A pair of NASA moon-mapping probes smashed themselves into a lunar mountain on Monday, ending a year-long mission that is shedding light on how the solar system was formed.
The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft had been flying around the moon, enabling scientists to make detailed gravity maps. The probes sped up slightly as they encountered stronger gravity from denser regions and slowed down as they flew over less-dense areas.
By precisely measuring the distance between the two probes, scientists discovered that the moon’s crust is thinner than expected and that the impacts that battered its surface have done even more damage underground.
Out of fuel and edging closer to the lunar surface, the probes were commanded to smash themselves into a mountain near the moon’s north pole, avoiding a chance encounter with any Apollo or other relics left on the surface during previous expeditions.
“We do feel the angst about the end of the mission,” said Charles Elachi, director of NASA’s Jet Propulsion Laboratory in California, which oversaw the mission. “On the other hand, it is a celebration because this mission has accomplished tremendous science.”
The probes’ resting place was named after the first US woman in space, Sally Ride, who orchestrated GRAIL’s educational program before she died. Some of the probes’ cameras were operated by students.
After completing their primary mission in May, the GRAIL twins — each about the size of a small washing machine — moved closer to the lunar surface, dropping their orbits from about 55km to less than half that altitude to increase their sensitivity.
On Dec. 6, the probes, nicknamed Ebb and Flow, flew down to about 11km to make one last detailed map of the moon’s youngest crater.
“Ebb and Flow have removed a veil from the moon,” lead researcher Maria Zuber of the Massachusetts Institute of Technology said.