Figure 6-43The Stripping of Mercury’s Mantle To account for Mercury’s high iron content, one theory proposes that a collision with a massive planetesimal stripped Mercury of most of its rocky mantle. These three images show a computer simulation of a nearly head-on collision between proto-Mercury and a body one-sixth its mass. Both worlds are shattered by the impact, which vaporizes much of their rocky mantles. Mercury eventually reforms from the remaining iron-rich debris. The rest of the original Mercury and the impactor leave this area of the solar system.