With Mars there's also that "step outside without a protective suit, suffocate and freeze to death in few minutes" bit: http://en.wikipedia.org/wiki/Atmosphere_

With Mars there's also that "step outside without a protective suit, suffocate and freeze to death in few minutes" bit: http://en.wikipedia.org/wiki/Atmosphere_of_Mars http://en.wikipedia.org/wiki/Atmosphere_of_Mars