The geodetic effect is caused by a distortion that the Earth's mass makes in the fabric of space.

ECONOMIST: A new satellite will test Einstein's magnum opus

This phenomenon is a spiral distortion of space which should if relativity is correct happen when massive bodies rotate. (In essence, such bodies drag space round with them.) Frame-dragging is predicted to cause an additional precession of one hundred-thousandth of a degree, perpendicular to that caused by the geodetic effect.

ECONOMIST: A new satellite will test Einstein's magnum opus

Based on the Phoenix lander, the craft is tasked with giving us a peek beneath the planet's surface, armed with tools that include a geodetic instrument from the Jet Propulsion Laboratory, which will be used to calculate Mars' rotation axis, a seismic wave sensor and a subsurface heat probe, to measure the planet's internal temperature.

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