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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. 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. (See Planet X.) 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.
Trans-Neptunian objects of note:
- (15760) 1992 QB1, a cubewano
- (15874) 1996 TL66 , a scattered disk object
- 90482 Orcus, a plutino
- Charon, the moon of Pluto
- 28978 Ixion28978 Ixion ("ik SIGH un", sometimes "ICK see un") is a Kuiper belt object discovered on May 22, 2001 with a diameter of approximately 1055 km and a semimajor axis of about 39. Ixion is a Plutino: it has a 3:2 orbital resonance with Neptune. 28978 Ixion O, a plutino
- Pluto, considered a planet for historical reasons
- 50000 QuaoarThis article is about the trans-Neptunian object. For the Tongva god, see Quaoar (deity). 50000 Quaoar ( /"kwA o Ar/) is a Trans-Neptunian object orbiting the Sun in the Edgeworth- Kuiper belt. It was discovered on June 4, 2002 by astronomers Chadwick A., a cubewano
- 20000 VarunaTrans-Neptunian objects 20000 Varuna ("VAIR uh nuh") is a Kuiper Belt object about 1060 kilometers in diameter, estimated from a combination of thermal and optical measurements. Varuna Orbital characteristics Orbit type Kuiper belt Semimajor axis 43., a cubewano
- 90377 Sedna90377 Sedna is a Trans-Neptunian object discovered by Mike Brown ( Caltech), Chad Trujillo ( Gemini Observatory) and David L. Rabinowitz ( Yale University) on November 14, 2003. Its discovery was the farthest distance at which any natural object in the so
The hypothetical companion star Nemesis would have fallen under the definition of trans-Neptunian object, but it appears that no such star actually exists.
A fuller list of objects is being compiled in the list of trans-Neptunian objects.
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Trans-Neptunian objects
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