the planet’s solid core. As water, ice, and air move around the globe, they redistribute mass and shift the geocenter by millimeters relative to Earth’s geometric center. NASA’s updated satellite-tracking method estimates the yearly back-and-forth motion at about half the size researchers believed eight years earlier.
What NASA means by “Earth’s center” moving
Earth has more than one useful “center.” The geometric center is the center of the planet’s overall shape. The center of mass, also called the geocenter, is the balance point of all the planet’s mass. When water, ice, and air shift from one region to another, they change where that balance point lies by several millimeters.
This is a change in the location of a reference point, not a claim that Earth’s solid core is moving or that the planet has changed its orbit. NASA is describing seasonal mass redistribution across Earth’s surface and atmosphere.
How satellites reveal the shift
Satellites respond to Earth’s gravity and orbit around its center of mass. Researchers can infer geocenter changes from small variations in distances between satellites and ground stations. NASA’s reported method combines GPS tracking and orbital information from several low Earth orbit satellites with satellite laser ranging. It also models how water and ice loads deform Earth’s crust, because that deformation moves the ground stations used in the measurements.
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That combination addresses a limitation of earlier satellite laser ranging, which relied on a globally uneven distribution of stations. The approach was developed by Donald Argus with colleagues at NASA’s Jet Propulsion Laboratory, the University of Nevada, the University of Montana, and Germany’s Helmholtz Centre for Geosciences. NASA says the calculations agree with observations from the GRACE-FO mission, whose twin satellites map monthly changes in Earth’s gravity, primarily associated with water moving above and below ground. GRACE-FO is a partnership with Germany’s GFZ.
NASA’s account also points to the precision needed for satellite laser ranging: it measures the distance to satellites using laser pulses and helps establish reference systems for geodesy. NASA Goddard’s overview of satellite laser ranging describes the technique and its role in observing Earth.
Why the estimate is smaller than earlier estimates
The change is partly a measurement story. NASA says international geocenter estimates from 2017 and 2023 differed by 7 millimeters (0.27 inches)—nearly as large as the seasonal motion being estimated. The newer approach seeks to reduce uncertainty by combining more satellite-tracking information and accounting for crustal deformation that carries observing stations along with the ground.
JPL geoscientist Donald Argus said the new estimate of the annual back-and-forth movement is about half what researchers believed eight years earlier. NASA’s report does not give a single headline amplitude for that annual movement, so the “half” comparison should not be mistaken for a precise new millimeter total.
What shifts Earth’s center through the year
The seasonal swing reflects changes in three broad reservoirs: continental water, oceans, and the atmosphere. Continental water includes snow and ice as well as lakes, rivers, soil moisture, and groundwater. NASA highlights these seasonal examples:
- March: Snow accumulation in North America and Eurasia reaches a maximum, shifting the geocenter about 3 millimeters toward the North Pole.
- April: Rainwater in the Amazon River basin peaks at 2,400 gigatons and shifts the geocenter 2.2 millimeters toward South America.
- August through October: Ocean mass increases with meltwater and rain, shifting the geocenter toward the South Pacific. NASA says this large Pacific change outweighs changes in other oceans during this part of the seasonal pattern.
- November: Southeast Asian monsoon water reaches a maximum of 600 gigatons and contributes slightly to the annual oscillation.
- Around June 21 and December 21: Seasonal patterns in cold, dense air also affect mass balance. NASA describes effects over South America and South Africa around June 21, and over Arabia, Asia, and northern Africa around December 21.
These are examples of contributions to a global balance, not separate movements of the planet. NASA’s visualization depicts geocenter motion from 1993 to 2017; that interval is not identified as the observation period for the newer method.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why a millimeter-scale shift matters
A few millimeters is tiny in everyday terms, but geocenter location matters when building precise reference systems. NASA says those systems support satellite navigation and elevation measurements. Small errors in the reference frame can matter for applications that depend on accurate positions, including mapping and navigation.
As JPL study coauthor Felix Landerer put it, understanding the processes that change reference systems can help improve them for uses ranging from global shipping logistics to precision agriculture. The practical value of the finding is therefore not that people will notice Earth’s center moving, but that scientists can better account for a subtle change when measuring locations on and around the planet.
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