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The IAU’s preferred broad category is “small Solar System body,” with “minor planet” still usable but less preferred.
Asteroid terminology and classification covers how these objects are named and how they are distinguished from related small bodies such as comets and other “small Solar System bodies.” The International Astronomical Union (IAU) introduced the broad term “small Solar System body” for objects that are not planets, dwarf planets, or natural satellites, which includes asteroids, comets, centaurs, trojans, and trans-Neptunian objects. Historically, the first discovered asteroid (Ceres) was initially treated as a planet, and the term “asteroid” was proposed by William Herschel; it comes from Greek roots meaning “star-like” or “star-shaped,” reflecting how early telescopic observations showed these objects as star-like points that moved. In classification, an object is generally treated as an asteroid (rather than a comet) if it does not develop a coma/tail when warmed by solar radiation. The main difference is that comets show activity due to sublimation of near-surface ices, while asteroids are typically rocky, metallic, or icy bodies without an atmosphere. However, observations suggest a continuum between asteroids and comets rather than a strict boundary. Asteroids are also commonly grouped by spectral/physical type—broadly C-type (carbonaceous), M-type (metallic), and S-type (silicaceous)—and are often restricted in usage to “classical asteroids” such as main-belt asteroids, Jupiter trojans, and near-Earth asteroids, rather than all minor planets beyond Jupiter.
The IAU’s preferred broad category is “small Solar System body,” with “minor planet” still usable but less preferred.
Asteroids are distinguished from comets by the presence of coma/tail activity: comets show activity when warmed, while asteroids generally do not.
Asteroids are commonly classified into spectral types such as C-type (carbonaceous), M-type (metallic), and S-type (silicaceous).
The distinction between asteroids and comets is increasingly viewed as a continuum rather than a sharp dividing line.
An IAU broad category for objects in the Solar System that are neither planets nor dwarf planets nor natural satellites, including asteroids and comets.
A historical term for small Solar System objects; the IAU notes it may still be used, though “small Solar System body” is generally preferred.
A minor planet that does not show cometary coma/tail activity when warmed by solar radiation and is typically rocky, metallic, or icy.
A cloud around a comet’s nucleus produced by sublimation of near-surface ices when heated by solar radiation.
A carbonaceous asteroid spectral class, generally associated with carbon-rich compositions.
A metallic asteroid spectral class, generally associated with metal-rich compositions.
A silicaceous (stony) asteroid spectral class, generally associated with silicate-rich compositions.
The idea that observational evidence blurs the boundary between asteroid-like and comet-like bodies rather than separating them sharply.
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