Twin NASA probes began studying the moon's gravity late Tuesday night in effort to determine why the moon, Earth's only natural satellite, is shaped the way it is.
Managed locally at NASA's Pasadena-based Jet Propulsion Laboratory, the three-month GRAIL mission (Gravity Recovery And Interior Laboratory), will begin analyzing data in one month.
Scientists want to know why the Pink Floyd side of the moon appears to be more mountainous than the side that always faces Earth. Despite numerous missions, they still don't have that answer.
Additionally, by mapping the lunar gravity field, investigators hope to support or discredit a theory that Earth at one time had two moons.
Researchers hope the $496 million mission -- which includes spacecraft development, science instruments, launch services, mission operations, science processing and relay support -- will net significant intel about what lies below the surface.
The probes entered orbit around the moon on New Year's weekend, but needed to assume their position, 35 miles above the surface, before starting data collection.
Check out the official mission kit for fun moon facts like, "If Earth did not have its moon, Earth would spin three times as fast, making a day last only 8 hours instead of 24," and a detailed look at the GRAIL mission’s six science investigations.