An artist's depiction shows the twin spacecraft that comprise NASA's Gravity Recovery And Interior Laboratory mission

 
An artist
An artist's depiction shows the twin spacecraft (Ebb and Flow) that comprise NASA's Gravity Recovery And Interior Laboratory (GRAIL) mission. A pair of NASA moon-mapping probes smashed themselves into a lunar mountain on December 17, 2012, ending a year-long mission that is shedding light on how the solar system formed. REUTERS/NASA/JPL-Caltech/MIT/Handout