A trans-Neptunian object (TNO), also written transneptunian object, is any minor planet in the Solar System that orbits the Sun at a greater average distance than Neptune, which has an orbital semi-major axis of 30.1 astronomical units (au).
Orcus is a large trans-Neptunian object and likely dwarf planet located in the Kuiper belt, with one large moon, Vanth. It has an estimated diameter of 870 to 960 km, comparable to the Inner Solar System dwarf planet Ceres. Orcus had been accepted by many astronomers as a dwarf planet, though as of 2024 that classification remains somewhat controversial. The surface of Orcus is relatively bright with albedo reaching 23 percent, neutral in color, and rich in water ice. The ice is predominantly in crystalline form, which may be related to past cryovolcanic activity. Other compounds like methane or ammonia may also be present on its surface. Orcus was discovered by American astronomers Michael Brown, Chad Trujillo, and David Rabinowitz on 17 February 2004.
Michael E. Brown is an American astronomer, who has been professor of planetary astronomy at the California Institute of Technology (Caltech) since 2003. His team has discovered many trans-Neptunian objects (TNOs), including the dwarf planet Eris, which was originally thought to be bigger than Pluto, triggering a debate on the definition of a planet.
David Lincoln Rabinowitz is an American astronomer, discoverer of minor planets and researcher at Yale University.
Haumea is a dwarf planet located beyond Neptune's orbit. It was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory in the United States and disputably also in 2005 by a team headed by José Luis Ortiz Moreno at the Sierra Nevada Observatory in Spain. On September 17, 2008, it was named after Haumea, the Hawaiian goddess of childbirth, under the expectation by the International Astronomical Union (IAU) that it would prove to be a dwarf planet. Nominal estimates make it the third-largest known trans-Neptunian object, after Eris and Pluto, and approximately the size of Uranus's moon Titania.
Makemake is a dwarf planet and the second-largest of what is known as the classical population of Kuiper belt objects, with a diameter approximately that of Saturn's moon Iapetus, or 60% that of Pluto. It has one known satellite. Its extremely low average temperature, about 40 K (−230 °C), means its surface is covered with methane, ethane, and possibly nitrogen ices. Makemake shows signs of geothermal activity and thus may be capable of supporting active geology and harboring an active subsurface ocean.
(55565) 2002 AW197 (provisional designation 2002 AW197) is a classical, non-resonant trans-Neptunian object from the Kuiper belt in the outermost region of the Solar System, also known as a cubewano. With a likely diameter of at least 700 kilometers (430 miles), it is approximately tied with 2002 MS4 and 2013 FY27 (to within measurement uncertainties) as the largest unnamed object in the Solar System. It was discovered at Palomar Observatory in 2002.
A dwarf planet is a small planetary-mass object that is in direct orbit around the Sun, massive enough to be gravitationally rounded, but insufficient to achieve orbital dominance like the eight classical planets of the Solar System. The prototypical dwarf planet is Pluto, which for decades was regarded as a planet before the "dwarf" concept was adopted in 2006.
Eris is the most massive and second-largest known dwarf planet in the Solar System. It is a trans-Neptunian object (TNO) in the scattered disk and has a high-eccentricity orbit. Eris was discovered in January 2005 by a Palomar Observatory–based team led by Mike Brown and verified later that year. In September 2006, it was named after the Greco–Roman goddess of strife and discord. Eris is the ninth-most massive known object orbiting the Sun and the sixteenth-most massive overall in the Solar System. It is also the largest known object in the solar system that has not been visited by a spacecraft. Eris has been measured at 2,326 ± 12 kilometers (1,445 ± 7 mi) in diameter; its mass is 0.28% that of the Earth and 27% greater than that of Pluto, although Pluto is slightly larger by volume. Both Eris and Pluto have a surface area that is comparable to the area of Russia or South America.
(24835) 1995 SM55 (provisional designation 1995 SM55) is a trans-Neptunian object and member of the Haumea family that resides in the Kuiper belt, located in the outermost region of the Solar System. It was discovered on 19 September 1995, by American astronomer Nichole Danzl of the Spacewatch program at Kitt Peak National Observatory near Tucson, Arizona, in the United States. It measures approximately 200 kilometers in diameter and was the second-brightest known object in the Kuiper belt, after Pluto, until 1996 TO66 was discovered.
(120178) 2003 OP32, also written as (120178) 2003 OP32, is a trans-Neptunian object (TNO) that resides in the Kuiper belt. It was discovered on July 26, 2003 by Michael E. Brown, Chad Trujillo and David L. Rabinowitz at Palomar Mountain in California.
(145453) 2005 RR43 (provisional designation 2005 RR43) is a trans-Neptunian object (TNO) estimated to be about 250 km in diameter. It was discovered on 9 September 2005 by Andrew Becker, Andrew Puckett and Jeremy Kubica at Apache Point Observatory in Sunspot, New Mexico.
(120348) 2004 TY364, provisionally known as 2004 TY364, is a trans-Neptunian object. It is an inner classical Kuiper belt object in the definition by Gladman, Marsden, and Van Laerhoven (e<0.24). Its inclination of almost 25 degrees disqualifies it as such in Marc Buie's definition. It is also not listed as a scattered disc object by the Minor Planet Center. It was discovered by Michael E. Brown, Chad Trujillo and David L. Rabinowitz on October 3, 2004 at the Palomar Observatory.
(202421) 2005 UQ513 (provisional designation 2005 UQ513) is a cubewano with an absolute magnitude of 3.97. Its spectrum has a weak signature of absorption by water ice. Like Quaoar, it has a very red spectrum, which indicates that its surface probably contains many complex, processed organic molecules. Its light curve shows variations of Δm=0.3 mag, but no period has been determined.
The dwarf planet Haumea has two known moons, Hiʻiaka and Namaka, named after Hawaiian goddesses. These small moons were discovered in 2005, from observations of Haumea made at the large telescopes of the W. M. Keck Observatory in Hawaii.
The Haumea or Haumean family is the only identified trans-Neptunian collisional family; that is, the only group of trans-Neptunian objects (TNOs) with similar orbital parameters and spectra that suggest they originated in the disruptive impact of a progenitor body. Calculations indicate that it is probably the only trans-Neptunian collisional family. Members are known as Haumeids.
Haumea was the first of the IAU-recognized dwarf planets to be discovered since Pluto in 1930. Its naming as a dwarf planet was delayed by several years due to controversy over who should receive credit for its discovery. A California Institute of Technology (Caltech) team headed by Michael E. Brown first noticed the object, but a Spanish team headed by José Luis Ortiz Moreno were the first to announce it, and so normally would receive credit. Brown accused the Spanish team of fraud, using Caltech observations without credit to make their discovery, while the Ortiz team accused the American team of political interference with the International Astronomical Union (IAU). The IAU officially recognized the Californian team's proposed name Haumea over the name proposed by the Spanish team, Ataecina, in September 2008.
Gonggong is a dwarf planet, a member of the scattered disc beyond Neptune. It has a highly eccentric and inclined orbit during which it ranges from 34–101 astronomical units from the Sun. As of 2019, its distance from the Sun is 88 AU, and it is the sixth-farthest known Solar System object. According to the Deep Ecliptic Survey, Gonggong is in a 3:10 orbital resonance with Neptune, in which it completes three orbits around the Sun for every ten orbits completed by Neptune. Gonggong was discovered in July 2007 by American astronomers Megan Schwamb, Michael Brown, and David Rabinowitz at the Palomar Observatory, and the discovery was announced in January 2009.
