Editing Kuiper belt (section)

== History ==
[[File:Pluto-Charon-v2-10-1-15.jpg|thumb|Pluto and Charon]]

After the discovery of Pluto in 1930, many speculated that it might not be alone. The region now called the Kuiper belt was hypothesized in various forms for decades. It was only in 1992 that the first direct evidence for its existence was found. The number and variety of prior speculations on the nature of the Kuiper belt have led to continued uncertainty as to who deserves credit for first proposing it.<ref name=Randall_2015>{{cite book |title=Dark Matter and the Dinosaurs |publisher=Ecco/HarperCollins Publishers |location=New York |first=Lisa |last=Randall |date=2015 |isbn=978-0-06-232847-2 |title-link=Dark Matter and the Dinosaurs}}
</ref>{{rp|page=106}}

=== Hypotheses ===
The first [[astronomer]] to suggest the existence of a trans-Neptunian population was [[Frederick C. Leonard]]. Soon after Pluto's discovery by [[Clyde Tombaugh]] in 1930, Leonard pondered whether it was "likely that in Pluto there has come to light the ''first'' of a ''series'' of ultra-Neptunian bodies, the remaining members of which still await discovery but which are destined eventually to be detected".<ref>{{cite web |title=What is improper about the term "Kuiper belt"? (or, Why name a thing after a man who didn't believe its existence?) |url=http://www.icq.eps.harvard.edu/kb.html |work=International Comet Quarterly |access-date=24 October 2010 |archive-date=8 October 2019 |archive-url=https://web.archive.org/web/20191008115030/http://www.icq.eps.harvard.edu/kb.html |url-status=live }}</ref> That same year, astronomer [[Armin Otto Leuschner|Armin O. Leuschner]] suggested that Pluto "may be one of many long-period planetary objects yet to be discovered."<ref name=lauch>{{cite book |first1=John K. |last1=Davies |first2=J. |last2=McFarland |first3=Mark E. |last3=Bailey |first4=Brian G. |last4=Marsden |first5=W. I. |last5=Ip |title=The Solar System Beyond Neptune |editor=M. Antonietta Baracci |editor2=Hermann Boenhardt |editor3=Dale Cruikchank |editor4=Alessandro Morbidelli |pages=11–23 |publisher=University of Arizona Press |chapter-url=http://www.arm.ac.uk/preprints/2008/522.pdf |date=2008 |chapter=The Early Development of Ideas Concerning the Transneptunian Region |access-date=5 November 2014 |archive-url=https://web.archive.org/web/20150220182134/http://www.arm.ac.uk/preprints/2008/522.pdf |archive-date=20 February 2015 |url-status=dead }}</ref>

[[File:Gerard Kuiper 1964b.jpg|thumb|upright|Astronomer [[Gerard Kuiper]], after whom the Kuiper belt is named]]

In 1943, in the ''[[Journal of the British Astronomical Association]]'', [[Kenneth Edgeworth]] hypothesized that, in the region beyond [[Neptune]], the material within the [[primordial element|primordial]] [[solar nebula]] was too widely spaced to condense into planets, and so rather condensed into a myriad smaller bodies. From this he concluded that "the outer region of the solar system, beyond the orbits of the planets, is occupied by a very large number of comparatively small bodies"<ref name=Davies_2001>{{cite book |title=Beyond Pluto: Exploring the outer limits of the solar system |first=John K. |last=Davies |publisher=Cambridge University Press |date=2001 }}</ref>{{rp|page=xii}} and that, from time to time, one of their number "wanders from its own sphere and appears as an occasional visitor to the inner solar system",<ref name=Davies_2001/>{{rp|page=2}} becoming a [[comet]].

In 1951, in a paper in ''Astrophysics: A Topical Symposium'', [[Gerard Kuiper]] speculated on a similar disc having formed early in the Solar System's evolution and concluded that the disc consisted of "remnants of original clusterings which have lost many members that became stray asteroids, much as has occurred with open galactic clusters dissolving into stars."<ref name = "Kuiper"/> In another paper, based upon a lecture Kuiper gave in 1950, also called ''On the Origin of the Solar System'', Kuiper wrote about the "outermost region of the solar nebula, from 38 to 50 astr. units (i.e., just outside proto-Neptune)" where "condensation products (ices of H20, NH3, CH4, etc.) must have formed, and the flakes must have slowly collected and formed larger aggregates, estimated to range up to 1 km. or more in size." He continued to write that "these condensations appear to account for the comets, in size, number and composition." According to Kuiper "the planet Pluto, which sweeps through the whole zone from 30 to 50 astr. units, is held responsible for having started the scattering of the comets throughout the solar system."<ref>{{cite journal |first1=Gerard |last1=Kuiper |title=On the Origin of the Solar System|journal=Proceedings of the National Academy of Sciences |volume=37 |issue=1 |date=1951 |pages=1–14 |doi=10.1073/pnas.37.4.233 |pmid=16588984 |pmc=1063291 |doi-access= free}}</ref> It is said that Kuiper was operating on the assumption, common in his time, that [[Pluto]] was the size of Earth and had therefore scattered these bodies out toward the [[Oort cloud]] or out of the Solar System; there would not be a Kuiper belt today if this were correct.<ref name="Jewitt">{{cite web |title=WHY "KUIPER" BELT? |author=David Jewitt |work=University of Hawaii |url=http://www2.ess.ucla.edu/~jewitt/kb/gerard.html |access-date=14 June 2007 |archive-date=12 February 2019 |archive-url=https://web.archive.org/web/20190212100219/http://www2.ess.ucla.edu/~jewitt/kb/gerard.html |url-status=live }}</ref>

The hypothesis took many other forms in the following decades. In 1962, physicist [[Alastair GW Cameron|Al G.W. Cameron]] postulated the existence of "a tremendous mass of small material on the outskirts of the solar system".<ref name=Davies_2001/>{{rp|page=14}} In 1964, [[Fred Whipple]], who popularised the famous "[[dirty snowball]]" hypothesis for cometary structure, thought that a "comet belt" might be massive enough to cause the purported discrepancies in the orbit of [[Uranus]] that had sparked the search for [[Planet X]], or, at the very least, massive enough to affect the orbits of known comets.<ref>{{cite journal |journal=Proceedings of the National Academy of Sciences |volume=51 |issue=5 |pages=771–774 |url=http://www.pnas.org/cgi/reprint/51/5/711.pdf |date=1964 |bibcode=1964PNAS...51..771R |doi=10.1073/pnas.51.5.771 |title=Decomposition of Vector Measures |last1=Rao |first1=M. M. |pmid=16591174 |pmc=300359 |doi-access=free |access-date=20 June 2007 |archive-date=3 June 2016 |archive-url=https://web.archive.org/web/20160603080459/http://www.pnas.org/content/51/5/711.full.pdf |url-status=live }}</ref> Observation ruled out this hypothesis.<ref name=Davies_2001/>{{rp|page=14}}

In 1977, [[Charles Kowal]] discovered [[2060 Chiron]], an icy planetoid with an orbit between Saturn and Uranus. He used a [[blink comparator]], the same device that had allowed Clyde Tombaugh to discover Pluto nearly 50 years before.<ref>{{cite journal |title=The discovery and orbit of /2060/ Chiron |author=CT Kowal |author2=W Liller |author3=BG Marsden |place=Hale Observatories, Harvard–Smithsonian Center for Astrophysics |date=1977 |bibcode=1979IAUS...81..245K |volume=81 |page=245 |journal=In: Dynamics of the Solar System; Proceedings of the Symposium}}</ref> In 1992, another object, [[5145 Pholus]], was discovered in a similar orbit.<ref>{{cite journal |title=1992 AD |author=JV Scotti |author2=DL Rabinowitz |author3=CS Shoemaker |author4=EM Shoemaker |author5=DH Levy |author6=TM King |author7=EF Helin |author8=J Alu |author9=K Lawrence|author10=RH McNaught |author11=L Frederick |author12=D Tholen |author13=BEA Mueller |bibcode=1992IAUC.5434....1S |date=1992 |issue=5434 |page=1 |journal=IAU Circ.}}</ref> Today, an entire population of comet-like bodies, called the [[centaur (planetoid)|centaurs]], is known to exist in the region between Jupiter and Neptune. The centaurs' orbits are unstable and have dynamical lifetimes of a few million years.<ref name="Horner2004a">{{cite journal |last1=Horner |first1=J. |last2=Evans |first2=N. W. |last3=Bailey |first3=Mark E. |title=Simulations of the Population of Centaurs I: The Bulk Statistics |date=2004 |volume=354 |pages=798–810 |journal=MNRAS |arxiv=astro-ph/0407400 |bibcode=2004MNRAS.354..798H |doi=10.1111/j.1365-2966.2004.08240.x |issue=3|doi-access=free |s2cid=16002759 }}</ref> From the time of Chiron's discovery in 1977, astronomers have speculated that the centaurs therefore must be frequently replenished by some outer reservoir.<ref name=Davies_2001/>{{rp|page=38}}

Further evidence for the existence of the Kuiper belt later emerged from the study of comets. That comets have finite lifespans has been known for some time. As they approach the Sun, its heat causes their [[volatility (physics)|volatile]] surfaces to sublimate into space, gradually dispersing them. In order for comets to continue to be visible over the age of the Solar System, they must be replenished frequently.<ref name="matter">{{cite journal |author=David Jewitt |title=From Kuiper Belt Object to Cometary Nucleus: The Missing Ultrared Matter |journal=[[The Astronomical Journal]] |volume=123 |issue=2 |pages=1039–1049 |date=2002 |doi=10.1086/338692 |bibcode=2002AJ....123.1039J |s2cid=122240711 |doi-access=free }}</ref> A proposal for such an area of replenishment is the [[Oort cloud]], possibly a spherical swarm of comets extending beyond 50,000&nbsp;AU from the Sun first hypothesised by Dutch astronomer [[Jan Oort]] in 1950.<ref>{{cite journal |bibcode=1950BAN....11...91O |title=The structure of the cloud of comets surrounding the Solar System and a hypothesis concerning its origin |last1=Oort |first1=J. H. |volume=11 |date=1950 |page=91 |journal=Bull. Astron. Inst. Neth.}}</ref> The Oort cloud is thought to be the point of origin of [[long-period comet]]s, which are those, like [[Comet Hale–Bopp|Hale–Bopp]], with orbits lasting thousands of years.<ref name=Randall_2015/>{{rp|page=105}}[[File:Julio A. Fernandez (recortado).jpg|thumb|In 1980, astronomer [[Julio Ángel Fernández|Julio Fernandez]] predicted the existence of a belt. It has been said that because the words "Kuiper" and "comet belt" appeared in the opening sentence of Fernandez's paper, this hypothetical region was referred to as the "Kuiper belt".<ref>{{cite web|access-date=16 August 2020|date=8 October 2019|language=en-US|title=Kuiper Belt {{!}} Facts, Information, History & Definition|url=https://nineplanets.org/kuiper-belt/|website=The Nine Planets|archive-date=16 May 2021|archive-url=https://web.archive.org/web/20210516004242/https://nineplanets.org/kuiper-belt/|url-status=live}}<!-- auto-translated by Module:CS1 translator --></ref>]]There is another comet population, known as [[short-period comet|short-period]] or [[periodic comet]]s, consisting of those comets that, like [[Halley's Comet]], have [[orbital period]]s of less than 200&nbsp;years. By the 1970s, the rate at which short-period comets were being discovered was becoming increasingly inconsistent with their having emerged solely from the Oort cloud.<ref name=Davies_2001/>{{rp|page=39}} For an Oort cloud object to become a short-period comet, it would first have to be [[asteroid capture|captured]] by the giant planets. In a paper published in ''[[Monthly Notices of the Royal Astronomical Society]]'' in 1980, Uruguayan astronomer [[Julio Ángel Fernández|Julio Fernández]] stated that for every short-period comet to be sent into the inner Solar System from the Oort cloud, 600 would have to be ejected into [[Outer space#Interstellar space|interstellar space]]. He speculated that a comet belt from between 35 and 50&nbsp;AU would be required to account for the observed number of comets.<ref>{{cite journal |title=On the existence of a comet belt beyond Neptune |author=J.A. Fernández |bibcode=1980MNRAS.192..481F |date=1980 |volume=192 |issue=3 |pages=481–491 |journal=Monthly Notices of the Royal Astronomical Society |doi=10.1093/mnras/192.3.481 |doi-access=free}}</ref> Following up on Fernández's work, in 1988 the Canadian team of Martin Duncan, Tom Quinn and [[Scott Tremaine]] ran a number of computer simulations to determine if all observed comets could have arrived from the Oort cloud. They found that the Oort cloud could not account for all short-period comets, particularly as short-period comets are clustered near the plane of the Solar System, whereas Oort-cloud comets tend to arrive from any point in the sky. With a "belt", as Fernández described it, added to the formulations, the simulations matched observations.<ref>{{cite journal |title=The origin of short-period comets |author=M. Duncan |author2=T. Quinn |author3=S. Tremaine |name-list-style=amp |date=1988 |bibcode=1988ApJ...328L..69D |volume=328 |pages=L69 |journal=Astrophysical Journal |doi=10.1086/185162|doi-access=free }}</ref> Reportedly because the words "Kuiper" and "comet belt" appeared in the opening sentence of Fernández's paper, Tremaine named this hypothetical region the "Kuiper belt".<ref name=Davies_2001/>{{rp|page=191}}

=== Discovery ===
[[File:Mauna Kea Summit 2021-06-16 33 (cropped).jpg|thumb|upright=1.25|Telescopes atop [[Mauna Kea Observatories|Mauna Kea]]. The Kuiper belt was discovered with [[UH88]], which is the fourth from the left.]]
In 1987, astronomer [[David Jewitt]], then at [[MIT]], became increasingly puzzled by "the apparent emptiness of the outer Solar System".<ref name="qbee">{{cite journal |doi=10.1038/362730a0 |title=Discovery of the candidate Kuiper belt object 1992 QB1 |date=1993 |last1=Jewitt |first1=David |last2=Luu |first2=Jane |journal=Nature |volume=362 |issue=6422 |pages=730–732 |bibcode=1993Natur.362..730J|s2cid=4359389 }}</ref> He encouraged then-graduate student [[Jane Luu]] to aid him in his endeavour to locate another object beyond [[Pluto]]'s orbit, because, as he told her, "If we don't, nobody will."<ref name=Davies_2001/>{{rp|page=50}} Using telescopes at the [[Kitt Peak National Observatory]] in Arizona and the [[Cerro Tololo Inter-American Observatory]] in Chile, Jewitt and Luu conducted their search in much the same way as Clyde Tombaugh and Charles Kowal had, with a [[blink comparator]].<ref name=Davies_2001/>{{rp|page=50}} Initially, examination of each pair of plates took about eight hours,<ref name=Davies_2001/>{{rp|page=51}} but the process was sped up with the arrival of electronic [[charge-coupled device]]s or CCDs, which, though their field of view was narrower, were not only more efficient at collecting light (they retained 90% of the light that hit them, rather than the 10% achieved by photographs) but allowed the blinking process to be done virtually, on a computer screen. Today, CCDs form the basis for most astronomical detectors.<ref name=Davies_2001/>{{rp|pages=52, 54, 56}} In 1988, Jewitt moved to the Institute of Astronomy at the [[University of Hawaii]]. Luu later joined him to work at the University of Hawaii's 2.24&nbsp;m telescope at [[Mauna Kea]].<ref name=Davies_2001/>{{rp|pages=57, 62}} Eventually, the field of view for CCDs had increased to 1024 by 1024 pixels, which allowed searches to be conducted far more rapidly.<ref name=Davies_2001/>{{rp|page=65}} Finally, after five years of searching, Jewitt and Luu announced on 30 August 1992 the "Discovery of the candidate Kuiper belt object [[15760 Albion|1992 QB<sub>1</sub>]]".<ref name=qbee/> This object would later be named 15760 Albion. Six months later, they discovered a second object in the region, [[(181708) 1993 FW]].<ref>{{cite journal |title=1993 FW |author1=Marsden, B.S. |place=Minor Planet Center |bibcode=1993IAUC.5730....1L |date=1993 |author2=Jewitt, D. |author3=Marsden, B.G. |issue=5730 |page=1 |journal=IAU Circ.}}</ref> By 2018, over 2000&nbsp;Kuiper belts objects had been discovered.<ref name="Dyches">{{Cite web |url=https://solarsystem.nasa.gov/news/792/10-things-to-know-about-the-kuiper-belt |title=10&nbsp;Things to Know About the Kuiper Belt |last=Dyches |first=Preston |website=NASA Solar System Exploration |date=14 December 2018 |access-date=2019-12-01 |archive-date=10 January 2019 |archive-url=https://web.archive.org/web/20190110003110/https://solarsystem.nasa.gov/news/792/10-things-to-know-about-the-kuiper-belt |url-status=live }}</ref>

Over one thousand bodies were found in a belt in the twenty years (1992–2012), after finding {{mp|1992 QB|1}} (named in 2018, 15760 Albion), showing a vast belt of bodies in addition to Pluto and Albion.<ref name=":2">{{cite web |url=https://www.astrobio.net/also-in-news/the-kuiper-belt-at-20/ |title=The Kuiper Belt at 20 |date=2012-09-01 |website=Astrobiology Magazine |access-date=2019-12-01 |archive-url=https://web.archive.org/web/20201030081029/https://www.astrobio.net/also-in-news/the-kuiper-belt-at-20/ |archive-date=2020-10-30 |url-status=dead}}</ref> Even in the 2010s the full extent and nature of Kuiper belt bodies was largely unknown.<ref name=":2"/> Finally, the unmanned spacecraft [[New Horizons]] conducted the first KBO flybys, providing much closer observations of the Plutonian system (2015) and then [[Arrokoth]] (2019).<ref>{{cite web |url=https://www.science.org/content/article/surviving-encounter-beyond-pluto-nasa-probe-begins-relaying-view-kuiper-belt-object |title=Surviving encounter beyond Pluto, NASA probe begins relaying view of Kuiper belt object |last=Voosen |first=Paul |date=2019-01-01 |website=Science |publisher=AAAS |access-date=2019-12-01 |archive-date=8 October 2022 |archive-url=https://web.archive.org/web/20221008185849/https://www.science.org/content/article/surviving-encounter-beyond-pluto-nasa-probe-begins-relaying-view-kuiper-belt-object |url-status=live }}</ref>

Studies conducted since the trans-Neptunian region was first charted have shown that the region now called the Kuiper belt is not the point of origin of short-period comets, but that they instead derive from a linked population called the [[scattered disc]]. The scattered disc was created when Neptune [[Nice model|migrated outward]] into the proto-Kuiper belt, which at the time was much closer to the Sun, and left in its wake a population of dynamically stable objects that could never be affected by its orbit (the Kuiper belt proper), and a population whose [[apsis|perihelia]] are close enough that Neptune can still disturb them as it travels around the Sun (the scattered disc). Because the scattered disc is dynamically active and the Kuiper belt relatively dynamically stable, the scattered disc is now seen as the most likely point of origin for periodic comets.<ref name=book/>

=== Name ===
Astronomers sometimes use the alternative name Edgeworth–Kuiper belt to credit Edgeworth, and KBOs are occasionally referred to as EKOs. [[Brian G. Marsden]] claims that neither deserves true credit: "Neither Edgeworth nor Kuiper wrote about anything remotely like what we are now seeing, but [[Fred Whipple]] did".<ref name=Davies_2001/>{{rp|page=199}} David Jewitt comments: "If anything ... [[Julio Ángel Fernández|Fernández]] most nearly deserves the credit for predicting the Kuiper Belt."<ref name=Jewitt />

KBOs are sometimes called "kuiperoids", a name suggested by [[Clyde Tombaugh]].<ref>Clyde Tombaugh, "The Last Word", Letters to the Editor, ''Sky & Telescope'', December 1994, p. 8</ref> The term "[[trans-Neptunian object]]" (TNO) is recommended for objects in the belt by several scientific groups because the term is less controversial than all others—it is not an exact [[synonym]], though, as TNOs include all objects orbiting the Sun past the orbit of [[Neptune]], not just those in the Kuiper belt.<ref>{{cite web|url=http://www.icq.eps.harvard.edu/kb.html|title=What is improper about the term "Kuiper belt"?|website=International Comet Quarterly|access-date=19 December 2021|archive-date=8 October 2019|archive-url=https://web.archive.org/web/20191008115030/http://www.icq.eps.harvard.edu/kb.html|url-status=live}}</ref>