Earth's centre of mass is MOVING, NASA warns - and it could wreak havoc on satellite positioning data and navigation systems

Earth's centre of mass is constantly moving in time with the seasons, experts have revealed. A team of scientists at NASA said our planet is continually sloshing and sagging under the weight of water, ice and air.These are all affected by winter freezes, springtime thaws, churning oceans and changing atmospheric pressure.Because of this, Earth's centre of mass swivels around its geometric centre by as much as several millimetres, they revealed.And it could be throwing off satellite data and navigation systems.'While these movements might appear tiny, our modern world relies on extremely accurate positioning measurements,' co-author Felix Landerer, from NASA's Jet Propulsion Laboratory, said.'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.' Earth's centre of mass is constantly moving thanks to springtime thaws, churning oceans and dense winter air, NASA revealed Earth's centre of mass continually swivels around its geometric centre by as much as several millimetres as the seasons changeDriven by gravity, satellites naturally orbit Earth's centre of mass as if bound by invisible tethers.Therefore, tiny changes in the distance between satellites and ground stations reflect Earth's shifting centre of mass.Dense metal satellites resembling enormous disco balls are already orbiting Earth, and have done so for decades.But they are limited by the uneven distribution of ground stations around Earth – which can make measurements slightly less accurate.For the study, published in Geophysical Journal International, lead author Donald Argus and his team developed a new technique to track the size of Earth's swivel based on ultraprecise satellite tracking.They added GPS tracking, as well as orbital data from several other satellites in low Earth orbit to provide a diverse array of 'targets'.It also considers how the weight of water and ice can deform the Earth's crust – and how this can affect ground stations, too.The scientists tracked Earth's centre of mass oscillating with the seasons, and said this is likely caused by changes to the oceans, atmosphere and continental water as the months go by. A team of scientists at NASA said our planet is continually sloshing and sagging under the weight of water, ice and air The scientists tracked Earth's centre of mass oscillating with the seasons, and said this is likely caused by changes to the oceans, atmosphere and continental water as the months go byThey found that snow accumulation in North America and Eurasia reaches a maximum in March and shifts Earth's centre of mass about three millimetres toward the North Pole.A month later, in April, rainwater in the Amazon River basin peaks at 2,400 gigatons, swinging Earth's centre of mass 2.2 millimetres toward South America.Monsoon water in southeast Asia attains a maximum of 600 gigatons seven months later in November, adding slightly to the annual oscillation.Between August and October, the oceans swell with meltwater and rain, and Earth's centre of mass shifts toward the South Pacific Ocean.They also found that cold, dense, winter air helps tip the scales over Arabia, Asia, and northern Africa around December 21 each year, and over South America and South Africa around June 21.Overall, they discovered that the Earth's centre of mass is actually moving 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,' Dr Argus said. 'Our findings suggest that the mass of Earth's water and air moving between the hemispheres is smaller than previously thought.'Alongside Earth's centre of mass, scientists have confirmed the geographical North Pole is also moving – and could shift nearly 90 feet (27 metres) by 2100.As the planet's ice sheets and glaciers melt, this is causing a rapid redistribution of the Earth's mass, causing the pole to shift.Researchers measured the movement of the poles between 1908 and 2000 and compared this with projections of ice melt to see how far they might move in the future.In the worst-case scenario, in which greenhouse gas emissions are not reduced, the dramatic melting of the ice sheets will have moved the poles 89 feet between 1900 and 2100.In a more optimistic scenario in which greenhouse gas emissions are reduced, the North Pole will still move as much as 39 feet (12 metres).EARTH'S LIQUID IRON CORE CREATES THE MAGNETIC FIELD Our planet's magnetic field is believed to be generated deep down in the Earth's core.Nobody has ever journeyed to the centre of the Earth, but by studying shockwaves from earthquakes, physicists have been able to work out its likely structure.At the heart of the Earth is a solid inner core, two thirds of the size of the moon, made mainly of iron. At 5,700°C, this iron is as hot as the Sun's surface, but the crushing pressure caused by gravity prevents it from becoming liquid.Surrounding this is the outer core there is a 1,242 mile (2,000 km) thick layer of iron, nickel, and small quantities of other metals. The metal here is fluid, because of the lower pressure than the inner core.Differences in temperature, pressure and composition in the outer core cause convection currents in the molten metal as cool, dense matter sinks and warm matter rises.The 'Coriolis' force, caused by the Earth's spin, also causes swirling whirlpools.This flow of liquid iron generates electric currents, which in turn create magnetic fields.Charged metals passing through these fields go on to create electric currents of their own, and so the cycle continues.This self-sustaining loop is known as the geodynamo.The spiralling caused by the Coriolis force means the separate magnetic fields are roughly aligned in the same direction, their combined effect adding up to produce one vast magnetic field engulfing the planet.