Minor planet
A Sun-orbiting body that is neither a planet nor a comet.
A minor planet is an astronomical object in direct orbit around the Sun that is exclusively classified as neither a planet nor a comet, according to the International Astronomical Union (IAU). This definition was refined in 2006, when the IAU reclassified such objects into two new categories: dwarf planets and small Solar System bodies. Prior to this, the term "minor planet" was the official designation for these bodies, which historically included objects like Ceres—discovered in 1801 and initially called a planet, then an asteroid—and Pluto, which was generally not considered a minor planet. The term "minor planet" itself was introduced in 1841 and was considered a subcategory of "planet" until 1932. The terms asteroid, minor planet, and planetoid have been used more or less synonymously, though the discovery of many objects beyond Jupiter, especially trans-Neptunian bodies, complicated this terminology. A minor planet that releases gas may be dually classified as a comet. The key distinction from the eight official planets is that all minor planets fail to clear their orbital neighborhood. The IAU stated that while the term minor planet may still be used, "small Solar System body" is preferred. However, for numbering and naming purposes, the traditional distinction between minor planet and comet remains. Minor planets include a wide range of populations: asteroids (such as near-Earth objects, Mars-crossers, main-belt asteroids, and Jupiter trojans), as well as distant minor planets like centaurs, Neptune trojans, and trans-Neptunian objects found in the Kuiper belt and 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 small Solar System bodies.
- Known or suspected dwarf planets among n
- Approximately nine
- Governing body
- International Astronomical Union (IAU)
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.
Frequently Asked Questions
What are Minor planet's powers/role?
Minor planets act as the Solar System's residual building blocks, preserving pristine material from the original protoplanetary disk. They also populate the gaps between the major planets and beyond Neptune, giving astronomers a dense population to study for orbital dynamics and compositional clues.
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