Figure 11-10: Stripping Mercury’s Mantle by a Collision To account for Mercury’s high iron content, one theory proposes that a collision with a planet-sized object stripped Mercury of most of its rocky mantle. These four images show a supercomputer simulation of a head-on collision between proto-Mercury and a planetesimal one-sixth its mass.

(Courtesy of W. Benz, A. G. W. Cameron, and W. Slattery)