Mars is indeed an attractive place to consider building a space
colony. Its thin - but not virtually nonexistent - atmosphere, though,
complicates landing on it. And while it has most of the elements
needed for permanent habitation, nitrogen is in very short supply.

One body in our Solar System that has water ice, methane, and ammonia
in abundance, as well as rock, is the former planet Pluto. Since it is
no longer called a planet, though, it will be psychologically
perceived as less important.

Of course, Pluto is so far away that we will first have to perfect
life-support in space by attaining Mars.

John Savard