23 November 2012
Vol 338, Issue 6110

About The Cover

Cover image expansion

COVER The lower hemisphere of a fast-spinning Earth shown 2 hours after a giant impact. Colors denote the silicate mantles and iron cores of Earth and the impactor. The debris evolves into a Moon-forming disk composed primarily of material from Earth's mantle, explaining the isotopic similarity between Earth and the Moon. In this model, the fast-spinning Earth is slowed by an orbital resonance between the Moon and the Sun. See pages 1040, 1047, and 1052. Image: Sarah T. Stewart