The Mars mission in Andy Weir's “The Martian” is Ares 3.
In the novel, NASA's Ares 3 crew travels to Mars in the year 2035 for a planned month-long expedition. The astronauts land in Acidalia Planitia, but a powerful dust storm forces an emergency evacuation after only six sols. Botanist and mechanical engineer Mark Watney is struck by debris, presumed dead, and left behind when the rest of the crew escapes.
Watney survives and must extend the mission's supplies while finding a way to communicate with Earth. He grows potatoes inside the habitat, repairs equipment, and methodically solves engineering and logistics problems. The mission's name remains important because NASA's later rescue efforts must reconnect with the Ares program and its crew.
Ares 5 is a later mission in the story, not the expedition that strands Watney. Mars Direct is a real proposed mission architecture rather than the mission name in Weir's novel, and Ares 1 is not the correct expedition designation.