The only things I remember are a group of astronauts visit a Mars-like brown planet (or Mars itself) where they find a small group of humans living there. They are trapped because of some type of aliens which can appear in human shape.
Somehow a woman and a man finally save themselves and fly away, but the male is an alien who convinced everybody (at the beginning of the movie) that he is a human. Inside the spaceship, they have intercourse and the woman sleeps for some hours, or maybe years. When she wakes up she finds out the man is an alien and she is pregnant with an alien baby.
As far as I can remember the ship destructs before it lands on Earth. (I have other memories which the ship lands successfully, I don't know if this is from the same movie.)
Also the aliens were more like robots because their body had so much metal in it.
I watched it about 5 years ago but I believe the movie is older.