Minor planet

Lore & Background

Historically, the terms asteroid, minor planet, and planetoid have been more or less synonymous, but this terminology became more complicated with the discovery of numerous minor planets beyond Jupiter, especially trans-Neptunian objects that are generally not considered asteroids. A minor planet seen releasing gas may be dually classified as a comet. Minor planets include asteroids such as near-Earth objects, Earth trojans, Mars trojans, Mars-crossers, main-belt asteroids, and Jupiter trojans, as well as distant minor planets like Uranus trojans, Neptune trojans, centaurs, and trans-Neptunian objects. Most distant minor planets reside in the Kuiper belt and the scattered disc. Objects are called dwarf planets if their own gravity is sufficient to achieve hydrostatic equilibrium and form an ellipsoidal shape; all other minor planets and comets are called small Solar System bodies. Naming of minor planets follows a three-step process: a provisional designation upon discovery, a formal number once the orbit is confirmed, and optionally a name.

Reader's Guide

Minor planets represent a vast and diverse population of Solar System bodies, bridging the gap between planets and comets. Their study has revealed the structure of the asteroid belt, the Kuiper belt, and the scattered disc, and has provided insights into the formation and evolution of the Solar System. With over 1.5 million known objects and hundreds of thousands more discovered each month, minor planets are crucial for understanding planetary dynamics, impact hazards, and the distribution of material in the Solar System. The discovery of distant minor planets like centaurs and trans-Neptunian objects has expanded the known boundaries of the Solar System and continues to challenge definitions of planetary bodies.

Did You Know?

• A minor planet seen releasing gas may be dually classified as a comet.