The young Earth-Moon system formed after Earth was struck by a protoplanet, Theia, three times the size of Mars. Debris from the impact coalesced to form the Moon within a few thousand years. Initially, Earth and Moon were closer and spinning faster. Debris from the collision continued to rain down. Data from India’s Chandrayaan-3 mission supports the idea of a molten rock ocean once covering the Moon. Joshua Snape, a Royal Society University Research Fellow at the University of Manchester, contributed to this article, originally published in The Conversation and shared by Space.com.