Haumea in the context of "Moons of Haumea"

The Kuiper belt (/ˈkaɪpər/ ) is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times as wide and 20–200 times as massive. Like the asteroid belt, it consists mainly of small bodies or remnants from when the Solar System formed. While many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia, and water. The Kuiper belt is home to most of the objects that astronomers generally accept as dwarf planets: Orcus, Pluto, Haumea, Quaoar, and Makemake. Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, may have originated in the region.

The Kuiper belt is named in honor of the Dutch astronomer Gerard Kuiper, who conjectured the existence of a version of the belt in 1951. There were researchers before and after him who proposed similar hypoetheses, such as Kenneth Edgeworth in the 1930s. The most direct prediction of the belt was by astronomer Julio Ángel Fernández, who published a paper in 1980 suggesting the existence of a comet belt beyond Neptune which could serve as a source for short-period comets.

Charon (/ˈkɛərɒn, -ən/ KAIR-on, -⁠ən or /ˈʃærən/ SHARR-ən), formal designation (134340) Pluto I, is the largest of the five known natural satellites of the dwarf planet Pluto. It has a mean radius of 606 km (377 mi). Charon is the sixth-largest known trans-Neptunian object after Pluto, Eris, Haumea, Makemake, and Gonggong. It was discovered in 1978 at the United States Naval Observatory in Washington, D.C., using photographic plates taken at the United States Naval Observatory Flagstaff Station (NOFS).

With half the diameter and one-eighth the mass of Pluto, Charon is a very large moon in comparison to its parent body. Its gravitational influence is such that the barycenter of the Plutonian system lies outside Pluto, and the two bodies are tidally locked to each other. The dwarf planet systems Pluto–Charon and Eris–Dysnomia and the dwarf planet candidate system Salacia-Actaea are the only known examples of mutual tidal locking in the Solar System, though it is likely that Orcus–Vanth is another.

The number of dwarf planets in the Solar System is unknown. Estimates have run as high as 200 in the Kuiper belt and over 10,000 in the region beyond.However, consideration of the surprisingly low densities of many large trans-Neptunian objects, as well as spectroscopic analysis of their surfaces, suggests that the number of dwarf planets may be much lower, perhaps only nine among bodies known so far. The International Astronomical Union (IAU) defines dwarf planets as being in hydrostatic equilibrium, and notes six bodies in particular: Ceres in the inner Solar System and five in the trans-Neptunian region: Pluto, Eris, Haumea, Makemake, and Quaoar. Only Pluto and Ceres have been confirmed to be in hydrostatic equilibrium, due to the results of the New Horizons and Dawn missions. Eris is generally assumed to be a dwarf planet because it is similar in size to Pluto and even more massive. Haumea and Makemake were accepted as dwarf planets by the IAU for naming purposes and will keep their names if it turns out they are not dwarf planets. Smaller trans-Neptunian objects have been called dwarf planets if they appear to be solid bodies, which is a prerequisite for hydrostatic equilibrium: planetologists generally include at least Gonggong, Orcus, and Sedna. Quaoar was labelled as a dwarf planet in a 2022–2023 annual report, though it does not appear to be in hydrostatic equilibrium. In practice the requirement for hydrostatic equilibrium is often loosened to include all gravitationally rounded objects, even by the IAU, as otherwise Mercury would not be a planet.

Hiʻiaka, formal designation (136108) Haumea I, is the larger, outer moon of the trans-Neptunian dwarf planet Haumea. Discovered by Michael E. Brown and the Keck Observatory adaptive optics team on 26 January 2005, it is named after Hiʻiaka, the patron goddess of the Big Island of Hawaii and one of the daughters of Haumea. The moon follows a slightly elliptical orbit around Haumea every 49.5 days, at a distance of 49,400 km (30,700 mi).

Hiʻiaka is an elongated and irregularly shaped body with a mean diameter of 369 km (229 mi), making it the sixth-largest known moon of a trans-Neptunian object. It has a very low bulk density between 0.46 g/cm and 0.69 g/cm, which indicates it is mostly made of loosely-packed water ice and rock. Telescope observations have shown that Hiʻiaka has a highly reflective surface made of crystalline water ice, much like Haumea itself. Hiʻiaka rotates about its axis every 9.68 hours, and appears to rotate sideways with respect to its orbit around Haumea. Like its smaller sibling moon Namaka, Hiʻiaka is believed to be a fragment of Haumea that was ejected in the aftermath of a giant impact 4.4 billion years ago.

Namaka (full designation (136108) Haumea II) is the smaller, inner moon of the trans-Neptunian dwarf planet Haumea. Discovered by Michael E. Brown and the Keck Observatory adaptive optics team in the fall of 2005, it is named after Nāmaka, a water spirit and one of the daughters of Haumea in Hawaiian mythology. Namaka follows a highly elliptical orbit that is highly tilted by roughly 13 degrees with respect to Haumea's equator. Namaka is heavily perturbed by both the gravitational influence of Haumea's larger, outer moon Hiʻiaka and the variable gravitational field of Haumea's elongated shape.

With a diameter of around 150 km (93 mi), Namaka is predicted to have an irregular shape and a chaotic rotation. It has a reflective surface made of fresh water ice, similar to that of Haumea and Hiʻiaka. Like Hiʻiaka, Namaka is believed to be a fragment of Haumea that was ejected in the aftermath of a giant impact 4.4 billion years ago.

The following is a list of Solar System objects by orbit, ordered by increasing distance from the Sun. Most named objects in this list have a diameter of 500 km or more.

• The Sun, a spectral class G2V main-sequence star
• The inner Solar System and the terrestrial planets
  • Mercury
    • Mercury-crossing minor planets
  • Venus
    • Venus-crossing minor planets
      • Zoozve, Venus' quasi-satellite
  • Earth
    • Moon
    • Near-Earth asteroids
      • 2021 PH27
      • Apophis
      • Eros
    • Earth trojans (2010 TK7)
    • Earth-crosser asteroids
      • Earth's quasi-satellites
  • Mars
    • Deimos
    • Phobos
    • Mars trojans
    • Mars-crossing minor planets
  • Asteroids in the asteroid belt, between the orbits of Mars and Jupiter
    • Ceres, a dwarf planet
    • Vesta
    • Pallas
    • Hygiea
    • Europa (asteroid)
    • Davida
    • Sylvia
    • Asteroids number in the hundreds of thousands. For longer lists, see list of exceptional asteroids, list of asteroids, or list of Solar System objects by size.
      • Asteroid moons
  • A number of smaller groups distinct from the asteroid belt
• The outer Solar System with the giant planets, their satellites, trojan asteroids and some minor planets
  • Jupiter
    • Rings of Jupiter
    • Complete list of Jupiter's natural satellites
      • Galilean moons
        • Io
        • Europa (moon)
        • Ganymede
        • Callisto
    • Jupiter trojans
    • Jupiter-crossing minor planets
  • Saturn
    • Rings of Saturn
    • Complete list of Saturn's natural satellites
      • Mimas
      • Enceladus
      • Tethys (trojans: Telesto and Calypso)
      • Dione (trojans: Helene and Polydeuces)
      • Rhea
        • Rings of Rhea (largely disproven)
      • Titan
      • Hyperion
      • Iapetus
      • Phoebe
      • Shepherd moons
    • Saturn-crossing minor planets
  • Uranus
    • Rings of Uranus
    • Complete list of Uranus's natural satellites
      • Miranda
      • Ariel
      • Umbriel
      • Titania
      • Oberon
    • Uranus trojan (2011 QF99)
    • Uranus-crossing minor planets
  • Neptune
    • Rings of Neptune
    • Complete list of Neptune's natural satellites
      • Proteus
      • Triton
      • Nereid
    • Neptune trojans
    • Neptune-crossing minor planets
  • Non-trojan minor planets
    • Centaurs
      • Chiron
      • Chariklo
    • Damocloids
  • Trans-Neptunian objects (beyond the orbit of Neptune)
    • Kuiper-belt objects (KBOs)
      • Plutinos
        • Orcus, a dwarf planet
          • Vanth
        • Pluto, a dwarf planet
          • Complete list of Pluto's natural satellites
            • Charon
        • Ixion
        • Achlys
      • Twotinos
      • Cubewanos (classical objects)
        • Haumea, a dwarf planet
          • Namaka
          • Hiʻiaka
        • Quaoar, a dwarf planet
          • Weywot
        • Makemake, a dwarf planet
          • S/2015 (136472) 1
        • Máni
        • Salacia
          • Actaea
        • Aya
        • Varda
          • Ilmarë
        • Varuna
        • Ritona
        • Arrokoth
    • Scattered-disc objects
      • Gonggong, a dwarf planet
        • Xiangliu
      • Eris, a dwarf planet
        • Dysnomia
      • Chiminigagua
      • (84522) 2002 TC302
      • (87269) 2000 OO67
      • 2015 TH367/V774104
    • Detached objects
      • (612911) 2004 XR190
      • 2012 VP113 (possibly inner Oort cloud)
      • Sedna, a dwarf planet (possibly inner Oort cloud)
    • Oort cloud (hypothetical)
      • Hills cloud/inner Oort cloud
      • Outer Oort cloud

2060 Chiron is a ringed small Solar System body in the outer Solar System, orbiting the Sun between Saturn and Uranus. Discovered in 1977 by Charles Kowal, it was the first-identified member of a new class of objects now known as centaurs—bodies orbiting between the asteroid belt and the Kuiper belt. Chiron is named after the centaur Chiron in Greek mythology.

Although it was initially called an asteroid and classified only as a minor planet with the designation "2060 Chiron", in 1989 it was found to exhibit behavior typical of a comet. Today it is classified as both a minor planet and a comet, and is accordingly also known by the cometary designation 95P/Chiron. More recently, a series of occultation events through the 2010s and early 2020s revealed that Chiron hosts rings, making it one of four minor planets known to have rings (the three others being 10199 Chariklo, Haumea, and Quaoar) and the only known comet to do so.