planetoids

Planetoid is a term used in astronomy to describe small planetary bodies that orbit a star. Historically it referred to objects that are not fully formed planets but are large enough to be considered planetary in nature. In modern usage the term is imprecise; standard classifications use "asteroid" for small rocky bodies, "dwarf planet" for sufficiently large bodies that are nearly spherical, and "minor planet" for many small bodies that do not meet the criterion for a planet.

Planetoids can be found throughout the solar system. The largest and most numerous are in the main asteroid belt between Mars and Jupiter, but they also occur among the Kuiper Belt and beyond. They vary widely in size, from meters across to objects hundreds of kilometers in diameter. Composition ranges from rocky and metallic to icy.

Notable planetoids include Ceres, the largest object in the asteroid belt and a dwarf planet; Vesta, Pallas, and Hygiea; plus numerous trans-Neptunian objects and dwarf planets such as Pluto, Eris, Haumea, and Makemake. Collectively they provide clues about the early solar system and planetary formation.

The term "planetoid" is less commonly used in formal classifications today, having largely been superseded by "minor planet" and by specific designations such as asteroid or dwarf planet.