Separated after birth
Scientists have long believed that the moon formed as a result of a collision between the early Earth and a smaller planet, but computer models of the giant impact have always predicted the wrong composition for the moon. Now, researchers at Harvard University and the SETI Institute are proposing a new spin on the giant-impact model to match the observed composition of the moon. The previous giant-impact models held that a small planet, Theia, hit the Earth, sending a cloud of debris from Theia into orbit that formed the moon. But the chemistry of the moon matches that of the Earth. Now, Sarah T. Stewart, a professor in Harvard’s Department of Earth and Planetary Sciences, and her SETI colleague Matija Ćuk propose a new model in which pieces of the Earth broke off and formed the moon. The researchers present a dynamic model of their theory, based on the results of chemical...