Planet 51 is a planet populated by little green aliens that live a world similar to ours from the 1950's. The animated film focuses around Lem (Justin Long), a teenage alien and his friend, Skiff (Sean William Scott). Lem works at the local planetarium while Skiff, who's a geek, enjoys working at a local comic book store. In a hidden base on the planet are stored artifacts from Earth. Out of these is a wheeled probe called the Rover who breaks out one night and starts sending signals in search of astronauts. Meanwhile a human spaceship lands in the backyard of Lem's house where they're having a barbecue with the family and friends. Lem tries to introduce Chuck to the reporters but it only creates chaos.