Mark Watney vs. A Planet

In The Martian, the protagonist is Mark Watney. He is an astronaut, the last-in-command of the third mission to Mars. He is stranded when an evacuation is called prior to a massive storm that separates him from his group and maroons him alone on the red planet. He is resourceful, strong, resilient, stubborn, and above all a massive smart-aleck. Physically, he is lean and without much fat while also managing to be one of the smallest astronauts on the mission. I believe that the antagonist of the book is Mars itself. While it does not consciously do so, it throws challenges at Watney that he must overcome and generally builds itself to be a good antagonist.