Kuiper-belt objects (blue) with the sun and giant planets marked. Distances, but not sizes, are to scale.
10 April 2023
The Kuiper belt is the region of the solar system beyond Neptune ranging from 30 to 50 astronomical units (AU, an AU is some 93 million miles, or 150 million kilometers, equivalent to the distance from the Earth to the Sun.) The Kuiper belt is the region of origin for the short-period comets, i.e., those that take less than 200 years to orbit the sun. The belt is named for astronomer Gerard Kuiper.
In 1943, astronomer Kenneth Edgeworth suggested that material from the primordial solar system might exist in the region beyond Neptune and such material might occasionally wander into the inner solar system. In 1951, Gerard Kuiper made a similar postulation, but believed that such primordial trans-Neptunian material no longer existed because Pluto, which he assumed was the size of Earth, would have cleared it out. Neither Edgeworth nor Kuiper provided any evidence for the existence of such a belt of material, only postulation. As a result, the name is something of a misnomer, as neither Edgeworth nor Kuiper were firm in their suggestions. And if anyone should get credit for the idea it should be Edgeworth. As a result, the region is sometimes referred to as the Edgeworth-Kuiper belt.
Kuiper belt was coined by three astronomers in 1988. Martin Duncan, Thomas Quinn, and Scott Tremaine created a mathematical model to characterize the behavior of the short-period comets and determined that they originated in a region beyond Neptune. The name first appears in an article in the journal Science on 18 March 1988, prior to the formal publication of their paper:
Ruling out the Oort cloud, the modelers next tried a belt of low-inclination comets near Neptune’s orbit. The idea dates back to a suggestion by Gerard Kuiper in 1951 that it would only be natural to find some debris from the formation of the solar system beyond Neptune.
[…]
There are hurdles yet for the “Kuiper belt.” One is finding a means of bringing comets from the belt into Neptune-crossing orbits, which is where they were at the beginning of the simulation.
The formal article by the trio was published in the Astrophysical Journal on 15 May 1988:
In this Letter we present the key results of a set of extensive numerical simulations of gravitational scattering of comets by the giant planets, designed to determine whether the most likely source of the SP [short-period] comets is the Oort cloud or the Kuiper belt.
[…]
To summarize, the SP comets cannot be produced by planetary scattering of comets from the Oort cloud, or any other isotropic parent population. A comet belt (the "Kuiper belt”) containing a fraction of an Earth mass and located in the outer parts of the solar system is plausible on cosmogonic grounds and appears to offer the most promising source for the SP comets, although the mechanisms by which the comets are supplied to planet-crossing orbits remains unclear.
Besides the comets, the Kuiper belt is home to at least eight larger objects that qualify for the status of dwarf planet. There are two other known dwarf planets in the solar system: Ceres in the asteroid belt and Sedna (see below), which orbits at a distance beyond the Kuiper belt and is the farthest known solar system object.
Pluto (see Pluto), discovered in 1930, is the most well-known of the Kuiper-belt objects.
Quaoar was the second Kuiper-belt object to be discovered. That was on 4 June 2002 by astronomers Chad Trujillo and Mike Brown. It is named for the creator spirit of the Tongva people, an Indigenous people of Southern California. Quaoar’s moon is Weywot, named for the deity’s son.
Sedna was discovered by Brown, Trujillo, and David Rabinowitz on 14 November 2003. It is the solar system object the farthest from the sun, that we know of. Technically, it is not a Kuiper belt object as it orbits beyond the belt but too close to be in the Oort cloud, ranging from 84 to 937 AU. In Inuit mythology, Sedna is the goddess of the sea and marine animals and the ruler of the Inuit underworld. Brown and his team suggested the name for her because of the planet’s cold temperature due to its distance from the sun.
Orcus was discovered on 17 February 2004 by Brown, Trujillo, and Rabinowitz and named for one of the Etruscan and Roman gods of the underworld, and in later Roman mythology he was conflated with Pluto.
Salacia probably qualifies as a dwarf planet, but too little is known about it to be sure. It was discovered by Henry Roe, Mike Brown, and Kristina Barkume on 22 September 2004. It was officially named in 2011 after a Roman goddess of the sea, the consort of Neptune.
Haumea has a contentious discovery, with two teams claiming that honor in 2004. Brown, Rabinowitz, and Trujillo discovered the planet on 28 December 2004 on images taken on 6 May 2004 and published the discovery online on 20 July 2005. A Spanish team, led by José Luis Ortiz Moreno found the planet on images taken in March 2003 and published the discovery on 27 July 2005. It later was revealed that the Spanish team had accessed Brown’s telescope observation logs prior to his announcement. Ortiz admitted to looking at Brown’s logs but only to search for images confirming his own discovery. In its naming announcement, the International Astronomical Union (IAU), which is responsible for officially naming celestial objects, did not credit either team, but the name chosen was one suggested by Brown. Haumea is the Hawaiian goddess of childbirth and fertility.
Eris is another one credited to Brown, Trujillo, and Rabinowitz, this time on 5 January 2005. The name Eris was proposed by Brown and accepted by the IAU on 14 September 2006. Eris is the Greek goddess of discord and strife. The planet Eris has a moon, named Dysnomia, after the daughter of the goddess Eris.
Makemake is yet another discovered by Brown, this time on 31 March 2005. Makemake is the Rapa Nui creator and fertility deity. The name was suggested by Brown and adopted by the International Astronomical Union (IAU) in July 2008. Brown said of the name:
We consider the naming of objects in the Solar System very carefully. Makemake's surface is covered with large amounts of almost pure methane ice, which is scientifically fascinating, but really not easily relatable to terrestrial mythology. Suddenly, it dawned on me: the island of Rapa Nui. Why hadn't I thought of this before? I wasn't familiar with the mythology of the island so I had to look it up, and I found Makemake, the chief god, the creator of humanity, and the god of fertility. I am partial to fertility gods. Eris, Makemake, and 2003 EL61 [i.e., Haumea] were all discovered as my wife was 3-6 months pregnant with our daughter. I have the distinct memory of feeling this fertile abundance pouring out of the entire Universe. Makemake was part of that.
Gonggong was discovered on 17 July 2007 by Megan Schwamb, a graduate student of Mike Brown. It was named after a Chinese water god in an online poll run by the discovery team. The god Gonggong is often depicted as a red-headed human with a snake’s body. He is attended to by a snake-monster named Xiangliu, for whom the planet Gonggong’s moon is named.
Sources:
Duncan, Martin, Thomas Quinn, and Scott Tremaine. “The Origin of Short Period Comets.” The Astrophysical Journal, 328, 15 May 1988, L69, L72. SAO/NASA Astrophysics Data System.
Edgeworth, Kenneth E. “The Evolution of Our Planetary System.” Journal of the British Astronomical Association, 53.6, July 1943, 181–88. SAO/NASA Astrophysics Data System.
International Astronomical Union (IAU). “Fourth Dwarf Planet Named Makemake” (Press Release IAU0806), 19 July 2008.
———. “IAU Names Dwarf Planet Eris” (Press Release IAU0605), 14 September 2006.
———. “IAU Names Fifth Dwarf Planet Haumea.” (Press Release IAU 08070), 17 September 2008.
Kerr, Richard A. “Comet Source: Close to Neptune.” Science, 239, 18 March 1988, 1372/2–1373/1. ProQuest.
Kuiper, Gerard P. “On the Origin of the Solar System.” In J.A. Hynek, ed. Astrophysics: A Topical Symposium. New York: McGraw-Hill, 1951, 357–424 at 400–403. Archive.org.
Minor Planet Center. Minor Planet Circular, 20 November 2002, 47170. (PDF)
———. Minor Planet Circular, 26 November 2004, 53177. (PDF)
———. Minor Planet Circular, 6 November 2016, 73984. (PDF)
———. Minor Planet Circular, 5 February 2020, 121135. (PDF)
Oxford English Dictionary, third edition, September 2007, s.v. Kuiper belt, n.
Image credit: WilyD, 2015. Wikimedia Commons. Licensed under a Creative Commons Attribution-Share Alike 3.0 Unported license.