![A NASA spacecraft has successfully slipped into orbit around the moon. The probe will, along with a twin probe, study the moon’s gravity to determine what’s inside straight down to the core.
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Image: This undated artist rendering provided by NASA on Dec. 21,2011 shows the twin Grail spacecraft mapping the lunar gravity field. (AP Photo/NASA, Jet Propulsion Laboratory)](http://24.media.tumblr.com/tumblr_lx3aheqoDL1qj5rqko1_500.jpg)
A NASA spacecraft has successfully slipped into orbit around the moon.
The probe will, along with a twin probe, study the moon’s gravity to determine what’s inside straight down to the core.
Image: This undated artist rendering provided by NASA on Dec. 21,2011 shows the twin Grail spacecraft mapping the lunar gravity field. (AP Photo/NASA, Jet Propulsion Laboratory)
