Kuiper belt

Artist's rendering of the Kuiper Belt and more distant Oort cloud.

The Kuiper belt ("KYE per") is an area of the solar system extending from within the orbit of Neptune (at 30 AU) to 50 AU from the Sun, at inclinations consistent with the ecliptic.

Objects within the Kuiper Belt are referred to by the IAU as trans-Neptunian objects (a type of minor planet). They are sometimes also called asteroids.

The outer boundary of the Kuiper belt is not defined arbitrarily; rather, there appears to be a real and fairly sharp dropoff in objects beyond a certain distance. This is sometimes called the "Kuiper gap" or "Kuiper cliff". The cause for this remains a mystery; one possible explanation would be a hypothetical Earth-sized or Mars-sized object sweeping away debris.

1 Origins
- 1.1 Name
2 Kuiper belt objects
3 External links and data sources

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Origins

Modern computer simulations show the Kuiper belt to have been formed by the work of Jupiter, the young Jupiter having used its considerable gravity to eject smaller bodies which didn't all escape completely, and also having been formed in-situ. The same simulations and other theories predict there should be bodies of significant mass in the belt, Mars-sized or Earth-sized.

The first astronomers to suggest the existence of this belt were Frederick C. Leonard in 1930 and Kenneth E. Edgeworth in 1943. In 1951 Gerard Kuiper suggested that objects did not exist in the belt anymore. More detailed conjectures about objects in the belt were done by Al G. W. Cameron in 1962, Fred L. Whipple in 1964, and Julio Fernandez in 1980. The belt and the objects in it were named after Kuiper after the discovery of (15760) 1992 QB₁.

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Name

An alternative name, Edgeworth-Kuiper belt is used to credit Edgeworth. The term trans-Neptunian object is recommended for objects in the belt by several scientific groups because the term is less controversial than all others — it is not a synonym though, as TNOs include all objects orbiting the Sun at the outer edge of the solar system, not just those in the Kuiper belt.

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Kuiper belt objects

TNOs and similar bodies
Non-trans-Neptunian objects Centaurs Trans-Neptunian objects (TNOs) Kuiper belt objects (KBOs) cubewanos (classical KBOs) plutinos (3:2 resonant KBOs) twotinos (2:1 resonant KBOs) Scattered disc objects (SDOs) Oort cloud objects (OCOs)

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Discoveries thus far

Over 800 Kuiper belt objects (KBOs) (a subset of trans-Neptunian objects (TNOs)) have been discovered in the belt, almost all of them since 1992. Among the largest are Pluto and Charon, but since the year 2000 other large objects that approached their size were identified. 50000 Quaoar, discovered in 2002, which is a KBO, is half the size of Pluto and is larger than the largest asteroid 1 Ceres. 2005 FY₉ and 2003 EL₆₁, both announced on 29 July 2005, are larger still. Other objects, such as 28978 Ixion (discovered in 2001) and 20000 Varuna (discovered in 2000) while smaller than Quaoar, are nonetheless quite sizable. The exact classification of these objects is unclear, since they are probably fairly different from the asteroids of the asteroid belt.

Neptune's moon Triton is commonly thought to be a captured KBO.

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Orbital trajectories

KBOs are by (current) definition limited to 30-44 AU from the Sun. This is not merely an arbitrary definition but reflects a real lack of objects beyond a certain distance. However, most of the known KBOs are detected near their closest approaches to the Sun since they appear dimmer at greater distances.

Some KBOs that also periodically travel inside Neptune's orbit are in 1:2, 2:3 (plutinos), 2:5, 3:4, 3:5, 4:5, or 4:7 orbital resonance with Neptune. Cubewanos, or "classical KBOs" are in more circular nonresonant orbits, which form the core of the belt.

The belt should not be confused with the Oort cloud, which is not limited to the plane of the solar system and is more distant.

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Term "kuiper belt object"

Most models of solar system formation show icy planetoids first forming in the Kuiper belt, and then subsequent gravitational interactions displaced some of them outwards into the so-named scattered disc. While, strictly speaking, a KBO is any object that orbits exclusively within the defined Kuiper belt region regardless of origin or composition, in some scientific circles the term has come to employed as synonymous with any icy planetoid native to the outer solar sytem believed to have been part of that initial class, even if it has orbited beyond the belt for billions of years. Discoverer Michael E. Brown, for instance, has referred to 2003 UB₃₁₃ as a KBO, despite it having an orbital radius of 67 AU, well clear of the Kuiper cliff. Other leading trans-Neptunian researchers have been more cautious in applying the KBO label to objects clearly outside the belt in the current epoch.

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Largest KBOs

The brightest known KBOs (with absolute magnitudes < 4.0), are:

Permanent Designation	Provisional Designation	Absolute magnitude	Albedo	Equatorial diameter (km)	Semimajor axis (AU)	Date discovered	Discoverer	Diameter method
Pluto		−1.0	0.6	2320	39.4	1930	C. Tombaugh	occultation
	2005 FY₉	−0.2	0.6 (assumed)	~1900	45.7	2005	M. Brown, C. Trujillo & D. Rabinowitz	assumed albedo
	2003 EL₆₁	0.1	0.6 (assumed)	~1600	43.3	2005	J.L. Ortiz et al.	assumed albedo
Charon		1	0.4	1205	39.4	1978	J. Christy	occultation
(90482) Orcus	2004 DW	2.3	0.1 (assumed)	~1500	39.4	2004	M. Brown, C. Trujillo & D. Rabinowitz	assumed albedo
(50000) Quaoar	2002 LM₆₀	2.6	0.10 ± 0.03	1260 ± 190	43.5	2002	C. Trujillo & M. Brown	disk resolved
(28978) Ixion	2001 KX₇₆	3.2	0.25 – 0.50	400 – 550	39.6	2001	Deep Ecliptic Survey	thermal
55636	2002 TX₃₀₀	3.3	> 0.19	< 709	43.1	2002	NEAT	thermal
55565	2002 AW₁₉₇	3.3	0.14 – 0.20	650 – 750	47.4	2002	C. Trujillo, M. Brown, E. Helin, S. Pravdo, K. Lawrence & M. Hicks / Palomar Observatory	thermal
55637	2002 UX₂₅	3.6	0.08?	~910	42.5	2002	A. Descour / Spacewatch	assumed albedo
(20000) Varuna	2000 WR₁₀₆	3.7	0.12 – 0.30	450 – 750	43.0	2000	R. McMillan	thermal
	2002 MS₄	3.8	0.1 (assumed)	730?	41.8			assumed albedo
	2003 AZ₈₄	3.9	0.1 (assumed)	700?	39.6			assumed albedo

The list has been sorted by increasing absolute magnitude. Estimated diameter is greatly affected by surface albedo which is often assumed, rather than measured. Some potentially large Kuiper belt objects have not been included.

Sources: [1], [2], [3]

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