The two probes that make up NASA's GRAIL mission, which precisely measured the gravitational field of the Moon to create a gravity map, will crash
into the Moon tomorrow Dec 17 at about 2:28 p.m. PST (5:28 p.m. EST, 10:28 p.m. UTC). The probes will impact a mountain side near the lunar north
pole. Both spacecraft will hit the surface at 3,760 mph (1.7 kilometers per second). No imagery of the impact is expected because the region will be
in shadow at the time.
As a final test, the probes will burn off the remaining fuel, to help scientists gauge how much fuel the probes used up during the mission and how
much was left. This helps them plan future mission, because fuel meters don't work in zero-g and scientists have to guess in advance how much fuel is
needed for a particular mission.
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