GRAIL mission delivers a hi-fi map of the moon

A pair of NASA orbiters has given scientists their highest-fidelity look at the moon, a leap that could help explain the evolution of the solar system's rocky planets, including Earth.

Scientists announced the first results Wednesday from the $496-million GRAIL mission, the Gravity Recovery and Interior Laboratory, which consists of two washing-machine-size spacecraft that operate in tandem. GRAIL lifted off from Cape Canaveral, Fla., in September 2011, and the spacecraft are now circling the moon, studying its structure, surface and composition.

GRAIL's new gravity-field map is a detailed study of the moon — a view of its volcanic landforms, peaks and craters in unprecedented fidelity. Scientists said GRAIL had mapped minute hiccups in the lunar gravity field, which provides a preserved record, effectively, of the battering from space that the moon endured after its formation.

GRAIL found that fractures in the moon's interior extend to its deep crust and potentially beyond, and that below the surface, its crust is virtually pulverized. The spacecraft also determined that the average thickness of the lunar crust is between 21 and 27 miles — as much as 12 miles thinner than previously thought.

Considering that a dozen humans have walked on the moon, significant gaps remain in science's understanding of Earth's nearest neighbor.

Knowing the precise composition of the moon is considered crucial to unlocking secrets of the formation of the solar system, because the moon's interior has remained relatively undisturbed — certainly compared with Earth — for billions of years. Inside are remnants of the earliest days of the solar system. GRAIL is using gravity as a lens to make those calculations.

"What this map tells us is that more than any other celestial body we know of, the moon wears its gravity field on its sleeve," said the mission's principal investigator, Maria Zuber, a professor of geophysics at the Massachusetts Institute of Technology.

The Jet Propulsion Laboratory in La Canada Flintridge is managing the mission.