The Battle For Earth

After S. E. T. I. receives an SOS from a planet eleven light-years from Earth, a group of nine astronauts from around the world volunteer to go on a rescue mission. Once they arrive at planet X, they discover that the entire planet has been decimated. When they return to Earth eleven years later, they learn that Earth has been conquered by flesh-eating aliens, the same ones that decimated planet X.
The astronauts ban together to save humanity from complete annihilation and wind up being the last line of defense against the flesh-eating aliens as the battle for Earth begins.