Trans-Neptunian object

A body in the Solar System whose orbit lies partly or wholly beyond Neptune’s orbit. Trans-Neptunian objects include dwarf planets, resonant bodies, and distant icy populations.

Kuiper belt: A region beyond Neptune containing many small icy bodies, including resonant and classical objects. Its populations make up the best-known concentration of trans-Neptunian objects.
Pluto: A dwarf planet in the Kuiper belt with a large moon, Charon, and an eccentric, resonant orbit. Pluto is the largest known trans-Neptunian object and the first discovered.
Planetary migration: The process by which a planet's orbit changes over time through gravitational interactions with other bodies. Neptune's migration could have captured and rearranged objects in the Kuiper belt.
New Horizons: A NASA spacecraft that flew past Pluto in 2015 and Arrokoth in 2019. Its encounters revealed surface geology and composition at two trans-Neptunian objects.
Planet Nine: A hypothetical distant planet proposed to explain the clustering of some extreme trans-Neptunian orbits. Its existence remains debated, and the proposed evidence comes from distant objects.
Scattered disc: A distant population of icy bodies on eccentric orbits altered by interactions with Neptune. Its objects occupy some of the most elongated orbits among trans-Neptunian populations.
Eris: A dwarf planet in the scattered disc, discovered in 2005, with a moon named Dysnomia. Its discovery helped prompt the formal definition of a planet.
Scattering (astronomy): A change in an object's orbit caused by gravitational encounters with another body. Repeated encounters with Neptune can place icy bodies on distant, eccentric paths.
Occultation (astronomy): An event in which one celestial body passes in front of another from an observer's viewpoint. Stellar occultations can measure the sizes and shapes of small distant objects.
Oort cloud: A hypothesized vast, roughly spherical reservoir of icy bodies surrounding the Solar System. It may connect the most distant trans-Neptunian populations to long-period comets.

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