To describe The Last Days on Mars in one phrase would be a difficult task, but the closest thing I can think of after seeing this trailer is "An episode of The X-Files gone totally wrong." You know — if Mulder and Scully actually went to Mars and discovered some alien life form who was evil and hellbent on destroying humanity or something (which is kind of close to an X-Files episode anyway). Instead of Mulder and Scully, though, The Last Days on Mars has Liev Schreiber and Olivia Williams, and also some gooey alien who is in desperate need of a manicure.
The plot, as depicted in the trailer, follows a crew of astronauts at the tail-end of their first mission to Mars. One of them, Marko, thinks he's discovered fossils that evidence the existence (or previous existence) of bacterial life, but it turns out he's just discovered a gooey, man-eating ALIEN.
Since Marko doesn't know that yet, though (and because he's clearly never seen a horror movie), he disobeys orders and heads out to go gather more fossilized evidence, and ends up dead — then his fellow crew members end up stranded on Mars awaiting help while this alien who now has a taste for human blood is after them. Goddamnit, Marko! This is why we can't have nice things.
You can check out the trailer below. The Last Days on Mars is set to open in the U.K. on Sept. 19, and in the U.S. on Dec. 6.