"The Richness of Our Solar System"
(c) 2011 by Jordan S. Bassior
Most people, including most people who are in favor of human expansion beyond the Earth, don't realize just how rich is the Solar System. They tend to look only at the major terrestrial planets and assume that the only place into which we can expand without interstellar travel is Mars, because there are only three such planets in our Solar System aside from our own Terra, and Mars is the only one of these major terrestrial planet not to be far too hot (Mercury and Venus) for convenient colonization.
But even if we only limit ourselves to non gas-giant worlds large enough to be forced into globular objects under their own gravity, and have some internal differentiation (for ease of access to ores), there are many others just in our Solar System: not only Mercury, Venus and Mars, but also Luna, Ceres, Vesta, Callisto, Ganymede, Europa, Io, Titan, Triton, Pluto, Charon and Eris. That's fifteen other terrestrial worlds in our Solar System, and I'm deliberately setting a high standard for "terrestrial world" -- I could set the bar a bit lower and add several other asteroids, moons and Kuiper Belt Objects.
The habitability of these objects of course varies (from Mars all the way down to Venus) and certain of these worlds have significant environmental challenges (radiation on the three inmost Galilean moons of Jupiter, cold on the three outmost Galilean moons of Jupiter and all the worlds farther out from the Sun, heat on Mercury and Venus). But none are beyond the capabilities of our current physical science to colonize, and all are large enough worlds that there are certain to be valuable lodes of various minerals to attract our greed, and many mysteries to excite our minds.
The future is bright, for those who care to open their eyes and look beyond the current mess on Earth.