"The Earth and the moon are not twins born from the same planet, but they are sisters in the sense that they grew up in the same environment," said Hagai Perets, study co-author and astrophysicist at the Israel Institute of Technology in Haifa.
Researchers already knew the composition of the moon and Earth to be remarkably similar. Therein lay the problem. The chance of Earth having a primordial twin was considered slim to none. New analysis, detailed in the journal Nature, begs to differ, however.