Abstract

Mars has occupied a distinctive place in the popular imagination for a century. Science fiction and the wishful thinking of Percival Lowell primed us to think of Mars as a living world, but the first landers and orbiters witnessed a frigid and arid desert landscape. Now the pendulum has swung back toward habitability, with evidence of the red planet’s warmer and wetter history and hints of sub-surface aquifers. A Mars base with short-term occupants would be a first step toward eventual colonization. NASA is planning to send astronauts to Mars, subject to its limited and uncertain budget. Meanwhile, the private sector has ambitious plans for establishing a foothold on Mars, with the Mars One plans viewed more skeptically by experts than the plans of SpaceX. Mars colonists would face challenges caused by isolation, radiation, reduced gravity, and an unforgiving external environment. Over time, they would diverge culturally, psychologically, and genetically from the inhabitants of Earth.