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TNOs or Trans-Neptunian Objects

Largest TNOs or Trans-Neptunian Objects


A Trans-Neptunian Object (TNO) is a minor planet that orbits the Sun at a greater distance than Neptune, or 30 AU. Above is an artist's depiction of the eight largest known TNOs and their moons, with the Earth at the bottom. The first TNO to be discovered was Pluto in 1930, which was considered a planet until August 24, 2006, when the increasing discoveries of larger and comparably-sized TNOs brought about Pluto's demotion from planet to dwarf planet and/or TNO.

The TNO Eris—named after the Greek goddess of strife and discord—is the largest known dwarf planet and ninth largest body orbiting the Sun. With an orbit inclined 44° to the ecliptic, her daughter and moon Dysnomia are appropriately named for the demon of lawlessness. Eris and its moon are the most distant known solar system objects other than Sedna and a few comets. First spotted in 2003, Eris was not then identified as a solar system object because the software excluded objects moving slower than 1.5''/hr. When Sedna was discovered later that year moving at only 1.75''/hr., the old data was reexamined by eye and Eris’ slower (0.8''/hr.) motion was noticed.

TNOs are currently classified into two groups based on their distance from the Sun and their orbital characteristics. These are:

1) Classical Kuiper Belt Objects (KBOs) with orbits from 30 - 55 AU from the Sun that are nearly circular and have small inclinations to the ecliptic. Pluto, Quaoar and Makemake are KBOs.

2) Scattered Disk Objects (SDOs) that are usually further from the Sun and have very irregular orbits (believed to be caused by the "scattering" of the gas giants and continued perturbation by Neptune), such as Eris and Sedna.

As of July 2014 there were more than 1,500 Trans-Neptunian Objects on the Minor Planet Center's List of TNOs, of which 1352 have a perihelion beyond Neptune's orbit. And as of November 2009 over 200 of these had orbits that were so well known that they had been given a permanent designation as a "minor planet".



The table below displays orbital elements for the 8 largest TNOs.


Orbital elements table, largest TNOs




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© Carl Woebcke: TNOs: The Largest Trans-Neptunian Objects, 1991-2017. All rights reserved.