Gravity Recovery and Climate Experiment (GRACE), U.S.-German Earth-mapping mission consisting of twin spacecraft GRACE 1 and 2 (nicknamedTom and Jerry after the cartoon characters). GRACE 1 and 2 were launched on March 17, 2002. By tracking the precise distance between the two spacecraft and their exactaltitude and path overEarth, scientists could measure subtle variations in Earth’sgravitational field and detect mass movements due to such natural activity assea level changes,glacial motions, and ice melting. GRACE observed an accelerating loss of ice in Greenland andAntarctica and the change in the gravitational field caused by the Sumatranearthquake responsible for the 2004Indian Ocean tsunami.