As planet Earth rang in the new year, a different kind of countdown was happening at the moon.

After a 3 1/2-month journey, a NASA spacecraft flew over the moon’s south pole, fired its engine and dropped into orbit Saturday in the first of two back-to-back arrivals over the New Year’s weekend.

Mission control at the NASA Jet Propulsion Laboratory erupted in cheers and applause after receiving confirmation that the probe was healthy and circling the moon. An engineer was seen on closed-circuit television blowing a noisemaker to herald the New Year’s Eve arrival. Despite the successful maneuver, the work was not over. Its twin still has to enter lunar orbit today