WANDER among the asteroids and you’ll see anything from tumbling, pitted mountains hundreds of kilometres across to groups of fast-spinning fragments. Now a new simulation suggests why: the larger ones are primordial “planetesimals”, the original building blocks of the solar system, while their tiny cousins are chips flung out by collisions.
Bill Bottke at the Southwest Research Institute in Boulder, Colorado, and colleagues created a model of the history of collisions in the early solar system and compared it to the size, spin rate and orbits of many of the known asteroids. They also took into account the surface brightness…
