The Gravity Recovery And Interior Laboratory, or GRAIL, will fly twin spacecraft in tandem around the Moon to precisely measure and map variations in the Moon's gravitational field. This detailed information will reveal differences in density of the Moon's crust and mantle and will help answer fundamental questions about the Moon's internal structure, thermal evolution, and history of collisions with asteroids.
The new knowledge about lunar gravity will significantly assist the planning of any future manned or unmanned missions to land on the Moon. The data can be used to help target desirable landing sites and to program the descent to the surface to avoid a crash landing.
Image Credit: NASA