As Saskboy pointed out in his comment on my post about the “10th Planet” that’s in the news today, other objects have been found beyond the orbit of Neptune besides Pluto and Xena. He mentions Quaoar, but that’s just the tip of the iceberg (or a fraction of the iceball, if you prefer). From the website of The Planetary Society:
Beyond the orbit of Neptune lurk millions of icy bodies. The trans-Neptunian objects are members of the solar system like the planets and asteroids, but are too small and distant to have been detected until very recently. Pluto was the first trans-Neptunian object to be discovered in 1930. Following Pluto’s discovery, scientists developed theories about populations of icy objects — like the Kuiper belt, scattered disk, and Oort Cloud — that orbit beyond Neptune and could be the source region for comets.
Since 1992, nearly a thousand trans-Neptunian objects have been observed. A few of these have acquired names, such as Chaos, Deucalion, Huya, Ixion, Orcus, Quaoar, Rhadamanthus, Sedna, and Varuna. Other, equally interesting objects lack names and are known only by provisional designations like 1992 QB1. Many trans-Neptunian objects are binaries — two bodies with similar masses that orbit each other. Pluto and Charon form one such binary system. Recently, scientists discovered the first trans-Neptunian object known to be larger than Pluto, 2003 UB313.
