A mission to map the moon's hidden interior comes to a crashing end.
On December 17, 2012, two NASA spacecraft slammed into a ridge near the moon's north pole. The collisions marked the planned end to NASA's GRAIL (Gravity Recovery and Interior Laboratory) mission. Flying in formation, the twin, washing machine-sized probes, named Ebb and Flow, spent 351 days in lunar orbit mapping the moon's gravitational field. The maps revealed features of the lunar surface and interior in incredible detail, providing scientists with new information about the moon's craggy topography and lumpy crust. Using these maps, researchers will be able to peer back at the moon's early history and better understand its origin and development, along with that of Earth and the other rocky bodies in the solar system. The visualization shows the two spacecraft's final three orbits and their mission-ending crash.