planeetoiden

Planeetoiden is a term that has been used historically to refer to celestial bodies that orbit the Sun and are not comets. This classification has evolved over time as our understanding of the solar system has grown. Initially, the term was applied to objects that were observed to have a planetary appearance but were not among the known planets.

The most prominent group of objects historically referred to as planetoids are found in the asteroid belt, located between the orbits of Mars and Jupiter. These are rocky, airless worlds that are too small to be called planets. Ceres, the largest object in the asteroid belt, was once classified as a planet before the discovery of other asteroids, after which it was reclassified as a dwarf planet.

The term planetoid has also been used more broadly to encompass any minor planet or even trans-Neptunian objects. However, with the establishment of the International Astronomical Union (IAU) definition of a planet in 2006, the term has largely fallen out of common scientific usage. The IAU now categorizes celestial bodies into planets, dwarf planets, and small Solar System bodies. While planetoid is not an official IAU category, it remains a recognizable term in older astronomical literature and sometimes in popular science contexts.