Collision between two bodies of similar mass may explain the formation of Mercury

The formation of Mercury remains an unsolved mystery. The planet closest to the sun has a disproportionately large metallic core-accounting for about 70% of its mass-and a relatively small rocky mantle. Until now, the most widely accepted explanation was that Mercury lost much of its crust and mantle after colliding catastrophically with a large celestial body. However, dynamic simulations show that this type of impact involving bodies of very different masses is extremely rare.