Earth's Center of Mass is Shifting Seasonally, NASA Warns

Earth's center of mass is in constant motion, subtly shifting with the changing seasons due to the redistribution of water, ice, and air, according to NASA scientists. These movements, occurring in time with seasonal cycles like winter freezes, spring thaws, and ocean currents, cause the planet's center of mass to swivel around its geometric center by several millimeters annually.

This phenomenon could have implications for the accuracy of satellite positioning data and navigation systems, which rely on precise measurements. "While these movements might appear tiny, our modern world relies on extremely accurate positioning measurements," said co-author Felix Landerer of NASA's Jet Propulsion Laboratory. "By unravelling 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."

Satellites naturally orbit Earth's center of mass. Tiny changes in the distance between satellites and ground stations can therefore reflect shifts in this center. For decades, dense metal satellites have orbited Earth, but their measurements can be limited by the uneven distribution of ground stations.

To better track these subtle movements, researchers developed a new technique using ultra-precise satellite tracking data, including GPS and orbital data from multiple low Earth orbit satellites. The study, published in Geophysical Journal International, also accounts for how the weight of water and ice can deform the Earth's crust, affecting ground stations.

The scientists observed Earth's center of mass oscillating with the seasons, attributing these shifts to changes in oceans, atmosphere, and continental water.

Specifically, snow accumulation in North America and Eurasia causes the center of mass to shift about three millimeters toward the North Pole by March. In April, peak rainwater in the Amazon River basin shifts the center of mass 2.2 millimeters toward South America. Monsoon rains in Southeast Asia contribute to the annual oscillation between August and October, while oceans swelling with meltwater and rain also influence the center of mass, shifting it toward the South Pacific Ocean. Additionally, dense winter air over regions like Arabia, Asia, northern Africa, South America, and South Africa contributes to these seasonal shifts.

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

This research also comes as scientists have confirmed the geographical North Pole is also moving, with projections indicating a potential shift of nearly 90 feet by 2100. This polar movement is largely attributed to the redistribution of Earth's mass caused by melting ice sheets and glaciers, a phenomenon linked to climate change. Researchers project that under a worst-case scenario of unmitigated greenhouse gas emissions, the poles could shift 89 feet between 1900 and 2100. A more optimistic scenario, with reduced emissions, still anticipates a pole shift of up to 39 feet.