Temperatures on Mars range from -125 to 23 °F. The atmosphere is 95% carbon dioxide. Gravity is 2/5 of that which we experience on Earth. Despite the obvious extremes on the Red Planet, Mars is the most hospitable deep space environment accessible to humans for long duration missions. Scientists theorize that Mars cooled dramatically over time, but at one point could have supported liquid water and primitive life forms. Investigations on the fourth rock from the sun will help researchers better understand climate evolution, extraterrestrial biology, and planetary resources.