by Kasey Cunningham

Launched in an effort to discover more about the interior of the Moon, GRAIL was one of the most anticipated missions of the New Year, according to Discover News. The twin GRAIL spacecraft successfully entered into orbit around the Moon on December 31, 2011, and January 1, 2012, respectively.

The probes will map the gravitational field of the Moon, and these data will be used to then “X-ray” the planetary interior from the crust down to the core. The lunar surface is ancient and has been studied by American and Russian landers and well as numerous successful orbital missions. The lunar interior is less well known. Seismometers deployed from Apollo landers provided precious data about the lunar interior, and when combined with gravity data will illuminate both the structure and composition of the interior. Examining the Moon in its entirety will help solve mysteries surrounding the Moon’s origin, including the depth and crystallization of the lunar magma ocean, the size of the lunar core, and the deep structure of the lunar crust.

DTM Staff Scientist Sean Solomon is a co-investigator of the GRAIL mission science team. He states that GRAIL will produce valuable data that have not been possible to obtain before the dual-spacecraft mission.

“The Moon is the only solar system body other than Earth for which we have seismic data on interior structure, and thanks to the Lunar Reconnaissance Orbiter there is now an exquisitely detailed global map of the Moon's topography.  A major missing piece in the global geophysical exploration of the Moon has been a high-resolution gravity field, particularly for the lunar farside.  GRAIL will improve our knowledge of lunar gravity by two to three orders of magnitude, and with that new information a number of basic questions on the internal structure and evolution of Earth's only natural satellite will be addressable for the first time."

The GRAIL spacecraft are now in the “90 day science phase” where they will be collecting data that should reveal the Moon’s subsurface structures and ultimately, its thermal history.

The GRAIL mission science team reacts to the first spacecraft entering orbit.