Discrepancies in the early 1900s between the observed and expected orbits of Uranus and Neptune suggested that there were one or more additional planets beyond Neptune.
As of October 2020, the catalog of minor planets contains 678 numbered and more than 2,000 unnumbered TNOs. The first trans-Neptunian object to be discovered was Pluto in 1930.
The search for these led to the discovery of Pluto in February 1930, which was too small to explain the discrepancies.
Revised estimates of Neptune's mass from the Voyager 2 flyby in 1989 showed that the problem was spurious.
It took until 1992 to discover a second trans-Neptunian object orbiting the Sun directly, 15760 Albion.
Only after the 1992 discovery of a second TNO, 15760 Albion, did systematic searches for further such objects begin.
Eris, the most massive TNO, was discovered in 2005, revisiting a long-running dispute within the scientific community over the classification of large TNOs, and whether objects like Pluto can be considered planets.
For a long time, no one searched for other TNOs as it was generally believed that Pluto, which up to August 2006 was classified a planet, was the only major object beyond Neptune.
In December 2018, the discovery of , nicknamed "Farout", was announced.
One 2018 design study for an Interstellar Precursor, included a visit of minor planet 50000 Quaoar, in the 2030s. == Extreme trans-Neptunian objects == Among the extreme trans-Neptunian objects are three high-perihelion objects classified as sednoids: 90377 Sedna, , and 541132 Leleākūhonua.
As of October 2020, the catalog of minor planets contains 678 numbered and more than 2,000 unnumbered TNOs. The first trans-Neptunian object to be discovered was Pluto in 1930.
Overall this type of spacecraft studies have proposed a launch in the 2020s, and would try to go a little faster than the Voyagers using existing technology.
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Page generated on 2021-08-05