Kuiper Belt – Objects, Location, Facts

Kuiper Belt vs Oort Cloud
The Kuiper belt is a ring of ice bodies beyond the orbit of Neptune, including dwarf planets and comets.

The Kuiper belt is a donut-shaped region beyond the orbit of Neptune that contains dwarf planets, comets, and other icy bodies. Collectively, these bodies are Kuiper Belt Objects (KBOs) or Trans-Neptunian Objects (TNOs). The Kuiper belt starts at 30 astronomical units (AU) from the Sun and extends out to around 50 AU. Astronomers hypothesize that a vast spherical bubble called the Oort cloud extends beyond the Kuiper belt. But, the Oort cloud likely has a disc-shaped component, too.

  • The Kuiper belt is a thick ring of dwarf planets, comets, and debris out past the orbit of Neptune.
  • The belt contains around one hundred thousand objects that are at least 100 kilometers wide and countless smaller bodies. But, even the largest dwarf planet in the Kuiper belt is smaller than Earth’s Moon.
  • Like the asteroid belt, the Kuiper belt contains remnants from early solar system formation.

History and Naming

The Kuiper belt takes its name from Dutch astronomer Gerard Kuiper. However, Kuiper neither discovered the belt nor predicted its existence. American astronomer Frederick C. Leonard first proposed the existence of a group of bodies beyond Neptune shortly after Clyde Tombaugh’s discovery of Pluto in 1930. American astronomer Armin O. Leuschner also postulated that Pluto was only one of many objects further out in the solar system. But, scientists did not have direct evidence for the existence of the Kuiper belt until the discovery of minor planet Albion in 1992 and the comet-like body 5145 Pholus that same year. Since then, other large bodies and a host of centaurs (bodies that may become comets) have been identified.

The name “Kuiper belt” likely comes from a paper by Uruguayan astronomer Julio Fernández in which he speculated about a belt of comets located between 35 and 50 AU from the Sun. The first sentence of Fernández’s paper referred to both “Kuiper” and a “comet belt.” A Canadian team ran computer simulations to identify the origin of comets and referred to Fernández’s region between 35 and 50 AU as the “Kuiper belt”.

Major Bodies in the Kuiper Belt

While Pluto is the best-known resident of the Kuiper belt, it shares the region with many other bodies, called Kuiper Belt Objects or KBOs. There are countless KBOs, but the region is so vast they are actually very far apart from one another. So far, the objects consist of a mixture of rock and water, ammonia, and methane ice. Some of the dwarf planets have moons, which may have thin atmospheres. It is very cold and dark so far from the Sun, yet it is unknown whether or not these world support any life.

  • Comets: Comets come from both the Kuiper belt and the hypothetical Oort cloud. The biggest difference between comets from the two locations is that Kuiper belt comets have orbits within the plane of the solar system while comets from the Oort cloud orbit from any direction.
  • Pluto and its moons: Pluto is the largest known KBO. Because of it has a spherical shape and enough mass that it has cleared its orbit of debris, Pluto is a dwarf planet. The best known of Pluto’s moon are Charon, Nix, Styx, Kerberos, and Hydra.
  • Other dwarf planets: These include Orcus, Haumea, Quaoar, and Makemake. Salacia, Ixion, 2002 MS4, and 2002 AW197 are potential dwarf planets. Orcus has a large moon named Vanth. Haumea has a ring around it. Quaoar has a moon in synchronous orbit called Weywot. Eris and Sedna, while dwarf planets, are outside the Kuiper belt.
  • Planet Nine: While astronomers have not discovered Planet Nine (Planet 9), the disruption of orbits of other bodies suggests it exists. Estimates place the mass of Planet Nine as between five and ten times greater than that of the Earth.
  • Other large bodies: Bodies such as Huya and Lempo are sizeable, yet don’t meet the requirements for classification as dwarf planets.
  • Debris: There are many other smaller rocks, ice chunks, and dust particles.
  • Triton: Triton is one of Neptune’s moon and may be a captured KBO.


  • Brown, Michael E.; Pan, Margaret (2004). “The Plane of the Kuiper Belt”. The Astronomical Journal. 127 (4): 2418–2423. doi:10.1086/382515
  • Davies, John K.; McFarland, J.; Bailey, Mark E.; Marsden, Brian G.; Ip, W. I. (2008). “The Early Development of Ideas Concerning the Transneptunian Region“. In M. Antonietta Baracci; Hermann Boenhardt; Dale Cruikchank; Alessandro Morbidelli (eds.). The Solar System Beyond Neptune. University of Arizona Press.
  • Fernández, J.A. (1980). “On the existence of a comet belt beyond Neptune”. Monthly Notices of the Royal Astronomical Society. 192 (3): 481–491. doi:10.1093/mnras/192.3.481
  • Morbidelli, Alessandro; Nesvorny, David (2020). “Kuiper belt: formation and evolution”. The Trans-Neptunian Solar System. ISBN 9780128164907. doi:10.1016/B978-0-12-816490-7.00002-3
  • Tancredi, G.; Favre, S. A. (2008). “Which are the dwarfs in the Solar System?”. Icarus. 195 (2): 851–862. doi:10.1016/j.icarus.2007.12.020
  • Trilling, D. E.; Bryden, G.; et al. (February 2008). “Debris Disks around Sun-like Stars”. The Astrophysical Journal. 674 (2): 1086–1105. doi:10.1086/525514