When a space colony team land on a habitable planet, they discover a buried alien race and an object that threatens the fate of their lives – and the earth.

Solid. Some grammar suggestions. Land should be a singular verb. Buried alien race is a little awkward if you're trying to convey that the race is extinct. Fate of their lives is really redundant. How about "When space colonists land on a habitable planet, they discover the remains of an alien race and an object that threatens both their lives and the existence of earth."

Sounds to me a bit familiar - Like Aliens or Prometheus. How can you make it more unique?

Cool. Sounds like a film that I would like to see. The only critique I could think of is to possibly mention something about the protagonist(s).