This Island Earth (1955)

Dr. Meacham is chosen along with others by the inhabitants of the planet Metaluna to do research that will help save their dying planet. However, an evil scheme is uncovered by the suspecting Dr. Meacham when he discovers the Metalunan's plan to take over Earth. Dr. Meacham then escapes an exploding Metalunan built Earth lab along with Dr. Adams only to be kidnapped while flying away in a small plane. A flying saucer wisks both the scientists off to Metaluna where they are held accountable for blowing up the Metalunan Earth lab during their escape. They later escape there with the help of Exeter the friendly Metalunan. Metaluna then self destructs and the Doctors make it safely back to Earth, which is saved from Metalunan invasion.