BBC: Astronomers are rethinking the nature of the impact that created Earth’s Moon. It had been thought that a relatively slow-moving planetary body struck Earth. Debris from both bodies would have been ejected into orbit around Earth and eventually coalesced into the Moon and a reconstituted Earth. As scientists compare the isotopic compositions of different elements taken from both Earth and the Moon, however, they are finding that the Moon is much more similar to Earth than previously believed. To better understand the nature of the collision, Andreas Reufer of the Center for Space and Habitability in Bern, Switzerland, and colleagues have been running computer simulations. They propose that Earth may have been struck by a larger and faster-moving body, which struck a more glancing blow and, as a result, lost a smaller amount of material. The group’s findings are to be published in the planetary science journal Icarus.