NASA STUDY TRACKS SEASONAL SHIFT IN EARTH'S CENTRE OF MASS

Scientists at NASA's Jet Propulsion Laboratory in Southern California have developed a new technique to measure how Earth's centre of mass shifts with the seasons, according to the space agency. The team, led by JPL geoscientist Donald Argus, published its findings in a study in Geophysical Journal International. NASA said the method relies on ultraprecise satellite tracking to calculate the seasonal swings with greater accuracy than previous approaches. The centre of mass, also known as the geocenter, is a key reference point used in satellite navigation and elevation measurements, the agency said. Earlier space-based techniques have attempted to pin down its position over past decades, NASA noted.

According to NASA, the redistribution of water, ice and air across the planet each year causes its centre of mass to move relative to its fixed geometric centre. The agency said this happens because Earth is not a solid, uniform sphere but instead sags and shifts under seasonal changes such as springtime thaws, ocean currents and dense winter air masses. NASA said the geocenter swivels around the geometric centre by as much as several millimetres, or fractions of an inch, over the course of a year. The agency's Space Geodesy Project uses a combination of space- and land-based methods to track this movement, including an animation covering the period from 1993 to 2017.

NASA said the two most recent international estimates of the scale of this swivel, produced in 2017 and 2023, differed from each other by 0.27 inches, or seven millimetres, roughly the height of three stacked nickels. The agency said this gap is almost as large as the seasonal motion the estimates are meant to measure, underlining the level of uncertainty in existing methods. Argus's team developed the new satellite-tracking technique specifically to reduce that uncertainty, according to NASA. The agency said accurate tracking of the geocenter remains important for the precision of satellite positioning and elevation data.