Can anyone give me the name of this science fiction movie?

It was done probably in the nineties or early 2000s. In the movie, a Mars Viking lander returns to Earth carrying an alien "embryo." The embryo quickly grows up. They kill it (I think) but the alien leaves behind another embryo which develops. Anyway, the alien looks sort of like a centaur and it can retract it's head into it's body. At the end of the movie we find out that they weren't invading our world but came to ask us not to invade theirs.