An Asteroid and Comet Habitat is an interplanetary habitat formed by hollowing out asteroids or comets and rotating them so that artificial gravity can be generated within the habitat themselves.
Overview
In most early stages of interplanetary colonization, species who have not yet discovered Warp Drive capabilities are left with limited options on planetary bodies to colonize. As most planetary systems have some kind of asteroid belt, Oort Cloud or some belt of planetary debris left over from the formation of the star system, these rocky bodies are ideal for early interplanetary civilizations to colonize due to the fact that the outer surface of the asteroid or comet can protect the inner habitat from impacts or from solar radiation from the parent star.
For humans, the first habitat of such a nature was carved out in the year 2210 using Mars' moon Phobos. The second was Deimos. From these two habitats, the terraforming of Mars was spearheaded and eventually both became major historical sites in the Sol System.