Planet 51: The Junior Novel — J.E. Bright

Everything seemed to be going just right for Lem, until the day an "alien" dropped out of the sky and landed in his backyard. With his entire planet in a tizzy over the alien invasion, Lem knows that it's up to him to help Chuck get back to his ship. Can Lem keep the astronaut--and himself--safe from the government agents on their trail? It's a race to the finish as Lem learns if he's got the right stuff to save the day.