The mission to Mars is looking for any signs of life. They find it all right, in the form of a deadly bacterium that not only kills the humans it infects, but does it quickly - in well less than an hour - and turns them into vicious zombies without pulse or need for oxygen, but a drive to attack and therein infect other humans - i.e., the rest of the mission.
There's a cold and logical ecological aspect to this. Since Mars is devoid of oxygen, it makes sense that the bacteria would turn the human invaders aka astronauts into creatures that need no oxygen. Perhaps this is what the original denizens of Mars were like, though we see no real suggestion of this in the movie.
The ending is nicely - i.e., harrowingly - ambiguous. Does the astronaut survivor, who may be infected, allow himself to be rescued, and therein risk bringing the contagion back to Earth, or commit a noble suicide?
Given what we've seen in The Walking Dead, we might have our answer. But The Walking Dead is of course another reality, which may or may not be linked to The Last Days on Mars - obviously the movie and the comic book/television series are not, so I'm talking metaphysical popular culture. But we've yet to see - at least in the television series - any indication of what caused the plague on Earth, so I'll opt to look at The Last Days on Mars as a strong, scientific prequel. And, hey, nice to Liev Schreiber (Ray Donovan) and Romola Garai (The Hour) on a screen together.
See also The Walking Dead 4.1: The New Plague ... The Walking Dead 4.2: The Baby and the Flu ... The Walking Dead 4.3: Death in Every Corner ... The Walking Dead 4.5: Hershel, Carl, and Maggie
And see also The Walking Dead Back on AMC ... The Walking Dead 2.2: The Nature of Vet ... The Walking Dead 2.3: Shane and Otis ... The Walking Dead 2.4: What Happened at the Pharmacy ... The Walking Dead 2.6: Secrets Told ... The Walking Dead 2.7: Rick's Way vs. Shane's Way ... The Walking Dead 2.8: The Farm, the Road, and the Town ... The Walking Dead 2.9: Worse than Walkers ... The Walking Dead 2.11: Young Calling the Shots ... The Walking Dead 2.12: Walkers Without Bites ... The Walking Dead Season 2 Finale