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A high resolution of the Moon’s gravity field produced using data from Ebb and Flow. Photo: NASA/JPL-Caltech/MIT/GSFC

For nearly a year, the twin satellites Ebb and Flow have been orbiting the Moon, measuring the subtle variations in lunar gravity as part of NASA’s GRAIL mission. But the satellites are out of fuel, and NASA has decided that it’s time for them to go away. On Monday, Ebb and Flow will burn the last of their fuel and set course for a mountain peak near the Moon’s north pole.

Though NASA will be watching the impact using other satellites, says Emily Lakdawalla, there won’t be much to be seen from here on Earth.

“The exercise will not be for the advance of science,” says Kenneth Chang for the New York Times, “but rather something of a garbage-disposal operation, to make sure that the probes — which are running out of fuel — do not come to rest in a historically significant place, like on Neil Armstrong’s footprints.”

In this way, the deaths of Ebb and Flow will differ from another recent NASA mission. In 2009, the LCROSS mission saw a 2.2 ton mass smash into the lunar surface at a speed of 1.5 miles per second, plowing into a crater, kicking up a plume of debris and helping scientists find evidence of water on the Moon.

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