planetoid

Planetoid is a term used in astronomy to describe a small planetary body that orbits the Sun. Historically, planetoid referred to relatively small, planet-like bodies such as asteroids and dwarf planets, emphasizing their status as smaller constituents of the solar system rather than major planets. In modern usage, the term is not an official IAU category; the preferred terms are asteroid for most rocky inner-solar-system bodies and minor planet for any object orbiting the Sun that is not a comet or a spacecraft. The IAU uses minor planet as a broad designation, with subcategories including dwarf planets when objects meet specific criteria such as hydrostatic equilibrium and not having cleared their orbits.

Planetoids vary greatly in size, from tens of kilometers to hundreds of kilometers in diameter. They can be rocky, metallic, or icy, and many have satellites (moons). They are found throughout the solar system, from the asteroid belt between Mars and Jupiter to the outer regions of the Kuiper belt and scattered disk.

Historically associated with objects such as Ceres, Vesta, and Pallas, the term planetoid reflects an early view of these bodies as small, planet-like worlds. Pluto was at times referred to as a planetoid before its reclassification as a dwarf planet. Studying planetoid-sized bodies provides insights into solar-system formation and the materials present in the early solar system. Modern surveys and spacecraft missions continue to map and characterize these objects.