The moon formed when a Mars-sized body called Theia hit it early on . But no one is sure why the moon and Earth have a similar composition . Israel Institute of Technology researchers say cloud of debris rained on worlds . But University of Maryland says impactor was similar to Earth .
The moon formed when a Mars-sized body called Theia hit it early on . But no one is sure why the moon and Earth have a similar composition . University of Maryland researchers say cloud of debris rained on worlds . But Israel Institute of Technology says impactor was similar to Earth .