Artist’s concept of the twin GRACE satellites. Image Credit: NASA
The twin satellites of the Gravity Recovery and Climate Experiment (GRACE) mission have been collecting data about how water moves and is stored around Earth for 15 years – three times longer than originally planned. GRACE, a joint effort between NASA and two German agencies, was launched on March 17, 2002.
“With GRACE, we effectively created a new field of spaceborne remote sensing: tracking the movement of water via its mass,” said Michael Watkins, the original GRACE project scientist and now director of NASA’s Jet Propulsion Laboratory, Pasadena, California.
The greater an object’s mass is, the greater its gravitational pull. Massive mountain ranges exert more gravitational pull than flat plains. While this small difference isn’t noticeable to humans, it can be detected by satellites. When they orbit the Earth, satellites speed up slightly as they approach a massive object and slow down as they move away from it. Measuring changes in mass has been crucial to discovering how water and the solid Earth are changing in places that can’t be seen directly.
“The completely new idea about GRACE was the perception that measuring and tracking mass gives you a ...