Hit and Run Planets - Universe Today
The composition of many planets, asteroids and meteorites could be explained by the theory of "hit-and-run" collisions. Scientists originally believed that the four terrestrial planets (Mercury, Venus, Earth and Mars) were formed slowly over time as material built up by accretion. But it's entirely possible that objects sideswiped each other, and continued on; although, with both parties pretty banged up. Large objects don't even have to touch to do massive damage to each other through their gravitational influence.