Tomorrow morning, NASA mission planners will begin steering two probes that are now circling the moon to a smashing demise. The craft—named Ebb and Flow in a NASA-sponsored contest won by schoolchildren in Montana—have been measuring subtle variations in the moon's gravitational field in unprecedented detail since soon after they entered lunar orbit a little less than a year ago. With the gravity-mapping mission now over, if all goes according to schedule, the probes' Thelma-and-Louise moment will occur at approximately 5:28 p.m. EST on Monday, 17 December, when the craft slam into a 2-kilometer-tall mountain in the northern polar regions of the moon, NASA announced in a press conference today. Both of the washing machine-sized craft trace the same path around the moon, but because one orbits about 44 kilometers ahead of the other one, the impacts will happen about 20 seconds apart. Although the probes will strike an area of the moon that's dark at the time and visible from Earth, it's not likely that backyard astronomers will be able to observe anything because the craft are small and their fuel tanks will be empty, researchers say. Before-and-after images of the region taken by the Lunar Reconnaissance Orbiter will provide data that will allow researchers to estimate the strength and cohesiveness of surface rocks at the impact sites.
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