A planet is defined by the Encyclopaedia Cosmosica as "a celestial body that orbits around a star, has adequate mass to achieve hydrostatic equilibrium (i.e. a spherical form), and has 'cleared the neighbourhood' around its orbit." A "dwarf planet" is a non-satellite body that fulfills only the first two of these criteria. A "planetoid" fulfills only the first. A "nomad planet" is a planetary-mass body that has either strayed out of its star system or was never gravitationally bound to one.
Earth is the Inspector's favourite planet, although his mysterious mission requires him to travel to numerous ones across the universe. The rediscovery of a planetoid intersecting Earth's orbit is a plot point in "The Lost Asteroid" serial. Kayaclasch is technically a nomad planet since its planetary system lacks a star and is kept in stasis only through the vast and awe-inspiring technology of the Infinity Knights.