Separates the "Inner planets ", ( Mercury, Venus, Earth, Mars), from the "Outer planets ", ( Jupiter, Saturn, Uranus, Neptune).
There are a few bodies in the asteroid belt, like Ceres or Vesta that are big enough to paraterraform, as in to create artificial biospheres on. Disadvantages are many, including low gravity, and little protection from cosmic radiation (though building colonies underground may solve this). A different approach which would also solve the low gravity problem is hollowing out the asteroid, spinning it on an axis to create centrifugal force, and inhabiting the inside. Filled with air, and given a light source by either reflecting sunlight from outside or some sort of fusion technology, these asteroid habitats could easily support micro-ecosystems and thousands of humans.
The emerging asteroid mining industry may provide the volatiles, fuel, and raw material needed to make terraforming or, any other type of space colonization possible. Larger asteroids can also serve as waystations between the planets, where water ice is mined, converted into rocket fuel.