A Class D planetoid is a tiny world that generally does not meet the
criteria for a planet. This includes many moons, asteroids, and
small planet-like objects. Many are not even spherical, and have
eccentric orbits that are cluttered with various smaller rocks and
Dwarf planetoids generally lack the internal structure of larger
worlds; instead of having an inner-core, mantle, and crust, many
dwarf planetoids are simply composed of solid rock and ice
(however, some larger dwarfs, such as Pluto, do have a more
planet-like internal structure).
They are often rich in natural resources, making them ideal for
mining operations. However, most dwarf planetoids either have a
very tenuous atmosphere (usually composed of water vapor and
nitrogen) or more commonly, no atmosphere at all, making
pressure domes a requirement for colonization.