[troutman]

Humans would face big challenges on Mars - it is very cold, IIRC gravity is 1/3 that of Earth, and radiation levels are extreme.

http://en.wikipedia.org/wiki/Manned_mission_to_Mars

There are several key challenges that a human mission to Mars must overcome:

1. physical effects of exposure to high-energy cosmic rays and other ionizing radiation.[2][3]
2. physical effects of a prolonged low-gravity environment, including eyesight loss.[4][5][6]
3. physical effects of a prolonged low-light environment.
4. psychological effects of isolation from Earth.
5. psychological effects of lack of community due to lack of real-time connections with Earth.
6. social effects of several humans living under crowded conditions for over one Earth year.
7. inaccessibility of terrestrial medical facilities.