It’s similar to pursuing a moving goalpost, although it is essential for maintaining the accuracy of satellite navigation and global measurements.
This hybrid approach reduces uncertainty and offers a sharper picture of how Earth’s center of mass moves seasonally, a key advance for navigation, climate studies, and geophysics.
Argus said, “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.
To make this clearer, the study provided vivid examples:In March, snow accumulates over both North America and Eurasia, causing the Earth’s center to shift by about 3 mm towards the North Pole.
These mass movements were cross‑checked with NASA’s GRACE‑FO mission, whose twin satellites measure tiny changes in Earth’s gravity as water shifts above and below ground.
Geophysicists usually regard the center of a geodetic network (CN) as a stand-in for the Earth’s center of figure (CF) and consider the displacement of the CN with respect to the center of mass (CM) to be a record of atmospheric, oceanic, and water movements between the hemispheres.
In reality, however, the CN is a poor substitute for the CF since the Earth’s fluid envelope, namely the atmosphere, the oceans, and water, elastically deforms the solid Earth and thus causes the CF to shift in ways that are not picked up by the CN.
The situation is made worse since half of the satellite laser ranging (SLR) stations are located in Europe and North America, causing the CN value to differ from a genuine global average. Although SLR is able to accurately determine CM (the point about which the satellites orbit), the uneven spread of the ground stations causes CN to diverge from CF and thus reduces the accuracy of tracking changes in Earth.
Imagine the centre of mass of Earth as a kind of invisible benchmark which satellites employ when navigating and determining heights; yet since our planet is not a solid marble, it undergoes continual movement due to the presence of the oceans, the ice causing it to sag, and the air causing it to swell, and as a result the benchmark shifts by a few millimeters each season.
NASA’s Jet Propulsion Laboratory has now worked out a method for tracking those slight seasonal variations with great accuracy, producing clear pictures of the spring thaws, the dense air of winter, and the restless oceans pushing Earth’s center back and forth. It’s similar to pursuing a moving goalpost, although it is essential for maintaining the accuracy of satellite navigation and global measurements.
The existing methods for measuring the Earth’s center-of-mass ‘swivel’ are surprisingly inaccurate. The two most recent global estimates, those from 2017 and 2023, differed by about 7 millimeters, a distance equivalent to the height of three stacked nickels.
This discrepancy is almost as great as the movement itself. In order to improve accuracy, scientists at JPL, including Donald Argus, devised a new method that combines GPS tracking with orbital data obtained from a number of low-Earth-orbit satellites, incorporating a wider variety of targets than the conventional laser-ranged LAGEOS satellites. Importantly, the technique also takes into account the way in which the weight of water and ice distorts Earth’s crust and causes the ground stations to move with those distortions.
This hybrid approach reduces uncertainty and offers a sharper picture of how Earth’s center of mass moves seasonally, a key advance for navigation, climate studies, and geophysics.
Argus said, “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. Our findings suggest that the mass of Earth’s water and air moving between the hemispheres is smaller than previously thought.”
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.”
The center of mass of the Earth does not remain fixed but oscillates seasonally as the oceans, the atmosphere, and the water on the continents move around the globe. To make this clearer, the study provided vivid examples:
In March, snow accumulates over both North America and Eurasia, causing the Earth’s center to shift by about 3 mm towards the North Pole. In April, the Amazon River basin accumulates about 2,400 gigatons of rainwater, and this causes the center to shift by 2.2 mm towards South America.
In November, the monsoon in Southeast Asia reaches its peak with about 600 gigatons of water, contributing to the annual wobble. Keep your voice across everything you write with real-time suggestions.
The atmosphere also plays a role: dense winter air tips the balance over Arabia, Asia, and northern Africa around December 21, and over South America and South Africa around June 21.
These mass movements were cross‑checked with NASA’s GRACE‑FO mission, whose twin satellites measure tiny changes in Earth’s gravity as water shifts above and below ground. Together, the findings show how snow, rain, monsoons, and ocean swells subtly tug Earth’s balance point back and forth, a planetary heartbeat measured in millimeters.
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