By taking more than 70 million observations during its first 2 years in orbit, a limousine-length satellite has given scientists their most detailed map yet of Earth's gravitational field. The lumpiness of that geoid—the theoretical surface that a planet-wide ocean would take if there were no tides or currents—betrays the irregularity of the planet's mass distribution, including concentrations of mass such as mountain ranges and ice sheets. Yellows and reds mark areas of higher-than-normal gravitational strength; blue shades are lower than normal. The unprecedented precision of the new geoid, released today  by the European Space Agency at a workshop for scientists in Munich, will lead to better understanding of the speeds and paths of ocean currents, as well as improved estimates of how they disperse pollutants, the researchers say. The geoid will also provide new insights about geological processes occurring deep within Earth, such as the movement of one tectonic plate being shoved beneath another, and when combined with other data will help improve estimates of the thickness and mass of polar ice sheets.
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