The Falcon 9 booster was launched in 2015 but after completing its mission. It did not have enough fuel to return towards Earth and instead remained in space. Astronomer Jonathan McDowell told BBC News it will be the first known uncontrolled rocket collision with the moon. But the effects will be minor, he says. The rocket was abandoned in high orbit seven years ago. It was part of Musk's space exploration programme SpaceX, a commercial company that ultimately aims to get humans living on other planets.