How the Earth came by its Moon has always been something of a mystery: Scientists had theorised that a Mars-sized planet, called Theia, crashed into Earth and that the moon formed from the debris. But, analysis of the rock chemistry from the lunar surface reveals that the moon and Earth are practically identical. There appeared to be no chemical trace of Theia. So where did it disappear to? This chemical conundrum has thrown a lot of doubt on the impact theory. But a series of papers in the journal Nature suggests that the theory still holds up. Using simulations and isotope measurements,... Like this podcast? Please help us by supporting the Naked Scientists