Any way, The Martian is about an astronaut, Mark Watney, who gets stranded on Mars when his expedition leaves due to an emergency. The novel then becomes a struggle by Watney to survive until he can be rescued. It's a damned fine novel and an example of the hardest type of science fiction.
AICN reports the first round of viral marketing for the film has hit:
I was excited to see Jessica Chastain in the case, and wikipedia indicates there's also some Chiwetel Ejiofor and Sean Bean action.