"I submit that Mars is the 21st-century destination for humans. There are plenty of reasons why going to Mars makes sense. Mars has a 24.5-hour day, compared to the two weeks of day and two weeks of night on the moon - an abomination for the human circadian rhythm. Mars is more Earthlike in other ways: It has twice the moon's gravitational force, is farther from the sun, and hence it presents less of a radiation risk; it once held liquid water seas and still holds water ice in the polar ice caps ( the moon MAY have some ice frozen in permanently shaded craters, but this would be extremely costly to mine); it has a thin CO2 atmosphere that can be used for processing breathable air and rocket fuel. If you're looking for a new place in the solar system for people to live, Mars is much better than the moon. . . . [W]e will need to choose between two main mission architectures: a "slow-boat" three-year mission, using conventional rockets, or a "fast-track" six- to nine-month mission using advanced electric propulsion engines. . . . ([F]ast track is the right answer . . . .)"