For nearly a year, a pair of small identical science satellites have been circling the moon, enabling scientists to piece together detailed gravity maps showing what is beneath the battered lunar surface.
That mission came to an end on Monday when the probes, nicknamed Ebb and Flow, flew themselves into a mountain near the moon's northern pole, a dramatic, but planned finale to a successful year-long mission.
"We do feel the angst about the end of the mission. On the other hand, it is a celebration because this mission has accomplished tremendous science," said Charles Elachi, director of NASA's Jet Propulsion Laboratory in Pasadena, Calif., which managed the Gravity Recovery and Interior Laboratory, or GRAIL, program.
Ebb and Flow's end came 20 seconds apart at 5:28 p.m. EST, when radio links with the probes went dead.
The crash site was named after astronaut Sally Ride, the first American woman in space, who orchestrated GRAIL's educational outreach program before she died in July.
The probes included cameras that were operated by students.
Scientists are still crunching through data collected by GRAIL during its extended mission and a final, 7-mile-high pass over the moon's youngest crater. Already, the gravity maps produced during the first part of the mission have painted a picture of a young moon whose scarred surface hides an even more battered interior. The maps also showed the moon's crust is thinner than expected and that it is shot through with lava-filled cracks, evidence that the early moon expanded shortly after its formation.