Tracking the Center of the Earth

People might not be able to journey to the center of the Earth as Jules Verne envisioned in his classic science fiction novel, but scientists hope they might now pinpoint better where the center is, according to news from NASA's Jet Propulsion Laboratory (JPL) at the California Institute of Technology.

Knowing as precisely as possible where the Earth's center of mass is helps scientists generate more accurate data for changes in the world's sea levels, tectonic motion that leads to earthquakes and volcanic activity, and the slow rebounding of land masses still recovering from the heavy weight of glaciers during the last ice age.

Developed by JPL's Donald Argus, the new center-tracking technique combines data from four sources: a network of global positioning system receivers, a network of satellite-tracking laser stations, a French network of satellite-tracking instruments and a network of radio telescopes that are used to measure the Earth's position in relation to quasars at the edge of the known universe. Argus says the new strategy enables scientists to locate our home planet's center of mass to within 1 millimeter (about 0.04 inches) a year. Previously used techniques have been accurate only to about 2 to 5 millimeters (or about 0.08 to 0.2 inches) per year.

"By its very nature, Earth's reference frame is moderately uncertain no matter how it is defined," Argus said. "The problem is very much akin to measuring the center of mass of a glob of Jell-O, because Earth is constantly changing shape due to tectonic and climatic forces. This new reference frame takes us a step closer to pinpointing Earth's exact center."

Knowing as closely as possible where the Earth's center is can help scientists better measure, for example, how quickly the ice sheets in Greenland and Antarctica are melting into the ocean, Argus said. Currently, uncertainties in pinpointing the Earth's center lead to uncertainties in how quickly global sea levels are rising.