It reminds me of the story of the Apollo 15 astronauts standing on the surface of the moon and dropping a feather and a hammer to demonstrate Galileo's theory of objects in gravity fields in vacuums. (nakedpastor.com)
The second is the gravity method, which utilizes NASA's GRACE satellite pair to essentially weigh the ice sheets from space (it measures minute changes in their flight path due to the shifting gravity field of mass below). (sciencemag.org)
To work out why the pole changed direction, Chen's team used data from NASA's GRACE satellite, which measures changes in Earth's gravity field over time. (newscientist.com)