The colonization of Mars by humans is the focus of speculation and serious study, as the surface conditions and availability of water on Mars make it arguably the most hospitable planet in the solar system other than Earth. While the Moon has been proposed as the first location for human colonization, unlike Earth's moon, Mars has an atmosphere, giving it the potential capacity to host human and other organic life. The possibility of colonizing Mars has captured the popular imagination in science and science-fiction.

Interplanetary spaceflight

Mars requires less energy per unit mass (delta V) to reach from Earth than any planet except Venus. Using a Hohmann transfer orbit, a trip to Mars requires approximately nine months in space. Modified transfer trajectories that cut the travel time down to seven or six months in space are possible with incrementally higher amounts of energy and fuel compared to a Hohmann transfer orbit, and are in standard use for robotic Mars missions. Shortening the travel time below about six months requires higher delta-v and an exponentially increasing amount of fuel, and is not feasible with chemical rockets, but could become feasible with advanced spacecraft propulsion technologies not in current use, such as VASIMR, and nuclear rockets, the latter of which could potentially cut the trip time down to about two weeks. Another possibility is constant-acceleration technologies such as solar sails or ion drives which permits passage times at close approaches on the order of several weeks. Both of these are currently feasible and could readily obtain a constant acceleration of 0.1g.