Moon countdown: NASA probe enters lunar orbit

This undated artist rendering provided by NASA on Dec. 21,2011 shows the twin Grail spacecraft mapping the lunar gravity field. The two probes are scheduled to enter orbit around the moon over New Year's weekend. (AP Photo/NASA, Jet Propulsion Laboratory)

February 1, 2012 1:58:58 PM PST
A NASA spacecraft has successfully slipped into orbit around the moon.

A roomful of scientists and engineers monitoring the New Year's Eve maneuver clapped after the Grail-A probe signaled that it was circling the moon.

The celebration was brief. Mission team members looked ahead to New Year's Day when twin Grail-B was scheduled to perform the same move.

The duo will study the moon's gravity to determine what's inside straight down to the core.

The $496 million mission is managed by the NASA Jet Propulsion Laboratory.