EXPLORE


JOINRENEWJOIN

Give a Gift Membership
  

Space Topics

Trans-Neptunian Objects


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, Makemake, 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, Eris (formerly known as 2003 UB313). Eris' discovery ignited a fierce debate about the definition of a planet. According to the new definition from the IAU, none of the trans-Neptunian objects is a planet, but three are considered dwarf planets: Pluto, Eris, and Makemake.

Although both Voyager spacecraft have traveled beyond the main region of the Kuiper belt, neither targeted any trans-Neptunian objects. Trans-Neptunian objects have only been studied through the use of Earth-based and Earth-orbiting observatories. Finally, however, the New Horizons mission is en route toward Pluto and its moons. After the Pluto encounter in 2015, plans call for New Horizons to travel onward to at least two Kuiper belt objects within 5 to 10 years. The Kuiper belt objects to be visited by New Horizons will be small ones, and have not yet been discovered; a search will begin a few years before the Pluto encounter.