Trans-Neptunian object

A trans-Neptunian object (TNO) is any object in the solar system which orbits the sun at a greater distance on average than Neptune. The Kuiper belt, Scattered disk, and Oort cloud are names for three divisions of this volume of space. Pluto and its moon Charon are trans-Neptunian objects, and if Pluto had been discovered today, it might not have been called a planet. (See the definition of Planet.)

Related Topics:
Solar system - Orbit - Neptune - Kuiper belt - Scattered disk - Oort cloud - Pluto - Charon - Planet - Definition of Planet

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The orbit of each of the planets is affected by the gravitational influences of all the other planets. Discrepancies in the early 1900s between the observed and expected orbits of the known planets suggested that there were one or more additional planets beyond Neptune (see Planet X). The search for these led to the discovery of Pluto, and since then a few other significant objects have been found. These were too small to explain the discrepancies, however, and revised estimates of Neptune's mass showed that the problem was spurious.

Related Topics:
Gravitational - 1900s - Planet X

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