Trans-Neptunian object
A Trans-Neptunian object (TNO) is any object in the solar system with all or most of its orbit beyond that of Neptune. The Kuiper belt and Oort cloud are names for some subdivisions of that volume of space. Pluto is a trans-Neptunian object, and if it had been discovered today, it might not have been called a planet. Another of the named trans-Neptunian Objects is Varuna. In July 2001 Ixion was discovered, half the size of Pluto. In October 2002 an object even larger than Ixion was discovered, named Quaoar.
Gravity, the attracting force between all matter, also attracts planets. Due to the changes in the orbits of the known planets in the early 1900s, it was assumed that there was one or more planets beyond Neptune, but not yet identified. This search for these led to the discovery of Pluto, and since then a few other significant objects have been found. These are still too small to explain the perturbations, though, and revised estimates of Neptune's mass showed that the problem was fictitious.
The hypothetical companion star Nemesis would have fallen under the definition of trans-Neptunian object, but it appears that no such star actually exists.
Some kinds of TNOs: Plutinos, cubewanos, scattered disk objects.
Transneptunian objects of note:
See also: Oort cloud, Kuiper belt
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Referenced By
1000km | 1 E6 m | 1e6 m | 1e6 metres | 2002 LM60 | 50000 Quaoar | Asteriod | Asteroid | Astronomical body | Astronomical object | Charon (moon) | Cubewano | Jovian planet | Jovian system | List of astronomical topics | List of astronomical topics (N-Z) | Luna | Miller-Urey experiment | Miller experiment | Minor planet | Moon | Planetary system | Quaoar | Quaoar (deity) | Scattered Disk Object | Solar System | Stanley Miller | Terrestrial planet | Terrestrial planets | Urey-Miller experiment
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