View source for Scattered disk radiation astronomy

'''Editor-In-Chief:''' Henry A. Hoff
[[Image:TheKuiperBelt 100AU SDO.svg|thumb|center|400px|The diagram shows scattered disc objects out to 100 AU. Credit: [[commons:User:Eurocommuter|Eurocommuter]].]]
Scattered Disk Objects (up to 100 AU): Kuiper Belt objects are shown in grey, resonant objects within the Scattered Disk are shown in green. 

The position of an object represents 
* its orbit’s semi-major axis '''a''' in AU and the orbital period in years (horizontal axis)
* its orbit’s inclination '''i''' in degrees (vertical axis).

The size of the circle illustrates the object’s size relative to others. For a few large objects, the diameter drawn represents the best current estimates. For all others, the circles represent the absolute magnitude of the object. 

The eccentricity of the orbit is shown indirectly by a segment extending from the left (perihelion) to the aphelion to the right. In other words, the segment illustrates the variations of the object's distance from the Sun. Objects with nearly circular orbits will show short segments while highly elliptical orbits will be represented by long segments. 

Main resonances with Neptune are marked with vertical bars; 1:1 marks the position of Neptune’s orbit (and its Trojan asteroids), 2:3 marks the orbit of [[Draft:Pluto|Pluto]] (and plutinos) etc.

The scattered disc (or scattered disk) is a distant region of the [[Solar System]] that is sparsely populated by icy minor planets, a subset of the broader family of trans-Neptunian objects. The scattered-disc objects (SDOs) have orbital eccentricities ranging as high as 0.8, inclinations as high as 40°, and perihelia greater than 30 astronomical units (4.5 x 10<sup>9</sup> km; 2.8 x 10<sup>9</sup> mi.). While the nearest distance to the Sun approached by scattered objects is about 30–35&nbsp;AU, their orbits can extend well beyond 100&nbsp;AU. This makes scattered objects "among the most distant and cold objects in the Solar System".<ref name=Masetti>Maggie Masetti. (2007). ''[http://heasarc.gsfc.nasa.gov/docs/cosmic/solar_system_info.html Cosmic Distance Scales&nbsp;– The Solar System]''. Website of NASA's High Energy Astrophysics Science Archive Research Center. Retrieved 2008 07-12.</ref>

The innermost portion of the scattered disc overlaps with a torus-shaped region of orbiting objects traditionally called the Kuiper belt,<ref name="Morbidelli2008" /> but its outer limits reach much farther away from the Sun and farther above and below the ecliptic than the Kuiper belt proper. The literature is inconsistent in the use of the phrases "scattered disc" and "Kuiper belt"; for some, they are distinct populations; for others, the scattered disc is part of the Kuiper belt and authors may even switch between these two uses in a single publication.<ref>McFadden, Weissman, & Johnson (2007). ''Encyclopedia of the Solar System'', footnote p. 584</ref>
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==Periodic comets==
[[Image:Rosetta OSIRIS NAC comet 67P 20140803 2 625.jpg|thumb|right|250px|This image shows Comet 67P/Churyumov-Gerasimenko. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/ UPM/DASP/IDA.]]
[[Image:Rosetta OSIRIS NAC comet 67P 20140803 1 625.jpg|thumb|left|250px|This image shows Comet 67P/Churyumov-Gerasimenko rotated around a vertical axis from the right. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/ UPM/DASP/IDA.]]
[[Image:Comet 67P-C-G.jpg|thumb|right|250px|This is an image of the nucleus of Comet 67P/Churyumov-Gerasimenko by Rosetta. Credit: ESA Rosetta Mission.{{tlx|free media}}]]
[[Image:Comet 67P C-G on 6 Mar 2015 NavCam.jpg|left|thumb|250px|Single frame Rosetta spacecrast NAVCAM image of Comet 67P/C-G was taken on 6 March from a distance of 82.9 km to the comet. Credit: ESA/Rosetta/NAVCAM.{{tlx|free media}}]]
[[Image:Comet 67P on 19 September 2014 NavCam mosaic.jpg|right|thumb|250px|Images taken by the ''Rosetta'' navigation camera (NAVCAM) on 19 September 2014 at 28.6 km (17.8 mi) from the centre of comet 67P/Churyumov–Gerasimenko. Credit: ESA/Rosetta/NAVCAM.{{tlx|free media}}]]
[[Image:Comet 67P on 24 October - NAVCAM (15464989957).jpg|left|thumb|250px|Four-image montage comprises images taken by Rosetta's navigation camera from a distance of 9.8 km from the centre of comet 67P/C-G – about 7.8 km from the surface. Credit: ESA/Rosetta/NAVCAM.{{tlx|free media}}]]
[[Image:Comet 67P on 26 October - NAVCAM (15038644724).jpg|right|thumb|250px|Image is taken by Rosetta's navigation camera from a distance of 9.8 km from the centre of comet 67P/C-G Credit: ESA/Rosetta/NAVCAM.{{tlx|free media}}]]
The image at the right is an optical astronomy image of the comet 67P/Churyumov-Gerasimenko. Rosetta's OSIRIS narrow-angle camera made the image on 3 August 2014 from a distance of 285 km. The image resolution is 5.3 metres/pixel.

The left image is rotated 90° from the right. The location of the right image is the front view of the left side just out of view in the left image. The object rotates by the right hand rule from the left image to the right.

Note that due to the evaporation of volatiles, the surface of the rocky object appears pitted or cratered.

'''Def.''' a "comet which orbits the Sun and which returns to the innermost point of its orbit at known, regular intervals"<ref name=PeriodicCometWikt>{{ cite web
|author=[[wikt:user:WikiPedant|WikiPedant]]
|title=periodic comet
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=4 November 2007
|url=https://en.wiktionary.org/wiki/periodic_comet
|accessdate=14 June 2019 }}</ref> is called a '''periodic comet'''.
"The short period comets have orbital periods <20 years and low inclination. Their orbits are controlled by Jupiter and thus they are also called Jupiter Family comets. [...]  Because the orbit crosses that of Jupiter, the comet will have gravitational interactions with this massive planet. The objects orbit will gradually change from these interactions and eventually the object will either be thrown out of the Solar System or collide with a planet or the Sun."<ref name=sheppard>{{ cite book
|author=jf
|title=The Jupiter Family Comets
|publisher=Carnegie Institution of Washington
|location=5241 Broad Branch Road, NW, Washington, DC 20015-1305
|date=
|editor=
|pages=1
|url=http://home.dtm.ciw.edu/users/sheppard/satellites/jf.html
|arxiv=
|bibcode=
|doi=
|pmid=
|isbn=
|accessdate=5 February 2018 }}</ref>

Perihleion distance in AU = 1.243, eccentricity = 0.641, inclination = 7.0, and orbital period in years = 2.745.<ref name=fernandez>{{ cite book
|author=yfernandez
|title=List of Jupiter-Family and Halley-Family Comets
|publisher=University of Central Florida
|location=UCF Department of Physics, 4111 Libra Drive Physical Sciences Bldg. 430, Orlando, FL 32816-2385
|date=28 July 2015
|editor=
|pages=1
|url=https://physics.ucf.edu/~yfernandez/cometlist.html#jf
|arxiv=
|bibcode=
|doi=
|pmid=
|isbn=
|accessdate=5 February 2018 }}</ref>

Because of its unstable nature, astronomers now consider the scattered disc to be the place of origin for most periodic comets in the Solar System, with the centaurs, a population of icy bodies between Jupiter and Neptune, being the intermediate stage in an object's migration from the disc to the inner Solar System.<ref name="Horner2004a">{{cite journal |last=Horner |first= J. |author2=Evans, N. W.|author3=Bailey, Mark E. |title=Simulations of the Population of Centaurs I: The Bulk Statistics |date=2004 |arxiv=astro-ph/0407400 |bibcode=2004MNRAS.354..798H |volume=354 |pages=798 |journal=Monthly Notices of the Royal Astronomical Society |doi=10.1111/j.1365-2966.2004.08240.x |issue=3 }}</ref>
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==Centaurs==
{{main|Rocks/Rocky objects/Centaurs|Centaurs}}
[[Image:Kuiper belt plot objects of outer solar system.png|right|330px|thumb|Positions of known outer Solar System objects.<br />The centaurs lie generally inwards of the Kuiper belt and outside the Jupiter trojans.
{| style="width: 100%; margin-bottom: 8px;"
|-
| valign=top width=45% |
{{legend2|#FFFF00|border=1px solid #B3B300|Sun}}<br />
{{legend2|#aaa|border=1px solid #777|Jupiter trojans}}&nbsp;{{small|(6,178)}}<br />
{{legend2|#FFC170|border=1px solid #D67900|Scattered disc}}&nbsp;{{small|(&gt;300)}}
{{legend2|#A300A3|border=1px solid #3D003D|Neptune trojans&nbsp;{{small|(9)}}}}
| valign=top |
{{legend2|#FF4D4D|border=1px solid #FF0000|Giant planets: J{{·}}S{{·}}U{{·}}N}}<br />
{{legend2|#009900|border=1px solid #003300|'''Centaurs'''}}&nbsp;{{small|(44,000)}}<br />
{{legend2|#66CCFF|border=1px solid #00AAFF|Kuiper belt}}&nbsp;{{small|(&gt;100,000)}}
|} Credit: [[w:user:WilyD|WilyD]].]]
[[Image:TheKuiperBelt Albedo and Color.svg|left|thumb|250px|Colour distribution of centaurs is shown. Credit: [[c:user:Eurocommuter~commonswiki|Eurocommuter~commonswiki]].]]
'''Def.''' an "icy planetoid that orbits the Sun between [[Jupiter]] and [[Neptune]]"<ref name=CentaurWikt>{{ cite web
|author=[[wikt:User:SnoopY|SnoopY]]
|title=Centaur
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=21 December 2005
|url=https://en.wiktionary.org/wiki/Centaur
|accessdate=31 August 2015 }}</ref> is called a '''Centaur'''.

"The recent investigation of the orbital distribution of Centaurs (Emel’yanenko et al., 2005) showed that there are two dynamically distinct classes of Centaurs, a dominant group with semimajor axes a > 60 AU and a minority group with a < 60 AU."<ref name=Emelyanenko>{{ cite journal
|author=V. V. Emel’yanenko
|title=Structure and dynamics of the Centaur population: constraints on the origin of short-period comets
|journal=Earth, Moon, and Planets
|month=December
|year=2005
|volume=97
|issue=3-4
|pages=341-51
|url=http://dccm.susu.ac.ru/acm2005.pdf
|bibcode=
|doi=10.1007/s11038-006-9095-5
|pmid=
|accessdate=2011-10-06 }}</ref> "[T]he intrinsic number of such objects is roughly an order of magnitude greater than that for a<60 AU".<ref name=Emelyanenko/>

Centaurs are small Solar System bodies with a semi-major axis between those of the outer planets, generally have unstable orbits because they cross or have crossed the orbits of one or more of the giant planets; almost all their orbits have dynamic lifetimes of only a few million years.<ref name=Horner2004a/> There is one centaur, 514107 Kaʻepaokaʻawela, which may be in a stable (though retrograde) orbit.<ref>{{cite journal |last1=Fathi Namouni and Maria Helena Moreira Morais |title=An interstellar origin for Jupiter's retrograde co-orbital asteroid |journal=Monthly Notices of the Royal Astronomical Society |volume=477 |issue=1 |pages=L117–L121 |date=May 2, 2018 |doi=10.1093/mnrasl/sly057 |url=https://academic.oup.com/mnrasl/article/477/1/L117/4996014|arxiv=1805.09013 |bibcode=2018MNRAS.477L.117N }} For criticism of this idea see {{Cite web  |last       = Billings  |first      = Lee  |date       = 21 May 2018  |title      = Astronomers Spot Potential "Interstellar" Asteroid Orbiting Backward around the Sun  |publisher  = Scientific American  |url        = https://www.scientificamerican.com/article/astronomers-spot-potential-interstellar-asteroid-orbiting-backward-around-the-sun/  |accessdate = 1 June 2018}}</ref> Centaurs typically behave with characteristics of both asteroids and comets and are named after the mythological centaurs that were a mixture of horse and human. It has been estimated that there are around 44,000&nbsp;centaurs in the Solar System with diameters larger than 1 kilometer.<ref name=Horner2004a/>

No centaur has been photographed up close, although there is evidence that [[Saturn]]'s moon Phoebe, imaged by the Cassini–Huygens (''Cassini'') probe in 2004, may be a captured centaur that originated in the Kuiper belt.<ref name="Jewitt2007">{{cite journal|last=Jewitt|first=David|author2=Haghighipour, Nader|title=Irregular Satellites of the Planets: Products of Capture in the Early Solar System|journal=Annual Review of Astronomy and Astrophysics|date=2007|volume=45|issue=1|pages=261–95|url=http://www.ifa.hawaii.edu/~jewitt/papers/2007/JH07.pdf|archiveurl=https://www.webcitation.org/5nMMZRRKe?url=http://www.ifa.hawaii.edu/~jewitt/papers/2007/JH07.pdf|archivedate=2010-02-07|doi=10.1146/annurev.astro.44.051905.092459|bibcode=2007ARA&A..45..261J|arxiv=astro-ph/0703059|deadurl=yes|df=}}</ref>

Even centaurs such as 2000 GM<sub>137</sub> and 2001 XZ<sub>255</sub>}, which do not currently cross the orbit of any planet, are in gradually changing orbits that will be perturbed until they start to cross the orbit of one or more of the giant planets.<ref name=Horner2004a/>

The Minor Planet Center (MPC) defines centaurs as having a perihelion beyond the orbit of Jupiter (''q''&nbsp;>&nbsp;5.2&nbsp;AU) and a semi-major axis less than that of Neptune (''a''&nbsp;<&nbsp;30.1&nbsp;AU).<ref name="MPC-centaur-def">
  {{cite web
  |url=http://www.minorplanetcenter.org/iau/lists/Unusual.html
  |title=Unusual Minor Planets
  |publisher=Minor Planet Center
  |accessdate=2010-10-25}}</ref>

The Jet Propulsion Laboratory (JPL) similarly defines centaurs as having a semi-major axis, ''a'', between those of Jupiter (5.5&nbsp;AU&nbsp;<&nbsp;''a'') and Neptune (''a''&nbsp;<&nbsp;30.1&nbsp;AU).<ref name=jplcent>{{cite web
  |title=Orbit Classification (Centaur)
  |publisher=JPL Solar System Dynamics
  |url=http://ssd.jpl.nasa.gov/sbdb_help.cgi?class=CEN
  |accessdate=2008-10-13}}</ref>

The Deep Ecliptic Survey (DES) defines centaurs using a dynamical classification scheme. These classifications are based on the simulated change in behavior of the present orbit when extended over 10&nbsp;million years. The DES defines centaurs as non-resonant objects whose instantaneous (osculating) perihelia are less than the osculating semi-major axis of Neptune at any time during the simulation. This definition is intended to be synonymous with planet-crossing orbits and to suggest comparatively short lifetimes in the current orbit.<ref name=Elliot2005>{{cite journal
  |last=Elliot |first= J.L.
 |author2=Kern, S. D. |author3=Clancy, K. B. |author4=Gulbis, A. A. S. |author5=Millis, R. L. |author6=Buie, M. W. |author7=Wasserman, L. H. |author8=Chiang, E. I. |author9=Jordan, A. B. |author10=Trilling, D. E. |author11=Meech, K. J.
  |title=The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population
  |journal=The Astronomical Journal
  |volume=129
  |issue=2 |pages=1117–1162 |year=2005
  |doi=10.1086/427395
  |url=http://www.iop.org/EJ/abstract/1538-3881/129/2/1117
  |accessdate=2008-09-22 |bibcode=2005AJ....129.1117E}}</ref>

The collection ''The Solar System Beyond Neptune'' (2008) defines objects with a semi-major axis between those of Jupiter and Neptune and a Jupiter &ndash; Tisserand's parameter above 3.05 &ndash; as centaurs, classifying the objects with a Jupiter Tisserand's parameter below this and, to exclude Kuiper belt objects, an arbitrary perihelion cut-off half-way to Saturn (''q''&nbsp;<&nbsp;7.35 AU) as Jupiter-family comets (This would make 60558 Echeclus (''q''&nbsp;=&nbsp;5.8&nbsp;AU, ''T''<sub>J</sub>&nbsp;=&nbsp;3.03) and 52872 Okyrhoe (''q''&nbsp;=&nbsp;5.8&nbsp;AU; ''T''<sub>J</sub>&nbsp;=&nbsp;2.95), which have traditionally been classified as centaurs, and 944 Hidalgo (''q''&nbsp;=&nbsp;1.95&nbsp;AU; ''T''<sub>J</sub>&nbsp;=&nbsp;2.07), which has traditionally been considered an asteroid and is classified as a centaur by JPL, Jupiter-family comets, not centaurs.) and classifying those objects on unstable orbits with a semi-major axis larger than Neptune's as members of the scattered disc.<ref name="ArizonaBook_Gladman2007">
  {{cite journal
  |title=Nomenclature in the Outer Solar System
  |journal=The Solar System Beyond Neptune|isbn= 978-0-8165-2755-7
  |year=2008
  |first1= B. |last1=Gladman|first2 = B. |last2= Marsden|first3=C. |last3=Van Laerhoven
  |url=http://www.lpi.usra.edu/books/ssbn2008/7002.pdf
  }}
</ref>

Centaurs are objects that are non-resonant with a perihelion inside the orbit of Neptune that can be shown to likely cross the Hill sphere of a gas giant within the next 10&nbsp;million years,<ref name="Chiang2007">{{cite journal
  |last=Chaing |first= Eugene
  |last2=Lithwick| first2=Y. |last3=Murray-Clay| first3=R. |last4=Buie| first4= M. |last5=Grundy| first5=W. |last6=Holman| first6= M.
  |title=A Brief History of Transneptunian Space
  |journal=Protostars and Planets V
  |editor-first1= B. |editor-last1=Reipurth |editor-first2=D. |editor-last2=Jewitt |editor-first3=K. |editor-last3=Keil
  |publisher=University of Arizona Press, Tucson
  |pages=895–911 |year=2007
  |bibcode=2007prpl.conf..895C |arxiv = astro-ph/0601654 }}</ref> so that centaurs can be thought of as objects scattered inwards and that interact more strongly and scatter more quickly than typical scattered-disc objects.

The JPL Small-Body Database lists 452&nbsp;centaurs.<ref name="jplcentaurlist">{{cite web
  |title=JPL Small-Body Database Search Engine: List of centaurs
  |publisher=JPL Solar System Dynamics
|url=http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=all;obj_numbered=all;ast_orbit_class=CEN;OBJ_field=0;ORB_field=0;table_format=HTML;max_rows=100;format_option=comp;c_fields=AcBhBgBjBiBnBsCkCqAi;.cgifields=format_option;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=ast_orbit_class;.cgifields=table_format;.cgifields=com_orbit_class&query=1&c_sort=AiA
  |accessdate=2018-10-11}}</ref> There are an additional 116&nbsp;trans-Neptunian objects (objects with a semi-major axis further than Neptune's, i.e. ''a''&nbsp;>&nbsp;30.1&nbsp;AU) with a perihelion closer than the orbit of Uranus (''q''&nbsp;<&nbsp;19.2&nbsp;AU).<ref name="jplqUranusTNOlist">{{cite web
  |title=JPL Small-Body Database Search Engine: List of TNOs with perihelia closer than Uranus's orbit
  |publisher=JPL Solar System Dynamics
|url=http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=ast;obj_numbered=all;OBJ_field=0;ORB_field=0;combine_mode=AND;c1_group=ORB;c1_item=Bi;c1_op=%3C;c1_value=19;c2_group=ORB;c2_item=Bh;c2_op=%3E;c2_value=30.1;table_format=HTML;max_rows=200;format_option=comp;c_fields=AcBhBgBjBkBlBiBnBsCjCpCmCnCoAi;.cgifields=format_option;.cgifields=ast_orbit_class;.cgifields=combine_mode;.cgifields=table_format;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=com_orbit_class&query=1&c_sort=AiA
  |accessdate=2018-10-11}}</ref>

The Committee on Small Body Nomenclature of the International Astronomical Union has adopted the following naming convention for such objects: Befitting their centaur-like transitional orbits between TNOs and comets, "objects on unstable, non-resonant, giant-planet-crossing orbits with semimajor axes greater than Neptune's" are to be named for other hybrid and shape-shifting mythical creatures. Thus far, only the binary objects 65489 Ceto and Phorcys and 42355 Typhon and Echidna have been named according to the new policy.<ref name="Grundy2007">{{cite journal
  |last1=Grundy |first1= Will
  |first2=J.A.|last2=Stansberry
  |first3=K|last3=Noll
  |first4=D.C.|last4=Stephens
  |first5=D.E.|last5=Trilling|first6=S.D.|last6=Kern|first7=J.R.|last7=Spencer
  |first8=D.P.|last8=Cruikshank|first9=H.F.|last9=Levison
  |title=The orbit, mass, size, albedo, and density of (65489) Ceto/Phorcys: A tidally-evolved binary Centaur
  |journal=Icarus|volume=191|issue=1|pages=286–297 |year=2007
  |arxiv=0704.1523 | doi=10.1016/j.icarus.2007.04.004 |bibcode=2007Icar..191..286G
  }}</ref>

Centaurs with measured diameters listed as possible dwarf planets include 10199 Chariklo, (523727) 2014 NW<sub>65</sub>, 2060 Chiron, and 54598 Bienor.<ref name="Brown-dplist">{{cite web
  |title=How many dwarf planets are there in the outer solar system? (updates daily)
  |publisher=California Institute of Technology
  |last= Brown| first= Michael E.
  |url=http://web.gps.caltech.edu/~mbrown/dps.html
  |accessdate=18 November 2016}}</ref>

The colours of centaurs are very diverse, which challenges any simple model of surface composition.<ref name="Barucci">{{cite web| first1= M. A.| last1= Barucci| first2= A.| last2= Doressoundiram| first3= D. P.| last3= Cruikshank| title= Physical Characteristics of TNOs and Centaurs| year= 2003| url= http://www.lesia.obspm.fr/~alaind/TNO/Barucci2003_comet2.pdf| publisher= Laboratory for Space Studies and Astrophysics Instrumentation, Paris Observatory| accessdate= 20 March 2008| deadurl= yes| archiveurl= https://web.archive.org/web/20080529193555/http://www.lesia.obspm.fr/~alaind/TNO/Barucci2003_comet2.pdf| archivedate= 29 May 2008| df= }}</ref> In the side-diagram, the colour indices are measures of apparent magnitude of an object through blue&nbsp;(B), visible&nbsp;(V) (i.e. green-yellow) and red&nbsp;(R) filters. The diagram illustrates these differences (in exaggerated colours) for all centaurs with known colour indices. For reference, two moons: Triton and Phoebe, and planet Mars are plotted (yellow labels, size not to scale).

Centaurs appear to be grouped into two classes:
* very red &ndash; for example 5145 Pholus
* blue (or blue-grey, according to some authors) &ndash; for example 2060 Chiron

{| class="wikitable"
! Name !! Year !! Discoverer !! Half-life<ref name=Horner2004a/><br />(forward) !! Class
|-
| 55576 Amycus || 2002 || Near Earth Asteroid Tracking (NEAT) at Palomar Observatory || 11.1&nbsp;Ma || UK
|-
| 54598 Bienor || 2000 || Marc W. Buie et al. || ? || U
|-
| 10370 Hylonome || 1995 || Mauna Kea Observatory || 6.3&nbsp;Ma || UN
|-
| 10199 Chariklo || 1997 || Spacewatch || 10.3&nbsp;Ma || U
|-
| 8405 Asbolus || 1995 || Spacewatch (James V. Scotti) || 0.86&nbsp;Ma || SN
|-
| 7066 Nessus || 1993 || Spacewatch (David L. Rabinowitz) || 4.9&nbsp;Ma || SK
|-
| 5145 Pholus || 1992 || Spacewatch (David L. Rabinowitz) || 1.28&nbsp;Ma || SN
|-
| 2060 Chiron || 1977 || Charles T. Kowal || 1.03&nbsp;Ma || SU
|}
{{clear}}

==Trans-Neptunian objects==
[[Image:KBOs and resonances.png|right|thumb|660px|Distribution of trans-Neptunian objects, with semi-major axis on the horizontal, and inclination on the vertical axis. Scattered disc objects are shown in grey, objects that are in resonance with Neptune in red. Classical Kuiper belt objects (cubewanos) and sednoids are blue and yellow, respectively.]]
[[Image:EightTNOs.png|right|thumb|300px|Comparison is of the largest TNOs: Pluto, Eris, Haumea, Makemake, 2007 OR<sub>10</sub>, Quaoar, Sedna, 2002 MS<sub>4</sub>, Orcus and Salacia. All except two of these TNOs (Sedna and 2002 MS<sub>4</sub>) are known to have moon(s). The top 4 are IAU-accepted dwarf planets while the bottom 6 are dwarf-planet candidates that are accepted as dwarf planets by several astronomers. Credit: [[c:user:Lexicon|Lexicon]].{{tlx|free media}}]]
Over a thousand trans-Neptunian objects were detected between 1992 and 2006.<ref>{{cite conference | first=Scott S. | last=Sheppard | title=Small Bodies in the Outer Solar System | booktitle=New Horizons in Astronomy: Frank N. Bash Symposium 2005 | publisher=Astronomical Society of the Pacific | pages=3–14 | date=October 16–18, 2005 | location=Austin, Texas | url=http://www.ciw.edu/sheppard/pub/Sheppard06smallbodies.pdf | accessdate=2008-08-14 | isbn=1-58381-220-2 | deadurl=yes | archiveurl=http://webarchive.loc.gov/all/20061012062457/http://www.ciw.edu/sheppard/pub/Sheppard06smallbodies.pdf | archivedate=2006-10-12 | df= }}</ref>

As of October 2018, the catalog of minor planets contains 528 numbered and more than 2,000 unnumbered TNOs.<ref name="MPC-List-TNOs">{{cite web
  |title      = List Of Transneptunian Objects
  |work       = Minor Planet Center
  |url        = https://minorplanetcenter.net/iau/lists/TNOs.html
  |accessdate = 23 October 2018}}</ref>
<ref name="MPC-List-Cen-and-SDO">{{cite web
  |title      = List Of Centaurs and Scattered-Disk Objects
  |work       = Minor Planet Center
  |date       = 8 October 2018
  |url        = https://minorplanetcenter.net/iau/lists/Centaurs.html
  |accessdate = 23 October 2018}}</ref>
<ref name="TNO-list-Johnstons">{{cite web
  |title      = List of Known Trans-Neptunian Objects
  |work       = Johnston's Archive
  |date       = 7 October 2018
  |url        = http://www.johnstonsarchive.net/astro/tnoslist.html
  |accessdate = 23 October 2018}}</ref><ref name="JPL-TNO-query-I">{{cite web
  |title=JPL Small-Body Database Search Engine: orbital class (TNO)
  |publisher=JPL Solar System Dynamics
  |url=http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=all;obj_numbered=all;ast_orbit_class=TNO;OBJ_field=0;ORB_field=0;table_format=HTML;max_rows=100;format_option=comp;c_fields=AcBhBgBjBiBnBsCjCpAi;.cgifields=format_option;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=ast_orbit_class;.cgifields=table_format;.cgifields=com_orbit_class&query=1&c_sort=AiA
  |accessdate=2014-07-10}}</ref><ref name="JPL-TNO-query-II">{{cite web
  |title=JPL Small-Body Database Search Engine: orbital class (TNO) and q > 30.1 (AU)
|url=http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=all;obj_numbered=all;ast_orbit_class=TNO;OBJ_field=0;ORB_field=0;c1_group=ORB;c1_item=Bi;c1_op=%3E;c1_value=30.1;table_format=HTML;max_rows=100;format_option=comp;c_fields=AcBhBgBjBiBnBsCjCpAi;.cgifields=format_option;.cgifields=obj_kind;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=ast_orbit_class;.cgifields=table_format;.cgifields=com_orbit_class&query=1&c_sort=AiA
  |accessdate=2014-07-11}}</ref>

Twelve minor planets with a semi-major axis greater than 150&nbsp;AU and perihelion greater than 30&nbsp;AU are known, which are called extreme trans-Neptunian objects (ETNOs).<ref name="Marcos2014">{{cite journal|author=C. de la Fuente Marcos|author2=R. de la Fuente Marcos|title=Extreme trans-Neptunian objects and the Kozai mechanism: signalling the presence of trans-Plutonian planets|journal=Monthly Notices of the Royal Astronomical Society|volume=443|issue=1|pages=L59–L63|arxiv=1406.0715|bibcode=2014MNRAS.443L..59D|doi=10.1093/mnrasl/slu084|date=September 1, 2014}}</ref>

Discrepancies in the early 1900s between the observed and expected orbits of Uranus and Neptune suggested that there were one or more additional planets beyond Neptune, but revised estimates of Neptune's mass from the ''Voyager 2'' flyby in 1989 showed that the problem was spurious.<ref>{{cite web|url=http://www.nasaspaceflight.com/2011/08/thirty-four-years-voyager-2-continues-explore/|title=Thirty-four years after launch, Voyager 2 continues to explore|date=August 20, 2011 |author1=Chris Gebhardt |author2=Jeff Goldader |work=NASASpaceflight}}</ref>

While the relatively dimmer bodies, as well as the population as the whole, are reddish (V−I = 0.3–0.6), the bigger objects are often more neutral in colour (infrared index V−I < 0.2). This distinction leads to suggestion that the surface of the largest bodies is covered with ices, hiding the redder, darker areas underneath.<ref name="Rabinowitz 2005">{{cite journal |first=David L. |last=Rabinowitz |first2=K. M. |last2=Barkume |first3=Michael E. |last3=Brown |first4=H. G. |last4=Roe |first5=M. |last5=Schwartz |first6=S. W. |last6=Tourtellotte |first7=C. A. |last7=Trujillo |date=2006 |title=Photometric Observations Constraining the Size, Shape, and Albedo of 2003 El<sub>61</sub>, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt |journal=Astrophysical Journal |volume=639 |issue=2 |pages=1238–1251 |doi=10.1086/499575 |arxiv = astro-ph/0509401 |bibcode = 2006ApJ...639.1238R }}</ref>

{| class="wikitable" style="text-align: center;"
|+ Mean-color indices of dynamical groups in the outer Solar System&thinsp;<ref name="Fornasier-2007">{{Cite journal
  |display-authors = 6
  |first1     = S. |last1 = Fornasier
  |first2     = E. |last2 = Dotto
  |first3     = O. |last3 = Hainaut
  |first4     = F. |last4 = Marzari
  |first5     = H. |last5 = Boehnhardt
  |first6     = F. |last6 = De Luise
  |first7     = M. A. |last7 = Barucci
  |date       = October 2007
  |title      = Visible spectroscopic and photometric survey of Jupiter Trojans: Final results on dynamical families
  |journal    = Icarus
  |volume     = 190
  |issue      = 2
  |pages      = 622–642
  |bibcode    = 2007Icar..190..622F 
  |doi        = 10.1016/j.icarus.2007.03.033
  |arxiv      = 0704.0350}}</ref>{{rp|35}}
! Color
! width= 120 | Plutinos
! width= 120 | Cubewanos
! width= 120 | Centaurs
! width= 120 | Scattered disc object (SDOs)
! width= 120 | Comets
! width= 120 | Jupiter trojans
|-
! B–V
| {{val|0.895|0.190}}
| {{val|0.973|0.174}}
| {{val|0.886|0.213}}
| {{val|0.875|0.159}}
| {{val|0.795|0.035}}
| {{val|0.777|0.091}}
|-
! V–R
| {{val|0.568|0.106}}
| {{val|0.622|0.126}}
| {{val|0.573|0.127}}
| {{val|0.553|0.132}}
| {{val|0.441|0.122}}
| {{val|0.445|0.048}}
|-
! V–I
| {{val|1.095|0.201}}
| {{val|1.181|0.237}}
| {{val|1.104|0.245}}
| {{val|1.070|0.220}}
| {{val|0.935|0.141}}
| {{val|0.861|0.090}}
|-
! R–I
| {{val|0.536|0.135}}
| {{val|0.586|0.148}}
| {{val|0.548|0.150}}
| {{val|0.517|0.102}}
| {{val|0.451|0.059}}
| {{val|0.416|0.057}}
|}
{{clear}}

==Pluto==
[[Image:La-la-me-pluto-horizon-wre0029964444-20150714.jpeg|thumb|right|250px|Pluto fills the frame in an image from NASA's New Horizons spacecraft taken July 13, when the spacecraft was 476,000 miles from the dwarf planet. Credit: NASA EPA.]]
[[Image:Pluto-11jul-color.jpg|thumb|left|250px|A composite image of Pluto from 11 July shows high-resolution black-and-white LORRI images colorized with Ralph data. Credit: NASA-JHUAPL-SWRI.]]
[[Image:Pluto and its satellites (2005) without labels.jpg|thumb|right|250px|Pluto and its satellites, Charon, Hydra and Nix are imaged with the Hubble Space Telescope. Credit: H. Weaver (JHU/APL), A. Stern (SwRI), and the HST Pluto Companion Search Team.]]
[[Image:First Views of Pluto (7544561854).jpg|left|thumb|300px|NASA's Hubble Space Telescope has obtained the clearest pictures ever of our solar system's most distant and enigmatic object: the planet Pluto. Credit: [https://www.flickr.com/people/44494372@N05 NASA on The Commons].{{tlx|free media}}]]
[[Image:Nh-plutosurface forstory.jpg|thumb|right|250px|The first close-up image of Pluto released by NASA from the New Horizons mission. Credit: NASA-JHUAPL-SWRI.]]
[[Image:Nh-pluto-mountain-range.jpg|thumb|left|250px|Another mountain range is revealed in this new image taken by New Horizons on July 14. Credit: NASA-JHUAPL-SWRI.]]
[[Image:Troughs in Sputnik Planum by LORRI.jpg|right|thumb|300px|The frozen plains of Sputnik Planum on Pluto are photographed by the LORRI instrument aboard New Horizons on 14 July 2015. Credit: NASA/JHUAPL/SwRI.{{tlx|free media}}]]
[[Image:PIA21944 - First Official Pluto Feature Names.jpg|left|thumb|300px|The International Astronomical Union (IAU) approved names of 14 surface features on Pluto in August 2017. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.{{tlx|free media}}]]
[[Draft:Pluto|Pluto]] is the second largest dwarf planet known (after Eris].

In the image on the right are shown from left to right: Pluto, Charon, Nix and Hydra.

The observations on the left by Hubble were made with the European Space Agency's Faint Object Camera.

Pluto is a very peculiar object. Its orbit is tilted and is more elliptical than the orbits of any of the other planets in the solar system. Pluto also rotates upside down with its North Pole below the plane of the solar system in the opposite sense of the Earth and most of the other planets. Pluto is smaller than our own Moon and also denser than any of its neighbors in the outer solar system.

Pluto is currently near its closest approach to the Earth in its 249 year journey around the Sun, and is approximately four and a half billion kilometers away. The bright object at the center of the frame is Pluto while Charon is the fainter object in the lower left. Charon is fainter than Pluto because it is smaller and, probably, because its surface is covered by water ice whereas Pluto is thought to be covered mainly by the more reflective methane frost or snow. As indicated in the diagram at the bottom of the photograph, Charon's orbit around Pluto is a circle seen nearly edge on from Earth, with a radius of almost twenty thousand kilometers - a distance equal to approximately one and a half times the diameter of the Earth. At the time of observation, Charon was near its maximum apparent distance from Pluto, so that its angular separation was about nine tenths of an arcsecond. Because of the peculiar orientation of the Pluto-Charon orbit with respect to our line of sight, Charon approaches to within less than one tenth of an arcsecond of Pluto every three days.

"Over the weekend, scientists discovered that it is a bit bigger than they expected. Previous estimates had put it somewhere between 715 and 746 miles, but new information suggests Pluto's radius is about 736 miles across, putting it solidly at the upper end of the estimate."<ref name=Thomsen>{{ cite book
|author=Deborah Netburn
|title=Pluto is now the most distant object ever visited by humanity
|publisher=Los Angeles Times
|location=Los Angeles, California USA
|date=14 July 2015
|url=http://touch.latimes.com/#section/-1/article/p2p-83989734/
|accessdate=2015-07-14 }}</ref>

"At heights of about 11,000 feet, the Norgay Montes [on the right] most closely approximates the height of the Rockies."<ref name=Moore>{{ cite book
|author=Jeff Moore
|title=High resolution photo shows another set of ice mountains on Pluto
|publisher=Mashable.com
|location=
|date=21 July 2015
|url=http://mashable.com/2015/07/21/nasa-more-ice-mountains-pluto/
|accessdate=2015-07-23 }}</ref>

"NASA scientists identified this newfound range of water-ice mountains [on the left] based on high-res images obtained by the New Horizons spacecraft."<ref name=Kramer>{{ cite book
|author=Miriam Kramer
|title=High resolution photo shows another set of ice mountains on Pluto
|publisher=Mashable.com
|location=
|date=21 July 2015
|url=http://mashable.com/2015/07/21/nasa-more-ice-mountains-pluto/
|accessdate=2015-07-23 }}</ref>

"The mountain range is located in the dwarf planet's heart-shaped feature, called Tombaugh Regio after Pluto's discoverer, Clyde Tombaugh. The mountains rise to about the height of the Appalachian Mountains on Earth, which reach a maximum height of about 6,000 feet."<ref name=Kramer/>

In the latest data from NASA's New Horizons spacecraft, a new close-up image of Pluto reveals a vast, craterless plain that appears to be no more than 100 million years old, and is possibly still being shaped by geologic processes. This frozen region is north of Pluto's icy mountains, in the center-left of the heart feature, informally named "Tombaugh Regio" (Tombaugh Region).

This fascinating icy plains region -- resembling frozen mud cracks on Earth -- has been informally named "Sputnik Planum" (Sputnik Plain) after the Earth's first artificial satellite. It has a broken surface of irregularly-shaped segments, roughly 12 miles (20 kilometers) across, bordered by what appear to be shallow troughs. Some of these troughs have darker material within them, while others are traced by clumps of hills that appear to rise above the surrounding terrain. Elsewhere, the surface appears to be etched by fields of small pits that may have formed by a process called sublimation, in which ice turns directly from solid to gas, just as dry ice does on Earth.

The irregular shapes may be the result of the contraction of surface materials, similar to what happens when mud dries. Alternatively, they may be a product of convection, similar to wax rising in a lava lamp. On Pluto, convection would occur within a surface layer of frozen carbon monoxide, methane and nitrogen, driven by the scant warmth of Pluto's interior.

Pluto's icy plains also display dark streaks that are a few miles long. These streaks appear to be aligned in the same direction and may have been produced by winds blowing across the frozen surface.

The names, listed below, pay homage to the underworld mythology, pioneering space missions, historic pioneers who crossed new horizons in exploration, and scientists and engineers associated with Pluto and the Kuiper Belt.

* '''Tombaugh Regio''' honors Clyde Tombaugh (1906&ndash;1997), the U.S. astronomer who discovered Pluto in 1930 from Lowell Observatory in Arizona.

* '''Burney crater''' honors Venetia Burney (1918&ndash;2009), who as an 11-year-old schoolgirl suggested the name "Pluto" for Clyde Tombaugh's newly discovered planet. Later in life she taught mathematics and economics.

* '''Sputnik Planitia''' is a large plain named for Sputnik 1, the first space satellite, launched by the Soviet Union in 1957.

* '''Tenzing Montes''' and '''Hillary Montes''' are mountain ranges honoring Tenzing Norgay (1914&ndash;1986) and Sir Edmund Hillary (1919&ndash;2008), the Indian/Nepali Sherpa and New Zealand mountaineer were the first to reach the summit of Mount Everest and return safely.

* '''Al-Idrisi Montes''' honors Ash-Sharif al-Idrisi (1100&ndash;1165/66), a noted Arab mapmaker and geographer whose landmark work of medieval geography is sometimes translated as "The Pleasure of Him Who Longs to Cross the Horizons."

* '''Djanggawul Fossae''' defines a network of long, narrow depressions named for the Djanggawuls, three ancestral beings in indigenous Australian mythology who traveled between the island of the dead and Australia, creating the landscape and filling it with vegetation.

* '''Sleipnir Fossa''' is named for the powerful, eight-legged horse of Norse mythology that carried the god Odin into the underworld.

* '''Virgil Fossae''' honors Virgil, one of the greatest Roman poets and Dante's fictional guide through hell and purgatory in the Divine Comedy.

* '''Adlivun Cavus''' is a deep depression named for Adlivun, the underworld in Inuit mythology.

* '''Hayabusa Terra''' is a large land mass saluting the Japanese spacecraft and mission (2003&ndash;2010) that performed the first asteroid sample return.

* '''Voyager Terra''' honors the pair of NASA spacecraft, launched in 1977, that performed the first "grand tour" of all four giant planets. The Voyager spacecraft are now probing the boundary between the Sun and interstellar space.

* '''Tartarus Dorsa''' is a ridge named for Tartarus, the deepest, darkest pit of the underworld in Greek mythology.

* '''Elliot crater''' recognizes James Elliot (1943&ndash;2011), an MIT researcher who pioneered the use of stellar occultations to study the solar system &ndash; leading to discoveries such as the rings of Uranus and the first detection of Pluto's thin atmosphere.
{{clear}}

==Charon==
[[Image:Charon Discovery.jpg|right|thumb|300px|A number of the images of Pluto appeared elongated. Credit: U.S. Naval Observatory.{{tlx|free media}}]]
On 22 June 1978, an astronomer at the U.S. Naval Observatory in Washington, D.C. was making routine measurements of photographic plates taken with the 1.55-meter (61-inch) Kaj Strand Astrometric Reflector at the USNO Flagstaff Station in Arizona. The purpose of these images was to refine the orbit of the far-flung planet Pluto to help compute a better ephemeris for this distant object.

Astronomer James W. Christy had noticed that a number of the images of Pluto appeared elongated, but images of background stars on the same plate did not. Other plates showed the planet as a tiny, round dot. Christy examined a number of Pluto images from the USNO archives, and he noticed the elongations again. Furthermore, the elongations appeared to change position with respect to the stars over time. After eliminating the possibility that the elongations were produced by plate defects and background stars, the only plausible explanation was that they were caused by a previously unknown moon orbiting Pluto at a distance of about 19,600 kilometers (12,100 miles) with a period of just over six days.

On 7 July 1978, the discovery was formally announced to the astronomical community and the world by the IAU Central Bureau for Astronomical Telegrams via IAU Circular 3241. The discovery received the provisional designation "1978 P 1"; Christy proposed the name "Charon", after the mythological ferryman who carried souls across the river Acheron, one of the five mythical rivers that surrounded Pluto's underworld. 

Over the course of the next several years, another USNO astronomer, the late Robert S. Harrington, calculated that Pluto and its newly-found moon would undergo a series of mutual eclipses and occultations, beginning in early 1985. On 17 February 1985 the first successful observation of one of these transits was made at with the 0.9-meter (36-inch) reflector at the University of Texas McDonald Observatory, within 40 minutes of Harrington's predicted time. The IAU Circular announcing these confirming observations was issued on 22 February 1985. With this confirmation, the new moon was officially named Charon.

Pluto was discovered at Lowell Observatory in 1930 by the late Clyde W. Tombaugh, an amateur astronomer from Kansas who was hired by the Observatory specifically to photograph the sky with a special camera and search for the planet predicted by the Observatory's founder, Percival Lowell. 

Lowell had deduced the existence of a "Planet X" by studying small anomalies in the orbits of Uranus and Neptune. As it turned out, Pluto's discovery was almost entirely serendipitous; Pluto's tiny mass was far too small to account for the anomalies, which were resolved when Voyager 2 determined more precise masses for Uranus and Neptune.

The discovery of Charon has led to a much better understanding of just how tiny Pluto is. Its diameter is about 2274 km (1413 miles), and its mass is 0.25% of the mass of the Earth. Charon has a diameter of about 1172 kilometers (728 miles) and a mass of about 22% that of Pluto. The two worlds circle their common center of mass with a period of 6.387 days and are locked in a "super-synchronous" rotation: observers on Pluto's surface would always see Charon in the same part of the sky relative to their local horizon. 

Normally Pluto is considered the most distant world in the solar system, but during the period from January 1979 until February 1999 it was actually closer to the Sun than Neptune. It has the most eccentric and inclinced orbit of any of the major planets. This orbit won't bring Pluto back to its discovery position until the year 2178! 
{{clear}}

==Plasma objects==
{{main|Plasmas/Plasma objects|Plasma objects}}
The New Horizons Particles and Plasma team has discovered a region of cold, dense ionized gas tens of thousands of miles beyond Pluto -- the planet's atmosphere being stripped away by the solar wind and lost to space.

==2015 TG387==

'''{{chem|2015 TG|387}}''' (nicknamed ''The Goblin'' for the letters ''TG'' and because its discovery was near Halloween),<ref name="Guarino2018">{{cite book 
  |last1=Guarino
  |first1=Ben
  |title=New dwarf planet spotted at the very fringe of our solar system, In: ''The Washington Post''
  |url=https://www.washingtonpost.com/science/2018/10/02/new-dwarf-planet-spotted-very-fringe-our-solar-system
  |date=October 2, 2018
  |accessdate=October 3, 2018}}</ref><ref name="NYT-20181002">{{cite book
  |last=Chang
  |first=Kenneth
  |title=A Goblin World That Points Toward Hidden Planet Nine in the Solar System, In: ''The New York Times''
  |url=https://www.nytimes.com/2018/10/02/science/goblin-planet-nine.html
  |date=October 2, 2018
  |accessdate=October 2, 2018}}</ref> is a trans-Neptunian object (TNO) and sednoid in the outermost part of the [[Solar System]].<ref name=Cbc2018-10-02> {{cite book
  |last=Mortillaro
  |first=Nicole 
  |url=https://www.cbc.ca/news/technology/planet-nine-tg387-1.4845760
  |title=Discovery of new object supports theory of 'super-Earth' at edge of solar system, In: ''CBC News''
  |date=October 2, 2018
  |accessdate=October 2, 2018}}</ref>  It was first observed on October 13, 2015, with the Subaru Telescope at Mauna Kea Observatories, and publicly announced on October 1, 2018.<ref name="MPEC2018-T05">{{Cite book
  |title=MPEC 2018-T05 : 2015 TG387
  |url=https://www.minorplanetcenter.net/mpec/K18/K18T05.html
  |publisher=IAU Minor Planet Center
  |date=October 1, 2018
  |accessdate=October 2, 2018}}</ref><ref name="Witze2018">{{cite book 
  |first=Alexandra
  |last=Witze
  |title=‘Goblin’ world found orbiting at the edges of the Solar System
  |url=https://www.nature.com/articles/d41586-018-06885-1
  |doi=10.1038/d41586-018-06885-1
  |publisher=Nature
  |date=October 1, 2018
  |accessdate=October 2, 2018}}</ref>

{{chem|2015 TG|387}} is the third sednoid to be discovered, following 90377 Sedna and {{chem|2012 VP|113}}.<ref name="Sheppard2018"/><ref name="JPL-sednoid">{{cite book 
  |title=JPL Small-Body Database Search Engine: a > 150 (AU) and q > 50 (AU) and data-arc span > 365 (d) 
  |publisher=JPL Solar System Dynamics
  |url=http://ssd.jpl.nasa.gov/sbdb_query.cgi?obj_group=all;obj_kind=all;obj_numbered=all;OBJ_field=0;ORB_field=0;combine_mode=AND;c1_group=ORB;c1_item=Bh;c1_op=%3E;c1_value=150;c2_group=ORB;c2_item=Cj;c2_op=%3E;c2_value=365;c3_group=ORB;c3_item=Bi;c3_op=%3E;c3_value=50;table_format=HTML;max_rows=100;format_option=comp;c_fields=AcBhBgBjBkBlBiBnBsCjCpAiBq;.cgifields=format_option;.cgifields=combine_mode;.cgifields=ast_orbit_class;.cgifields=obj_kind;.cgifields=table_format;.cgifields=obj_group;.cgifields=obj_numbered;.cgifields=com_orbit_class&query=1&c_sort=BiA 
  |accessdate=October 2, 2018}}</ref> It is estimated to be {{convert|300|km|mi|abbr=on}} in diameter.<ref name="Sheppard2018"/>

Along with the similar orbits of other distant TNOs, the orbit of {{chem|2015 TG|387}} suggests, but does not prove, the existence of a hypothetical Planet Nine in the outer Solar System.<ref name="Sheppard2018"/><ref name="Witze2018"/>

As of 2018, the object is 80 AU from the Sun; about two-and-a-half times farther out than Pluto’s orbit.<ref name="NYT-20181002"/> As with Sedna, it would not have been found had it not been on the inner leg of its long orbit, which suggests that there may be many similar objects, most too distant to be detected by contemporary technological methods, and implies a population of about 2 million Hills cloud, or inner Oort cloud, objects larger than {{convert|40|km|mi|abbr=on}}, with a combined total mass of 10<sup>22</sup> kg, which is several times the mass of the asteroid belt.<ref name="Sheppard2018">{{cite book
  |first1=Scott
  |last1=Sheppard
  |first2=Chadwick
  |last2=Trujillo
  |first3=David
  |last3=Tholen
  |first4=Nathan
  |last4=Kaib
  |title=A New High Perihelion Inner Oort Cloud Object
  |url=https://arxiv.org/pdf/1810.00013.pdf
  |arxiv=1810.00013
  |date=September 28, 2018
  |accessdate=October 2, 2018}}</ref>

==Cubewanos==

The classical objects (cubewanos) are very different from the scattered objects: more than 30% of all cubewanos are on low-inclination, near-circular orbits whose eccentricities peak at 0.25.<ref name="Levison2003">{{cite journal
 | last1 = Levison | first1 = Harold F. | last2 = Morbidelli | first2 = Alessandro 
 | title = The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration
 | journal = Nature
 | volume = 426 | issue = 6965 | pages = 419–421
 | date = 2003-11-27 | language =
 | url = http://www.nature.com/nature/journal/v426/n6965/abs/nature02120.html
 | doi = 10.1038/nature02120 | pmid = 14647375
 | accessdate = 2012-05-26 |bibcode = 2003Natur.426..419L }}</ref> Classical objects possess eccentricities ranging from 0.2 to 0.8. Though the inclinations of scattered objects are similar to the more extreme KBOs, very few scattered objects have orbits as close to the ecliptic as much of the KBO population.<ref name="dynam" />

Although motions in the scattered disc are random, they do tend to follow similar directions, which means that SDOs can become trapped in temporary resonances with Neptune. Examples of possible resonant orbits within the scattered disc include 1:3, 2:7, 3:11, 5:22 and 4:79.<ref name="gomes" />

==Plutinos==

The Kuiper belt is a relatively thick torus (or "doughnut") of space, extending from about 30&nbsp;to 50&nbsp;AU<ref>{{cite journal |title=Thermal Evolution and Differentiation of Edgeworth-Kuiper Belt Objects|first1=M. C. |last1=De Sanctis|first2=M. T. |last2= Capria|first3=A. |last3= Coradini|journal=The Astronomical Journal| doi= 10.1086/320385 |volume=121 |pages=2792–2799|date=2001 |bibcode=2001AJ....121.2792D |issue=5}}</ref> comprising two main populations of Kuiper belt objects (KBOs): the classical Kuiper-belt objects (or "cubewanos"), which lie in orbits untouched by Neptune, and the resonant Kuiper-belt objects; those which Neptune has locked into a precise orbital ratio such as 2:3 (the object goes around twice for every three Neptune orbits) and 1:2 (the object goes around once for every two Neptune orbits). These ratios, called orbital resonances, allow KBOs to persist in regions which Neptune's gravitational influence would otherwise have cleared out over the age of the Solar System, since the objects are never close enough to Neptune to be scattered by its gravity. Those in 2:3 resonances are known as "plutinos", because Pluto is the largest member of their group, whereas those in 1:2 resonances are known as "resonant trans-Neptunian object#1:2 resonance ("twotinos", period ~330 years) twotinos".

==Kuiper belts==
[[Image:TheKuiperBelt Projections 100AU Classical SDO.svg|thumb|right|250px|The eccentricity and inclination of the scattered-disc population compared to the classical and 5:2 resonant Kuiper-belt objects. Credit: [[c:user:Eurocommuter~commonswiki|Eurocommuter~commonswiki]].]]
[[Image:Outersolarsystem objectpositions labels comp.png|thumb|left|250px|Known objects in the Kuiper belt, are derived from data from the [[w:Minor Planet Center|Minor Planet Center]]. Credit: [[w:User:WilyD|WilyD]].]]
The '''Kuiper belt''' is a region of the solar system extending from the orbit of Neptune (at 30 AU to approximately 60 AU from the Sun.<ref name=Stern>{{ cite journal
| author=Alan Stern
| title=Collisional Erosion in the Primordial Edgeworth-Kuiper Belt and the Generation of the 30–50 AU Kuiper Gap
| journal=The Astrophysical Journal
| volume=490
| issue=2
| pages=879–882
| year=1997
| doi=10.1086/304912
| last2=Colwell | first2=Joshua E.
| bibcode=1997ApJ...490..879S }}</ref> It consists mainly of [[w:small Solar System body|small bodies]].

"[B]roadband optical photometry of Centaurs and Kuiper Belt objects from the Keck 10 m, the University of Hawaii 2.2 m, and the Cerro Tololo InterAmerican (CTIO) 1.5 m telescopes [shows] a wide dispersion in the optical colors of the objects, indicating nonuniform surface properties. The color dispersion [may] be understood in the context of the expected steady reddening due to bombardment by the ubiquitous flux of cosmic rays."<ref name="Luu">{{cite journal
|author=Jane Luu and David Jewitt
|title=Color Diversity among the Centaurs and Kuiper Belt Objects
|journal=The Astronomical Journal
|month=November
|year=1996
|volume=112
|issue=5
|pages=2310-8
|url=http://adsabs.harvard.edu/full/1996AJ....112.2310L
|arxiv=
|bibcode=1996AJ....112.2310L
|doi=
|pmid=
|accessdate=2013-11-05 }}</ref>

In the image at right, objects in the main part of the Kuiper belt are coloured green, while scattered objects are coloured orange. The four outer planets are blue. Neptune's few known [[w:Neptune trojan|trojans]] are yellow, while Jupiter's are pink. The scattered objects between Jupiter's orbit and the Kuiper belt are known as [[w:Centaur (minor planet)|centaurs]]. The scale is in [[w:astronomical unit|astronomical unit]]s. The pronounced gap at the bottom is due to difficulties in detection against the background of the plane of the [[w:Milky Way|Milky Way]].

Legend:

*<span style="color:red;background-color:black;padding:4px">Red</span> = [[Stars/Sun|The Sun]]

*<span style="color:aquamarine;background-color:black;padding:3px">Aquamarine</span> = [[w:Gas giant|Giant Planet]]

*<span style="color:lime;background-color:black;padding:3px">Lime Green</span> = [[w:Kuiper belt object|Kuiper belt object]]

*<span style="color:Orange;background-color:black;padding:3px">Orange</span> = [[w:Scattered disc object|Scattered disc object]] or [[w:Centaur (planetoid)|Centaur]]

*<span style="color:Magenta;background-color:black;padding:3px">Magenta</span> = [[w:Jupiter Trojan|Trojan of Jupiter]]

*<span style="color:Yellow;background-color:black;padding:3px">Yellow</span> = [[w:Neptune trojan|Trojan of Neptune]]

Axes list distances in [[w:Astronomical unit|AU]], projected onto the [[w:ecliptic|ecliptic]], with [[w:ecliptic longitude|ecliptic longitude]] zero being to the right, along the "x" axis). 

Positions are accurate for January 1st, 2000 ([[w:eEpoch (astronomy)#J2000.0|J2000 epoch]]) with some caveats:

For planets, positions should be exact.

For minor bodies, positions are extrapolated from other epochs assuming purely [[w:eosculating orbit|Keplerian motion]]. As all data is from an epoch between 1993 and 2007, this should be a reasonable approximation.

Data from the [[w:Minor Planet Center|Minor Planet Center]]<ref name=mpc>{{ cite book
|url=http://www.cfa.harvard.edu/iau/MPCORB.html
|title=The MPC Orbit (MPCORB) Database }}</ref> or Murray and Dermott<ref name=murraydermott>{{ cite book
|author=Carl D. Murray and Stanley F. Dermott
|title=Solar System Dynamics
|publisher=Cambridge University Press
|year=1999
|isbn=0 521 57295.9 }}</ref> as needed.

Radial "spokes" of higher density in this image, or gaps in particular directions are due to observational bias (i.e. where objects were searched for), rather than any real physical structure. The pronounced gap at the bottom is due to obscuration by the band of the Milky Way.
{{clear}}

==1995 TL 95==

The first object presently classified as an SDO to be discovered was 1995 TL<sub>8</sub>, found in 1995 by Spacewatch.<ref>Schmadel, Lutz D. (2003); ''Dictionary of Minor Planet Names'' (5th rev. and enlarged ed. edition). Berlin: Springer. Page 925 (Appendix 10). Also see McFadden, Lucy-Ann; Weissman, Paul & Johnson, Torrence (1999). ''Encyclopedia of the Solar System''. San Diego: Academic Press. Page 218.</ref>

==1996 TL 96==

The first scattered-disc object (SDO) to be recognised as such was 1996 TL<sub>66</sub>,<ref>{{cite journal |first=Jane X. |last=Luu |first2=Brian G. |last2=Marsden |first3=David C. |last3=Jewitt |date=5 June 1997 |url=http://www2.ess.ucla.edu/~jewitt/papers/TL66_1996/TL66.pdf|title=A new dynamical class of object in the outer Solar System|journal=Nature|volume=387| doi=10.1038/42413|accessdate=2008-08-02|pages=573–575|archiveurl = https://web.archive.org/web/20070812095854/http://www.ifa.hawaii.edu/faculty/jewitt/papers/TL66_1996/TL66.pdf |archivedate = August 12, 2007|bibcode = 1997Natur.387..573L|issue=6633}}</ref><ref name="Davies1">{{cite book |title=Beyond Pluto: Exploring the Outer Limits of the Solar System |publisher=Cambridge University Press |first=John Keith |last=Davies |date=2001 |url=http://assets.cambridge.org/97805218/00198/frontmatter/9780521800198_frontmatter.pdf |accessdate=2008-07-02 |isbn=978-0-521-80019-8 |page=111 }}</ref> originally identified in 1996 by astronomers based at Mauna Kea in Hawaii.

==1999 CV 118==

Three more were identified by the same survey in 1999: 1999 CV<sub>118</sub>, 1999 CY<sub>118</sub>, and 1999 CF<sub>119</sub>.<ref name="jewitt2000" />

==2011 SDOs==

As of 2011, over 200 SDOs have been identified,<ref name="MPC" /> including 229762 Gǃkúnǁʼhòmdímà|Gǃkúnǁʼhòmdímà (discovered by Schwamb, Brown, and Rabinowitz),<ref>{{cite journal|title=2007 UK126|bibcode=2008MPEC....D...38S|author1=Schwamb|first1=M. E.|last2=Brown |first2=Michael E. |last3=Rabinowitz |first3=Davdi |last4=Marsden |first4=Brian G. |date=2008|pages=38|journal=Minor Planet Electronic Circ.|volume=2008-D38}}</ref> 2002 TC<sub>302</sub> (Near Earth Asteroid Tracking NEAT), Eris (Brown, Trujillo, and Rabinowitz),<ref>{{cite web| author=Staff| date=2007-05-01| url=http://www.minorplanetcenter.org/iau/lists/NumberedMPs.html| title=Discovery Circumstances: Numbered Minor Planets| publisher=Minor Planet Center| accessdate=2010-10-25 }}</ref> 90377 Sedna Sedna (Brown, Trujillo, and Rabinowitz)<ref>{{cite web |title=Discovery Circumstances: Numbered Minor Planets (90001)-(95000) |publisher=Minor Planet Center |url=http://www.minorplanetcenter.org/iau/lists/NumberedMPs090001.html |accessdate=2010-10-25}}</ref> and 2004 VN<sub>112</sub> (Deep Ecliptic Survey).<ref>{{cite web |author=Marc W. Buie  |date=2007-11-08 |title=Orbit Fit and Astrometric record for 04VN112 |publisher=SwRI (Space Science Department) |url=http://www.boulder.swri.edu/~buie/kbo/astrom/04VN112.html |accessdate=2008-07-17 |deadurl=yes |archiveurl=https://web.archive.org/web/20100818145946/http://www.boulder.swri.edu/~buie/kbo/astrom/04VN112.html |archivedate=2010-08-18 |df= }}</ref> Although the numbers of objects in the Kuiper belt and the scattered disc are hypothesized to be roughly equal, observational bias due to their greater distance means that far fewer SDOs have been observed to date.<ref name="dynam">{{cite book |title=Encyclopedia of the Solar System |chapter=Comet Populations and Cometary Dynamics |first=Harold F. |last=Levison |first2=Luke |last2=Donnes |publisher=Academic Press |date=2007 |editor-first1=Lucy Ann |editor-last1=Adams McFadden |editor-first2=Paul Robert |editor-last2=Weissman |editor-first3=Torrence V. |editor-last3=Johnson |edition=2nd |location=Amsterdam; Boston |isbn=978-0-12-088589-3 |pages=575–588 |chapter-url=http://astropolis.pl/index.php?app=core |deadurl=yes |archiveurl=https://www.webcitation.org/6bKfm5Rw5?url=http://astropolis.pl/index.php?app=core&module=attach&section=attach&attach_id=38054 |archivedate=2015-09-06 |df= }}</ref>

==Oort clouds==
{{multiple image
 |direction = vertical
 |align = right
 |width = 285
 |image1=PIA17046 - Voyager 1 Goes Interstellar.jpg
 |image2=Kuiper oort-en.svg
 |caption1=This graphic shows the distance from the Oort cloud to the rest of the Solar System and two of the nearest stars measured in astronomical units (AU). The scale is logarithmic, with each specified distance ten times further out than the previous one.
 |caption2=An artist's rendering is of the Oort cloud and the Kuiper belt (inset). Sizes of individual objects have been exaggerated for visibility.
}}
The '''Oort cloud''' or the '''Öpik–Oort cloud'''<ref name = "Whipple">{{ cite journal
| author = Fred Lawrence Whipple, G. Turner, J. A. M. McDonnell, M. K. Wallis 
| title = A Review of Cometary Sciences
| url = http://rsta.royalsocietypublishing.org/content/323/1572/339.short
| journal = Philosophical Transactions of the Royal Society A
| volume = 323
| issue = 1572
| pages = 339–347 [341]
| publisher = Royal Society Publishing
| date = 1987-09-30
| bibcode = 1987RSPTA.323..339W
| doi = 10.1098/rsta.1987.0090 }}</ref> is a hypothesized spherical cloud of [[Draft:Comets|comets]] which may lie roughly 50,000 [[w:astronomical unit|AU]], or nearly a [[w:light-year|light-year]], from the [[Stars/Sun|Sun]].<ref name="Morbidelli2006">{{ cite book
|author=Alessandro Morbidelli
|year=2006
|title=Origin and dynamical evolution of comets and their reservoirs of water ammonia and methane.
|url=https://arxiv.org/abs/astro-ph/0512256
|arxiv=astro-ph/0512256 }}</ref> This places the cloud at nearly a quarter of the distance to [[w:Proxima Centauri|Proxima Centauri]], the nearest [[w:star|star]] to the Sun. The outer limit of the Oort cloud defines the [[w:Cosmography|cosmographical]] boundary of the [[Solar System]] and the region of the Sun's gravitational dominance.<ref name="NASA_SSE_oort">{{ cite book
|title=Kuiper Belt & Oort Cloud
|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs&Display=OverviewLong
|publisher=NASA
|accessdate=2011-08-08 }}</ref>

Known trans-Neptunian objects are often divided into two subpopulations: the Kuiper belt and the scattered disc.<ref name="MorbidBrown">{{cite book |first=Alessandro |last=Morbidelli |first2=Michael E. |last2=Brown |title=Comets II|editor= M. C. Festou|editor2= H. U. Keller|editor3= H. A. Weaver |publisher=University of Arizona Press |location=Tucson (AZ) |date=2004-11-01 |pages=175–91 |chapter=The Kuiper Belt and the Primordial Evolution of the Solar System |isbn=978-0-8165-2450-1 |oclc=56755773 |chapter-url=http://www.lpi.usra.edu/books/CometsII/7004.pdf |accessdate=2008-07-27 }}</ref> A third reservoir of trans-Neptunian objects, the Oort cloud, has been hypothesized, although no confirmed direct observations of the Oort cloud have been made.<ref name= Morbidelli2008>{{cite arXiv |title=Origin and dynamical evolution of comets and their reservoirs |first=Alessandro |last= Morbidelli |eprint=astro-ph/0512256 |date=2005}}</ref> Some researchers further suggest a transitional space between the scattered disc and the inner Oort cloud, populated with "detached objects".<ref name= gomes />
{{clear}}

==Neptune objects==

In contrast to the Kuiper belt, the scattered-disc population can be disturbed by Neptune.<ref name="dynam2">{{cite book | title = Encyclopedia of the Solar System | chapter = Kuiper Belt Dynamics | first=Alessandro |last=Morbidelli | first2=Harold F. |last2=Levison |publisher = Academic Press | date = 2007 | editor = Lucy-Ann Adams McFadden | editor2 = Paul Robert Weissman | editor3 = Torrence V. Johnson | edition = 2nd | location = Amsterdam; Boston | isbn = 978-0-12-088589-3 | pages = 589–604}}</ref> Scattered-disc objects come within gravitational range of Neptune at their closest approaches (~30&nbsp;AU) but their farthest distances reach many times that.<ref name=gomes>{{cite web|title=The Scattered Disk: Origins, Dynamics and End States|first=Rodney S. |last=Gomes |first2=Julio A. |last2=Fernandez |first3=Tabare |last3=Gallardo |first4=Adrian |last4=Brunini |work=Universidad de la Republica, Uruguay |url=http://www.fisica.edu.uy/~gallardo/scatdisk.pdf |date= 2008 |accessdate=2008-08-10 }}</ref> Ongoing research<ref name=horner2003>{{cite journal|title=The Populations of Comet-like Bodies in the Solar System|last1=Horner|first1=J.|last2=Evans|first2=N. W.|last3=Bailey|first3=Mark E.|last4=Asher|first4=D. J.|journal=Monthly Notices of the Royal Astronomical Society|volume=343|pages=1057–1066|date=2003|doi=10.1046/j.1365-8711.2003.06714.x|arxiv=astro-ph/0304319|bibcode=2003MNRAS.343.1057H|issue=4}}</ref> suggests that the centaurs, a class of icy planetoids that orbit between Jupiter and Neptune, may simply be SDOs thrown into the inner reaches of the Solar System by Neptune, making them "cis-Neptunian" rather than trans-Neptunian scattered objects.<ref>Remo notes that Cis-Neptunian bodies "include terrestrial and large gaseous planets, planetary moons, asteroids, and main-belt comets within Neptune's orbit." (Remo 2007)</ref> Some objects, like (29981) 1999 TD<sub>10</sub>, blur the distinction<ref>{{cite web|title=New Object in Solar System Defies Categories |first= Kenneth | last= Silber |work=space.com |date=1999 |url=http://www.space.com/scienceastronomy/solarsystem/centaur_disc_991111.html |accessdate=2008-08-12 |deadurl=yes |archiveurl=https://web.archive.org/web/20050921034710/http://www.space.com/scienceastronomy/solarsystem/centaur_disc_991111.html |archivedate= September 21, 2005 }}</ref> and the Minor Planet Center (MPC), which officially catalogues all trans-Neptunian objects, now lists centaurs and SDOs together.<ref name= MPC />

The MPC, however, makes a clear distinction between the Kuiper belt and the scattered disc, separating those objects in stable orbits (the Kuiper belt) from those in scattered orbits (the scattered disc and the centaurs).<ref name= MPC>{{cite web
|url= http://www.minorplanetcenter.org/iau/lists/Centaurs.html |title= List Of Centaurs and Scattered-Disk Objects |publisher= Central Bureau for Astronomical Telegrams, Harvard-Smithsonian Center for Astrophysics|date= 2011-01-03 |author= IAU: Minor Planet Center
|accessdate=2011-01-03}}</ref> However, the difference between the Kuiper belt and the scattered disc is not clear-cut, and many astronomers see the scattered disc not as a separate population but as an outward region of the Kuiper belt. Another term used is "scattered Kuiper-belt object" (or SKBO) for bodies of the scattered disc.<ref>{{cite web
|date=2008 |first=David C. |last=Jewitt |title= The 1000&nbsp;km Scale KBOs |url= http://www2.ess.ucla.edu/~jewitt/kb/big_kbo.html|accessdate=2010-01-23}}</ref>

The difference between objects in the Kuiper belt and scattered-disc objects is that the latter bodies "are transported in semi-major axis by close and distant encounters with Neptune,"<ref name= MorbidBrown /> but the former experienced no such close encounters. This delineation is inadequate (as they note) over the age of the Solar System, since bodies "trapped in resonances" could "pass from a scattering phase to a non-scattering phase (and vice versa) numerous times."<ref name= MorbidBrown /> That is, trans-Neptunian objects could travel back and forth between the Kuiper belt and the scattered disc over time. Therefore, they chose instead to define the regions, rather than the objects, defining the scattered disc as "the region of orbital space that can be visited by bodies that have encountered Neptune" within the radius of a Hill sphere, and the Kuiper belt as its "complement&nbsp;... in the ''a'' > 30&nbsp;AU region"; the region of the Solar System populated by objects with semi-major axes greater than 30&nbsp;AU.<ref name= MorbidBrown />

The scattered disc is a very dynamic environment.<ref name="dynam" /> Because they are still capable of being perturbed by Neptune, SDOs' orbits are always in danger of disruption; either of being sent outward to the Oort cloud or inward into the centaur population and ultimately the Jupiter family of comets.<ref name="dynam" /> For this reason Gladman et al. prefer to refer to the region as the scattering disc, rather than scattered.<ref name="ArizonaBook_Gladman2007" /> Unlike Kuiper-belt objects (KBOs), the orbits of scattered-disc objects can be inclined as much as 40° from the ecliptic.<ref name="Bertoldi Altenhoff et al. 2006">{{cite journal| doi = 10.1038/nature04494| last1 = Bertoldi | first1 = F.| last2 = Altenhoff | first2 = W.| last3 = Weiss | first3 = A.| last4 = Menten | first4 = K. M.| last5 = Thum | first5 = C.| date = 2 February 2006| title = The trans-Neptunian object UB<sub>313</sub> is larger than Pluto| journal = Nature| volume = 439| issue = 7076| pages = 563–564| pmid = 16452973| pmc = | bibcode = 2006Natur.439..563B| ref = {{sfnRef|Bertoldi Altenhoff et al.|2006}}
}}</ref>

==Sedna==
[[Image:Oort cloud Sedna orbit.svg|thumb|right|250px|Here, the presumed distance of the Oort cloud is compared to the rest of the Solar System using the orbit of Sedna. Credit: NASA / JPL-Caltech / R. Hurt.]]
[[Image:Sedna-NASA.JPG|thumb|left|250px|Sedna, a possible inner Oort cloud object, is a discovery in 2003. Credit: NASA/Caltech.]]
Sedna was discovered from an image dated [http://www.boulder.swri.edu/%7Ebuie/kbo/astrom/90377.html 2003-11-14 at coordinates 03 15 10.09 +05 38 16.5]. The 3 overexposed stars are apparent magnitude 13. The "bright star" near Sedna is apmag 14.9 and about the same magnitude as Pluto. [http://www.wikisky.org/?ra=3.2528028&de=5.637916600000001&zoom=9&show_grid=1&show_constellation_lines=1&show_constellation_boundaries=1&show_const_names=0&show_galaxies=1&show_box=1&box_ra=3.2528028&box_de=5.6379166&box_width=50&box_height=50&img_source=DSS2 (Wikisky image of this region)] The picture shows an area of the sky equal to the area covered by a pinhead held at arm's length. Sedna is too faint to be seen by all but the most powerful amateur telescopes.

The Minor Planet Center classifies the trans-Neptunian object 90377 Sedna as a scattered-disc object. Sedna should be considered an inner Oort-cloud object rather than a member of the scattered disc, because, with a perihelion distance of 76 AU, it is too remote to be affected by the gravitational attraction of the outer planets.
<ref name="Sedna">{{cite web|title= Sedna (The coldest most distant place known in the solar system; possibly the first object in the long-hypothesized Oort cloud) |first= Michael E. |last= Brown |publisher= California Institute of Technology, Department of Geological Sciences |url=http://www.gps.caltech.edu/~mbrown/sedna/ |accessdate=2008-07-02}}</ref> Under this definition, an object with a perihelion greater than 40&nbsp;AU could be classified as outside the scattered disc.
<ref name="Kobe">{{cite journal
|title= Dynamical classification of trans-Neptunian objects: Probing their origin, evolution, and interrelation 
|first1 =Patryk Sofia | last1= Lykawka |first2=Tadashi | last2= Mukai
|place=Kobe |volume=189 |issue=1|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4MY0MMW-3&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=263a1288080d4fc7cd1d53d76f7dc580
|archive-url=https://web.archive.org/web/20110310063719/http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4MY0MMW-3&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=263a1288080d4fc7cd1d53d76f7dc580
|dead-url=yes
|archive-date=2011-03-10
|accessdate=2008-07-24|pages=213–232
|doi=10.1016/j.icarus.2007.01.001
|bibcode=2007Icar..189..213L
|date=2007
|journal=Icarus}}</ref>
{{clear}}

==2000 CR 105==

(148209) 2000 CR<sub>105</sub> (discovered before Sedna) and 2004 VN<sub>112</sub> have a perihelion too far away from Neptune to be influenced by it. This led to a discussion among astronomers about a new minor planet set, called the ''extended scattered disc'' ('''E-SDO''').<ref>{{cite web|url=http://www.obs-nice.fr/gladman/cr105.html|title=Evidence for an Extended Scattered Disk? |work=Observatoire de la Cote d'Azur |first=Brett J. |last=Gladman |accessdate=2008-08-02}}</ref> 2000 CR<sub>105</sub> may also be an inner Oort-cloud object or (more likely) a transitional object between the scattered disc and the inner Oort cloud. More recently, these objects have been referred to as ''"detached"'',<ref name= Jewitt2006>{{cite book|first= David C. |last= Jewitt |first2=A. |last2=Delsanti | chapter=The Solar System Beyond The Planets| title=Solar System Update : Topical and Timely Reviews in Solar System Sciences| publisher=Springer-Praxis Ed.| isbn= 978-3-540-26056-1| date=2006}} ([http://www2.ess.ucla.edu/~jewitt/papers/2006/DJ06.pdf Preprint version (pdf)])</ref> or ''distant detached objects'' ('''DDO''').<ref name="Gomez 2006" />

There are no clear boundaries between the scattered and detached regions.<ref name="Kobe" /> Gomes et al. define SDOs as having "highly eccentric orbits, perihelia beyond Neptune, and semi-major axes beyond the 1:2 resonance." By this definition, all distant detached objects are SDOs.<ref name="gomes" /> Since detached objects' orbits cannot be produced by Neptune scattering, alternative scattering mechanisms have been put forward, including a passing star<ref name="Morbidelli2004">{{cite journal |journal=The Astronomical Journal |issue=5 |volume=128 |pages=2564–2576 |date=November 2004 |title=Scenarios for the Origin of the Orbits of the Trans-Neptunian Objects 2000 CR<sub>105</sub> and 2003 VB<sub>12</sub> |first=Alessandro |last=Morbidelli |first2=Harold F. |last2=Levison |url=http://www.iop.org/EJ/abstract/1538-3881/128/5/2564/ |doi=10.1086/424617 |accessdate=2008-07-02 |bibcode=2004AJ....128.2564M |arxiv = astro-ph/0403358 }}</ref> or a distant, planet-sized object.<ref name="Gomez 2006" >{{cite journal|bibcode=2006Icar..184..589G|title=A distant planetary-mass solar companion may have produced distant detached objects|first=Rodney S. |last=Gomes |first2=John J. |last2=Matese |first3=Jack J. |last3=Lissauer |journal=Icarus |volume=184 |issue=2 |pages=589–601 |date=October 2006 |doi=10.1016/j.icarus.2006.05.026 }}</ref>

==Scattered near objects==

''Scattered-near'' (i.e. typical SDOs) and ''scattered-extended'' (i.e. detached objects),<ref name="DES_Elliot2006">{{cite journal|first1=J. L. |last1= Elliot|first2= S. D. |last2= Kern| first3=K. B. | last3= Clancy ''et al.''|title=The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population|journal=The Astronomical Journal|volume=129|date=2005|url=http://iopscience.iop.org/1538-3881/129/2/1117/pdf/1538-3881_129_2_1117.pdf| pages=1117–1162|doi=10.1086/427395|archiveurl = https://web.archive.org/web/20080625140652/http://alpaca.as.arizona.edu/~trilling/des2.pdf |archivedate = June 25, 2008|deadurl=no|bibcode=2005AJ....129.1117E|issue=2}}</ref> where scattered-near objects are those whose orbits are non-resonant, non-planetary-orbit-crossing and have a Tisserand parameter (relative to Neptune) less than 3,<ref name="DES_Elliot2006" /> and scattered-extended objects have a Tisserand parameter (relative to Neptune) greater than 3 and have a time-averaged eccentricity greater than 0.2.<ref name="DES_Elliot2006" />

==10-million-year orbits==

A 10-million-year orbit integration is used instead of the Tisserand parameter.<ref name="ArizonaBook_Gladman2007"/> An object qualifies as an SDO if its orbit is not resonant, has a semi-major axis no greater than 2000 AU, and, during the integration, its semi-major axis shows an excursion of 1.5 AU or more.<ref name="ArizonaBook_Gladman2007" /> Gladman et al. suggest the term ''scattering disk object'' to emphasize this present mobility.<ref name="ArizonaBook_Gladman2007" /> If the object is not an SDO as per the above definition, but the eccentricity of its orbit is greater than 0.240, it is classified as a ''detached TNO''.<ref name="ArizonaBook_Gladman2007" /> (Objects with smaller eccentricity are considered classical.) In this scheme, the disc extends from the orbit of Neptune to 2000 AU, the region referred to as the inner Oort cloud.

==Medium and high eccentricities==

SDOs are typically characterized by orbits with medium and high eccentricities with a semi-major axis greater than 50&nbsp;AU, but their perihelia bring them within influence of Neptune.<ref name="tjl2000">{{cite journal |first=Chadwick A. |last=Trujillo |first2=David C. |last2=Jewitt |first3=Jane X. |last3=Luu |title=Population of the Scattered Kuiper Belt |journal=The Astrophysical Journal |volume=529 |pages=L103–L106 |date=2000-02-01 |url=http://www2.ess.ucla.edu/~jewitt/papers/SKBO/tjl2000.pdf  |accessdate=2008-07-02 |doi=10.1086/312467 |pmid= 10622765 |issue= 2 |archiveurl = https://web.archive.org/web/20070812095910/http://www.ifa.hawaii.edu/faculty/jewitt/papers/SKBO/tjl2000.pdf |archivedate = August 12, 2007 |bibcode=2000ApJ...529L.103T|arxiv = astro-ph/9912428 }}</ref> Having a perihelion of roughly 30&nbsp;AU is one of the defining characteristics of scattered objects, as it allows Neptune to exert its gravitational influence.<ref name="jewitt2000">{{cite web |date=August 2009 |title=Scattered Kuiper Belt Objects (SKBOs) |publisher=Institute for Astronomy |first=David C. |last=Jewitt |url=http://www2.ess.ucla.edu/~jewitt/kb/kb-scattered.html |accessdate=2010-01-23 }}</ref>

==Eris==
[[Image:Eris and dysnomia2.jpg|right|thumb|250px|The dwarf planet Eris is the largest known scattered-disc object (center), with its moon Dysnomia (left of object). Credit: NASA, ESA, and [[w:user:Michael E. Brown|Michael E. Brown]].]]
136199 Eris was measured to be {{convert|2326|±|12|km|sp=us}} in diameter.<ref name="sicardy">
{{cite journal
| title = Size, density, albedo and atmosphere limit of dwarf planet Eris from a stellar occultation
| journal = European Planetary Science Congress Abstracts
| volume = 6
| date = 2011
| url = http://meetingorganizer.copernicus.org/EPSC-DPS2011/EPSC-DPS2011-137-8.pdf
| accessdate = September 14, 2011
| bibcode = 2011epsc.conf..137S
| last1 = Sicardy
| first1 = B.
| last2 = Ortiz
| first2 = J. L.
| last3 = Assafin
| first3 = M.
| last4 = Jehin
| first4 = E.
| last5 = Maury
| first5 = A.
| last6 = Lellouch
| first6 = E.
| last7 = Gil-Hutton
| first7 = R.
| last8 = Braga-Ribas
| first8 = F.
| last9 = Colas
| first9 = F.
| page = 137
| author10 = Widemann }}</ref> Eris's mass is about 0.27% of the Earth mass,<ref name="Brown Schaller 2007">{{cite journal| doi = 10.1126/science.1139415| last1 = Brown| first1 = Michael E.| last2 = Schaller| first2 = Emily L.| date = 15 June 2007| title = The Mass of Dwarf Planet Eris| journal = Science| volume = 316| issue = 5831| page = 1585| pmid = 17569855| pmc = | bibcode = 2007Sci...316.1585B| ref = harv | url= http://hubblesite.org/pubinfo/pdf/2007/24/pdf.pdf}} <!-- {{sfn|Brown Schaller|2007}} -->
</ref><ref name="070614_eris_mass">
{{cite web
| title = Dwarf Planet Outweighs Pluto
| url = http://www.space.com/scienceastronomy/070614_eris_mass.html
| work = space.com
| date = 2007
| accessdate = June 14, 2007
}}
</ref> about 27% more than dwarf planet Pluto, although Pluto is slightly larger by volume.<ref name="NASA Pluto larger 2015">{{cite web
| title = How Big Is Pluto? New Horizons Settles Decades-Long Debate
| url = http://www.nasa.gov/feature/how-big-is-pluto-new-horizons-settles-decades-long-debate
| work = www.nasa.gov
| date = 2015
| accessdate = July 14, 2015
}}</ref>

Eris is a trans-Neptunian object (TNO), a member of a high-orbital eccentricity population known as the scattered disk, with one known natural satellite, Dysnomia, at a distance from the Sun of {{convert|96.3|AU}},<ref name="AstDysEris">
{{cite web
| title = AstDys (136199) Eris Ephemerides
| publisher = Department of Mathematics, University of Pisa, Italy
| url = http://hamilton.dm.unipi.it/astdys/index.php?pc=1.1.3.0&n=Eris
| accessdate = February 28, 2016
}}
</ref> roughly three times that of Pluto. With the exception of some long-period comets, until 2018 VG<sub>18</sub> was discovered on December 17, 2018, Eris and Dysnomia were the most distant known natural objects in the Solar System.<ref name="AstDysEris" />

Observations of a stellar occultation by Eris in 2010 showed that its diameter was {{convert|2326|±|12|km|sp=us}}, very slightly less than Pluto,<ref name="Brown2010-occult">
{{cite web
| last = Brown
| first = Mike
| date = 2010
| title = The shadowy hand of Eris
| publisher = Mike Brown's Planets
| url = http://www.mikebrownsplanets.com/2010/11/shadowy-hand-of-eris.html
| accessdate = November 7, 2010 }}</ref><ref name="Brown2010-Plutosize">{{cite web
| last = Brown
| first = Mike
| date = November 22, 2010
| title = How big is Pluto, anyway?
| publisher = Mike Brown's Planets
| url = http://www.mikebrownsplanets.com/2010/11/how-big-is-pluto-anyway.html
| accessdate = November 23, 2010}} [http://tech.groups.yahoo.com/group/mpml/message/24568 (Franck Marchis on 2010-11-08)]</ref> which was measured by ''New Horizons'' as {{convert|2376.6|±|3.6|km|sp=us}} in July 2015.<ref name="Measurement">{{cite web|url=http://www.nasa.gov/feature/how-big-is-pluto-new-horizons-settles-decades-long-debate/ |title=How Big Is Pluto? New Horizons Settles Decades-Long Debate|year=2015|accessdate=2015-07-13|publisher=[[NASA]]}}</ref><ref name = "Pluto System after New Horizons">{{Cite journal|last=Stern |first=S. A. |last2=Grundy |first2=W. |last3=McKinnon |first3=W. B. |last4=Weaver |first4=H. A. |last5=Young |first5=L. A.|title=The Pluto System After New Horizons|journal=Annual Review of Astronomy and Astrophysics |volume=2018 |pages=357–392 |arxiv=1712.05669 |year=2017 |doi=10.1146/annurev-astro-081817-051935 }}</ref>

Eris is a trans-Neptunian dwarf planet (plutoid).<ref name="plutoid">{{cite web
| url = http://www.space.com/scienceastronomy/080611-plutoid-planets.html
| title = Pluto Now Called a Plutoid
| work = Space.com
| date = June 11, 2008
| accessdate = June 11, 2008 }}</ref> Its orbital characteristics more specifically categorize it as a scattered-disk object (SDO), or a TNO that has been "scattered" from the Kuiper belt into more-distant and unusual orbits following gravitational interactions with [[Neptune]] as the [[Solar System]] was forming. Although its high orbital inclination is unusual among the known SDOs, theoretical models suggest that objects that were originally near the inner edge of the Kuiper belt were scattered into orbits with higher inclinations than objects from the outer belt.<ref name="GallardoBrunini">{{cite journal
| title = On the origin of the High-Perihelion Scattered Disk: the role of the Kozai mechanism and mean motion resonances
|author1=Gomes R. S. |author2=Gallardo T. |author3=Fernández J. A. |author4=Brunini A. | journal = Celestial Mechanics and Dynamical Astronomy
| date = 2005
| volume = 91
| issue = 1–2
| pages = 109–129
| doi = 10.1007/s10569-004-4623-y
| bibcode = 2005CeMDA..91..109G }}</ref>
{{clear}}

==Haumea==
[[Image:Haumea Hubble.png|right|thumb|300px|Hubble Space Telescope image of Haumea (center) and its two moons; Hiʻiaka is above Haumea and Namaka is below. Credit: [[c:user:Renerpho|Renerpho]].{{tlx|free media}}]]
[[Image:Quaoar Haumea Makemake orbits 2018.png|left|320px|thumb|Haumea's orbit outside of Neptune is similar to Makemake's. The positions are as of 1 January 2018. Credit: [[c:user:Tomruen|Tomruen]].{{tlx|free media}}]]
Haumea (minor-planet designation 136108 Haumea, initially, (136108) 2003&nbsp;EL<sub>61</sub>) is a dwarf planet located beyond Neptune's orbit.<ref name="iau">{{cite news
 |url         = http://www.iau.org/public_press/news/detail/iau0807/
 |title       = IAU names fifth dwarf planet Haumea
 |publisher   = IAU Press Release
 |date        = 2008-09-17
 |accessdate  = 2008-09-17
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20110702012624/http://iau.org/public_press/news/detail/iau0807/
 |archivedate = 2011-07-02
 |df          = }}</ref> It was discovered on December 28, 2004, just after Christmas,<ref name="Santa2005">{{cite web
 |title       = Santa et al.
 |date        = 2005-09-10
 |publisher   = NASA Astrobiology Magazine
 |url         = http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1707&mode=thread&order=0&thold=0
 |accessdate  = 2008-10-16
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20060426180434/http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1707&mode=thread&order=0&thold=0
 |archivedate = 2006-04-26
 |df          = }}</ref> at the Palomar Observatory.<ref name="trail">
{{cite web
 |author      = Michael E Brown
 |url         = http://www.gps.caltech.edu/~mbrown/planetlila/ortiz/
 |title       = The electronic trail of the discovery of 2003&nbsp;EL<sub>61</sub>
 |work        = CalTech
 |accessdate  = 2006-08-16
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20060901181611/http://www.gps.caltech.edu/~mbrown/planetlila/ortiz/
 |archivedate = 2006-09-01
 |df          = 
}}</ref> Precovery images of Haumea have been identified back to March 22, 1955.<ref name="jpldata2014">{{cite web
 |type        = 2014-11-28 last obs
 |title       = Jet Propulsion Laboratory Small-Body Database Browser: 136108 Haumea (2003&nbsp;EL<sub>61</sub>)
 |publisher   = NASA's Jet Propulsion Laboratory
 |url         = http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=136108
 |accessdate  = 2015-01-08
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20151227152421/http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=136108
 |archivedate = 2015-12-27
 |df          = }}</ref>

Haumea is a plutoid, a dwarf planet located beyond Neptune's orbit.<ref name="usgs">
{{cite news
 |publisher   = US Geological Survey Gazetteer of Planetary Nomenclature
 |title       = Dwarf Planets and their Systems
 |url         = http://planetarynames.wr.usgs.gov/append7.html#DwarfPlanets
 |accessdate  = 2008-09-17
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20110629193230/http://planetarynames.wr.usgs.gov/Page/Planets#DwarfPlanets
 |archivedate = 2011-06-29
 |df          = 
}}
</ref> The nominal trajectory suggests that Haumea is in a weak 7:12 orbital resonance with Neptune, which would make it a resonant trans-Neptunian object instead.<ref name="candidate">
{{cite journal
| author1 = Ragozzine, D.
| date = 2007
| title = Candidate Members and Age Estimate of the Family of Kuiper Belt Object 2003&nbsp;EL<sub>61</sub>
| journal = Astronomical Journal
| volume = 134
| issue = 6
| pages = 2160–2167
| doi = 10.1086/522334
| bibcode = 2007AJ....134.2160R
| arxiv = 0709.0328
| author2 = Brown, M. E.
}}
</ref> There are precovery images of Haumea dating back to March 22, 1955 from the Palomar Mountain Digitized Sky Survey.<ref name="Buie">{{cite web
 |author      = Marc W. Buie
 |date        = 2008-06-25
 |title       = Orbit Fit and Astrometric record for 136108
 |publisher   = Southwest Research Institute (Space Science Department)
 |url         = http://www.boulder.swri.edu/~buie/kbo/astrom/136108.html
 |accessdate  = 2008-10-02
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20110518005546/http://www.boulder.swri.edu/~buie/kbo/astrom/136108.html
 |archivedate = 2011-05-18
 |df          = }}</ref>

Haumea has an orbital period of 284 Earth years, a perihelion of 35&nbsp;AU, and an orbital inclination of 28°.<ref name="jpldata2014" /> It passed aphelion in early 1992,<ref name="Horizons">
{{cite web
 |title       = HORIZONS Web-Interface
 |publisher   = NASA Jet Propulsion Laboratory Solar System Dynamics
 |url         = http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=2003EL61
 |accessdate  = 2008-07-02
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20080718195959/http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=2003EL61
 |archivedate = 2008-07-18
 |df          = 
}}
</ref> and is currently more than 50&nbsp;AU from the Sun.<ref name="AstDysHaumea">
{{cite web
 |title       = AstDys (136108) Haumea Ephemerides
 |publisher   = Department of Mathematics, University of Pisa, Italy
 |url         = http://hamilton.dm.unipi.it/astdys/index.php?pc=1.1.3.0&n=Haumea
 |accessdate  = 2009-03-19
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20110629202435/http://hamilton.dm.unipi.it/astdys/index.php?pc=1.1.3.0&n=Haumea
 |archivedate = 2011-06-29
 |df          = }}</ref>

Haumea's orbit has a slightly greater orbital eccentricity than that of the other members of the Haumea family, its collisional family. This is thought to be due to Haumea's weak 7:12 orbital resonance with Neptune gradually modifying its initial orbit over the course of a billion years,<ref name="BrownBarkume2007">{{cite journal
| author1 = Brown, M. E.
| date = 2007
| title = A collisional family of icy objects in the Kuiper belt
| journal = Nature
| volume = 446
| issue = 7133
| pages = 294–296
| doi = 10.1038/nature05619
| pmid=17361177
| bibcode = 2007Natur.446..294B
| author2 = Barkume, K. M.
| author3 = Ragozzine, D.
| author4 = Schaller, L.}}</ref><ref name="largest">{{cite web
 |title       = The largest Kuiper belt objects
 |author      = Michael E. Brown
 |work        = CalTech
 |url         = http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf
 |accessdate  = 2008-09-19
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20081001170118/http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf
 |archivedate = 2008-10-01
 |df          = }}</ref> through the Kozai mechanism, or Kozai effect, which allows the exchange of an orbit's inclination for increased eccentricity.<ref name="BrownBarkume2007" /><ref name="Nesvorny2001">{{cite journal
| last = Nesvorný
| first = D
| author2=Roig, F.
| date = 2001
| title = Mean Motion Resonances in the Transneptunian Region Part II: The 1 : 2, 3 : 4, and Weaker Resonances
| journal = Icarus
| volume = 150
| issue = 1
| pages = 104–123
| bibcode = 2001Icar..150..104N
| doi = 10.1006/icar.2000.6568 }}</ref><ref name="Kuchner2002">
{{cite journal
| last = Kuchner | first = Marc J.
| last3 = Holman | first3 = Matthew
| date = 2002
| title = Long-Term Dynamics and the Orbital Inclinations of the Classical Kuiper Belt Objects
| journal = The Astronomical Journal
| volume = 124
| issue = 2
| pages = 1221–1230
| bibcode = 2002AJ....124.1221K
| doi = 10.1086/341643
| arxiv = astro-ph/0206260 }}</ref>

With a visual magnitude of 17.3,<ref name="AstDysHaumea" /> Haumea is the third-brightest object in the Kuiper belt after Pluto and Makemake, and easily observable with a large amateur telescope.<ref name="Rabinowitz2005" /> However, because the planets and most small Solar System bodies share a invariable plane, or common orbital alignment, from their formation in the protoplanetary, primordial disk, of the Solar System, most early surveys for distant objects focused on the projection on the sky of this common plane, called the ecliptic.<ref name="TrujilloBrown2003">
{{cite journal
| author = C. A. Trujillo
| author2 = M. E. Brown
| last-author-amp = yes
| title = The Caltech Wide Area Sky Survey
| pages = 92–99
| issue = 1–4
| volume = 112
| date = June 2003
| doi = 10.1023/B:MOON.0000031929.19729.a1
| journal = Earth, Moon, and Planets
| bibcode = 2003EM&P...92...99T
}}
</ref> As the region of sky close to the ecliptic became well explored, later sky surveys began looking for objects that had been dynamically excited into orbits with higher inclinations, as well as more distant objects, with slower mean motions across the sky.<ref name="Brown2004">
{{cite journal
| author1 = Brown, M. E.
| date = 2004
| title = Discovery of a candidate inner Oort cloud planetoid
| journal = The Astrophysical Journal
| volume = 617
| issue = 1
| pages = 645–649
| doi = 10.1086/422095
| bibcode = 2004ApJ...617..645B
| arxiv = astro-ph/0404456
| author2 = Trujillo, C.
| author3 = Rabinowitz, D. L.
}}
</ref><ref name="Schwamb2008">{{cite journal
| author1 = Schwamb, M. E.
| date = 2008
| title = Constraints on the distant population in the region of Sedna
| volume = 40
| pages = 465
| journal = American Astronomical Society, DPS Meeting #40, #38.07
| bibcode = 2008DPS....40.3807S
| author2 = Brown, M. E.
| author3 = Rabinowitz, D. L. }}</ref>

Haumea displays large fluctuations in brightness over a period of 3.9 hours, which can only be explained by a rotational period of this length.<ref name="AFP2009">
{{cite web
 |publisher=News Limited 
 |title=Astronomers get lock on diamond-shaped Haumea 
 |work=European Planetary Science Congress in Potsdam 
 |date=2009-09-16 
 |url=http://www.news.com.au/story/0,27574,26081101-23109,00.html 
 |accessdate=2009-09-16 
 |author=Agence France-Presse 
 |deadurl=yes 
|archiveurl=https://web.archive.org/web/20090923170519/http://www.news.com.au/story/0%2C27574%2C26081101-23109%2C00.html 
 |archivedate=2009-09-23 
 |df= 
}}
</ref> This is faster than any other known equilibrium body in the [[Solar System]], and indeed faster than any other known body larger than 100&nbsp;km in diameter.<ref name="Rabinowitz2005" /> While most rotating bodies in equilibrium are flattened into oblate spheroids, Haumea rotates so quickly that it is distorted into a triaxial ellipsoid. If Haumea were to rotate much more rapidly, it would distort itself into a dumbbell shape and split in two.<ref name="iau" /> This rapid rotation is thought to have been caused by the impact that created its satellites and collisional family.<ref name="BrownBarkume2007" />
Because Haumea has moons, the mass of the system can be calculated from their orbits using Kepler's third law. The result is {{nowrap|4.2{{e|21}} kg,}} 28% the mass of the Plutonian system and 6% that of the Moon. Nearly all of this mass is in Haumea.<ref name="RagozzineBrown2009">
{{cite journal
| author1 = Ragozzine, D.
| date = 2009
| title = Orbits and Masses of the Satellites of the Dwarf Planet Haumea = 2003 EL61
| journal = The Astronomical Journal
| arxiv = 0903.4213
| bibcode = 2009AJ....137.4766R
| doi = 10.1088/0004-6256/137/6/4766
| volume = 137
| issue = 6
| pages = 4766–4776
| author2 = Brown, M. E.
}}
</ref><ref name="Brown2005">
{{cite journal
 |author      = Brown, M. E.
 |date        = 2005
 |title       = Keck Observatory laser guide star adaptive optics discovery and characterization of a satellite to large Kuiper belt object 2003&nbsp;EL<sub>61</sub>
 |url         = http://www.gps.caltech.edu/%7Embrown/papers/ps/EL61.pdf
 |journal     = Astrophysical Journal Letters
 |volume      = 632
 |issue       = 1
 |pages       = L45
 |doi         = 10.1086/497641
 |bibcode     = 2005ApJ...632L..45B
 |last2       = Bouchez
 |first2      = A. H.
 |last3       = Rabinowitz
 |first3      = D.
 |last4       = Sari
 |first4      = R.
 |last5       = Trujillo
 |first5      = C. A.
 |last6       = Van Dam
 |first6      = M.
 |last7       = Campbell
 |first7      = R.
 |last8       = Chin
 |first8      = J.
 |last9       = Hartman
 |first9      = S.
 |last10      = Johansson
 |first10     = E.
 |last11      = Lafon
 |first11     = R.
 |last12      = Le Mignant
 |first12     = D.
 |last13      = Stomski
 |first13     = P.
 |last14      = Summers
 |first14     = D.
 |last15      = Wizinowich
 |first15     = P.
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20100610233232/http://www.gps.caltech.edu/%7Embrown/papers/ps/EL61.pdf
 |archivedate = 2010-06-10
 |df          = 
}}
</ref>

For most distant objects, the albedo is unknown, but Haumea is large and bright enough for its infrared, thermal emission to be measured, which has given an approximate value for its albedo and thus its size.<ref name="spitzer">
{{cite journal
| author1 = Stansberry, J.
| title = Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope
| journal = The Solar System Beyond Neptune
| pages = 161
| publisher = University of Arizona Press
| date = 2008
| arxiv = astro-ph/0702538
| bibcode = 2008ssbn.book..161S
| author2 = Grundy, W.
| author3 = Brown, M.
| author4 = Cruikshank, D.
| author5 = Spencer, J.
| author6 = Trilling, D.
| author7 = Margot, J-L. }}</ref>

The rigid body dynamics, specifically, rotational physics of deformable bodies predicts that over as little as a hundred days,<ref name="Rabinowitz2005" /> a body rotating as rapidly as Haumea will have been distorted into the hydrostatic equilibrium form of a triaxial ellipsoid. It is thought that most of the fluctuation in Haumea's brightness is caused not by local differences in albedo but by the alternation of the side view and end view as seen from Earth.<ref name="Rabinowitz2005" />

If Haumea were in hydrostatic equilibrium and had a low density like Pluto, with a thick mantle of volatiles, such as ice, over a small silicate, rocky core, its rapid rotation would have elongated it to a greater extent than the fluctuations in its brightness allow. Such considerations constrained its density to a range of 2.6–3.3&nbsp;g/cm<sup>3</sup>.<ref name="Lockwood2014">
{{cite journal
| author = Alexandra C. Lockwood
| author2 = Michael E. Brown
| author3 = John Stansberry
| date = 2014
| title = The size and shape of the oblong dwarf planet Haumea
| journal = Earth, Moon, and Planets
| arxiv = 1402.4456v1
| doi = 10.1007/s11038-014-9430-1
| volume = 111
| issue = 3–4
| pages = 127–137
| bibcode = 2014EM&P..111..127L }}</ref><ref name="Rabinowitz2005" />

In 2005, the Gemini Observatory and Keck Observatory telescopes obtained spectra of Haumea which showed strong crystalline water ice features similar to the surface of Pluto's moon Charon.<ref name="Trujillo 2006">
{{cite journal
| date = 2007
| title = The Surface of 2003&nbsp;EL<sub>61</sub> in the Near Infrared
| journal = The Astrophysical Journal
| volume = 655
| issue = 2
| pages = 1172–1178
| doi = 10.1086/509861
| arxiv = astro-ph/0601618
| bibcode = 2007ApJ...655.1172T
| name-list-format = vanc
| author1 = Chadwick A. Trujillo
| author2 = Michael E. Brown
| author3 = Kristina Barkume
| author4 = Emily Shaller
| author5 = David L. Rabinowitz }}</ref> This is peculiar, because crystalline ice forms at temperatures above 110&nbsp;K, whereas Haumea's surface temperature is below 50&nbsp;K, a temperature at which amorphous ice is formed.<ref name="Trujillo 2006" /> In addition, the structure of crystalline ice is unstable under the constant rain of cosmic rays and energetic particles from the Sun that strike trans-Neptunian objects.<ref name="Trujillo 2006" /> The timescale for the crystalline ice to revert to amorphous ice under this bombardment is on the order of ten million years,<ref name="Gemini-Charon ice machine">{{cite web
 |publisher   = Gemini Observatory
 |date        = 17 July 2007
 |title       = Charon: An ice machine in the ultimate deep freeze
 |url         = http://www.spaceflightnow.com/news/n0707/17charon/
 |accessdate  = 2007-07-18
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20110607020940/http://www.spaceflightnow.com/news/n0707/17charon/
 |archivedate = 7 June 2011
 |df          = }}</ref> yet trans-Neptunian objects have been in their present cold-temperature locations for timescales of billions of years.<ref name="largest" /> Radiation damage should also redden and darken the surface of trans-Neptunian objects where the common surface materials of organic molecular ices and tholin-like compounds are present, as is the case with Pluto. Therefore, the spectra and colour suggest Haumea and its family members have undergone recent resurfacing that produced fresh ice. However, no plausible resurfacing mechanism has been suggested.<ref name="Rabinowitz2008">{{cite journal
| author1 = Rabinowitz, D. L.
| title = The Youthful Appearance of the 2003 EL<sub>61</sub> Collisional Family
| date = 2008
| doi = 10.1088/0004-6256/136/4/1502
| journal = The Astronomical Journal
| volume = 136
| issue = 4
| pages = 1502–1509
| arxiv = 0804.2864
| bibcode = 2008AJ....136.1502R
| last2 = Schaefer
| first2 = Bradley E.
| last3 = Schaefer
| first3 = Martha
| last4 = Tourtellotte
| first4 = Suzanne W.}}</ref>

Haumea is as bright as snow, with an albedo in the range of 0.6–0.8, consistent with crystalline ice.<ref name="Rabinowitz2005">{{cite journal
| author = Rabinowitz, D. L.
| date = 2006
| title = Photometric Observations Constraining the Size, Shape, and Albedo of 2003&nbsp;EL<sub>61</sub>, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt
| journal = Astrophysical Journal
| volume = 639
| issue = 2
| pages = 1238–1251
| doi = 10.1086/499575
| bibcode = 2006ApJ...639.1238R
| arxiv = astro-ph/0509401
| last2 = Barkume
| first2 = Kristina
| last3 = Brown
| first3 = Michael E.
| last4 = Roe
| first4 = Henry
| last5 = Schwartz
| first5 = Michael
| last6 = Tourtellotte
| first6 = Suzanne
| last7 = Trujillo
| first7 = Chad}}</ref> Other large TNOs such as Eris appear to have albedos as high or higher.<ref name="Brown2006xsize">{{cite journal
 |author1     = Brown, M. E.
 |date        = 2006
 |title       = Direct measurement of the size of 2003 UB313 from the Hubble Space Telescope
 |url         = http://www.gps.caltech.edu/~mbrown/papers/ps/xsize.pdf
 |journal     = The Astrophysical Journal Letters
 |volume      = 643
 |issue       = 2
 |pages       = L61–L63
 |doi         = 10.1086/504843
 |bibcode     = 2006ApJ...643L..61B
 |arxiv       = astro-ph/0604245
 |last2       = Schaller
 |first2      = E. L.
 |last3       = Roe
 |first3      = H. G.
 |last4       = Rabinowitz
 |first4      = D. L.
 |last5       = Trujillo
 |first5      = C. A.
 |deadurl     = no
 |archiveurl  = https://web.archive.org/web/20080910103928/http://www.gps.caltech.edu/~mbrown/papers/ps/xsize.pdf
 |archivedate = 2008-09-10
 |df          = 
}}
</ref> Best-fit modeling of the surface spectra suggested that 66% to 80% of the Haumean surface appears to be pure crystalline water ice, with one contributor to the high albedo possibly hydrogen cyanide or phyllosilicate clays.<ref name="Trujillo 2006" /> Inorganic cyanide salts such as copper potassium cyanide may also be present.<ref name="Trujillo 2006" />

Visible and near infrared spectra suggest a homogeneous surface covered by an intimate 1:1 mixture of amorphous and crystalline ice, together with no more than 8% organics. The absence of ammonia hydrate excludes cryovolcanism and the observations confirm that the collisional event must have happened more than 100 million years ago, in agreement with the dynamic studies.<ref name="Pinilla-Alonso2009">
{{cite journal
| author1 = Pinilla-Alonso, N.
| date = 2009
| title = Study of the Surface of 2003 EL61, the largest carbon-depleted object in the trans-neptunian belt
| journal = Astronomy and Astrophysics
| volume = 496
| issue = 2
| pages =547–556
| arxiv = 0803.1080
| doi = 10.1051/0004-6361/200809733
| bibcode = 2009A&A...496..547P
| last2 = Brunetto
| first2 = R.
| last3 = Licandro
| first3 = J.
| last4 = Gil-Hutton
| first4 = R.
| last5 = Roush
| first5 = T. L.
| last6 = Strazzulla
| first6 = G.
}}
</ref> The absence of measurable methane in the spectra of Haumea is consistent with a warm collisional history that would have removed such volatiles,<ref name="Trujillo 2006" /> in contrast to Makemake.<ref name="Tegler07">{{cite journal
| author1 = Tegler, S. C.
| date = 2007
| title = Optical Spectroscopy of the Large Kuiper Belt Objects 136472 (2005 FY<sub>9</sub>) and 136108 (2003 EL<sub>61</sub>)
| doi = 10.1086/510134
| journal = The Astronomical Journal
| volume = 133
| issue = 2
| pages = 526–530
| arxiv = astro-ph/0611135
|bibcode = 2007AJ....133..526T | last2 = Grundy
| first2 = W. M.
| last3 = Romanishin
| first3 = W.
| last4 = Consolmagno
| first4 = G. J.
| last5 = Mogren
| first5 = K.
| last6 = Vilas
| first6 = F. }}</ref>
{{clear}}

==Interstellar comets==
[[Image:Oumuamua-solar system 2018.png|right|thumb|300px|This shows the hyperbolic path of extrasolar object ʻOumuamua, the first confirmed interstellar object, discovered in 2017. Credit: [[c:user:Tomruen|Tomruen]].{{tlx|free media}}]]
[[Image:96P 20070403 000500 HI1A.png|thumb|left|Comet Machholz 1 (96P/Machholz) is viewed by STEREO-A (April 2007). Credit: NASA.]] 
[[Image:Hyakutake Color.jpg|right|thumb|300px|Comet Hyakutake (C/1996 B2) might be an interstellar object captured by the Solar System. Credit: E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria.{{tlx|free media}}]]
An interstellar object is an astronomical object that is located in interstellar space including objects that are on an interstellar trajectory but are temporarily passing close to a star, such as certain asteroids and comets (including exocomets<ref name="Valtonen">{{ cite journal
| last = Valtonen| first = Mauri J.| author2 = Jia-Qing Zheng | author3 = Seppo Mikkola
| title = Origin of oort cloud comets in the interstellar space
| journal = Celestial Mechanics and Dynamical Astronomy
| volume = 54
| issue = 1–3
| pages = 37–48
| date = March 1992
| url = http://www.springerlink.com/content/g43v16167077453u/
| doi = 10.1007/BF00049542
| accessdate = 2008-12-30
|bibcode = 1992CeMDA..54...37V }}</ref><ref name="Francis">{{ cite journal
| last = Francis| first = Paul J.
| date  = 2005-12-20
| title = The Demographics of Long-Period Comets
| journal = The Astrophysical Journal
| volume = 635
| issue  = 2
| pages  = 1348–1361
| doi  = 10.1086/497684
| bibcode = 2005ApJ...635.1348F
| url = http://www.iop.org/EJ/article/0004-637X/635/2/1348/62880.web.pdf?request-id=035fe065-820f-4c15-b74e-1cb158b2a41d
| accessdate  = 2009-01-03
|arxiv = astro-ph/0509074 }}</ref>)

The image on the right shows `Oumuamua's hyperbolic trajectory across the full solar system, with annual markers, and planet positions on 1/1/2018.

"A newly discovered comet is screaming away from Earth, and based on its weird orbital trajectory might be the first comet ever observed to come from interstellar space. A sky-surveying telescope in Hawaii spotted the fast-moving object, now called C/2017 U1, on 18 October, after its closest approach to the sun. The following week, astronomers made 34 separate observations of the object and found it has a strange trajectory that doesn't appear to circle the sun."<ref name=Boyle>{{ cite journal
|author=Rebecca Boyle
|title=Glimpse of the first interstellar comet?
|journal=New scientist
|date=2017
|volume=
|issue=3150
|pages=15
|url=https://dialnet.unirioja.es/servlet/articulo?codigo=6438678
|arxiv=
|bibcode=
|doi=
|pmid=
|accessdate=16 February 2019 }}</ref>

ʻOumuamua showed no signs of a cometary coma despite its close approach to the Sun, but underwent non-gravitational acceleration which is seen in many icy comets,<ref name="Nature 27-6-2018">{{ cite journal |url=https://www.nature.com/articles/s41586-018-0254-4
|title=Non-gravitational acceleration in the trajectory of 1I/2017 U1 (ʻOumuamua)
|journal=Nature
|volume=559
|issue=7713
|pages=223–226
|year=2018
|doi=10.1038/s41586-018-0254-4
|pmid=29950718
|last1=Micheli |first1=M. |last2=Farnocchia |first2=D. |last3=Meech |first3=K.J. |last4=Buie |first4=M.W. |last5=Hainaut |first5=O.R. |last6=Prialnik |first6=D. |last7=Schörghofer |first7=N. |last8=Weaver |first8=H.A. |last9=Chodas |first9=P.W. |last10=Kleyna |first10=J.T. |last11=Weryk |first11=R. |last12=Wainscoat |first12=R.J. |last13=Ebeling |first13=H. |last14=Keane |first14=J.V. |last15=Chambers |first15=K.C. |last16=Koschny |first16=D. |last17=Petropoulos |first17=A.E. |display-authors=1 }}</ref><ref>{{ cite journal
|last=Królikowska|first=Małgorzata|last2=Dybczyński|first2=Piotr A.
|date=2013-10-01
|title=Near-parabolic comets observed in 2006-2010. The individualized approach to 1/a-determination and the new distribution of original and future orbits
|url=http://adsabs.harvard.edu/abs/2013MNRAS.435..440K
|journal=Monthly Notices of the Royal Astronomical Society
|volume=435
|pages=440–459
|doi=10.1093/mnras/stt1313
|issn=0035-8711
}}</ref> although other reasons have been suggested.<ref name="UT-230181031">{{ cite web
|last=Williams |first=Matt
|title=Could Oumuamua Be an Extra-Terrestrial Solar Sail?
|url=https://www.universetoday.com/140391/could-oumuamua-be-an-extra-terrestrial-solar-sail/
|date=2 November 2018
|work=Universe Today
|accessdate=2 November 2018 }}</ref><ref name="ARX-20181101">{{ cite arxiv
|last1=Bialy |first1=Shmuel |last2=Loeb |first2=Abraham
|title=Could Solar Radiation Explain ʻOumuamua's Peculiar Acceleration?
|date=26 October 2018
|eprint=1810.11490v4
|class=astro-ph.EP }}</ref><ref name="SA-201809287">{{ cite web
|last=Loeb |first=Abraham
|title=How to Search for Dead Cosmic Civilizations
|url=https://blogs.scientificamerican.com/observations/how-to-search-for-dead-cosmic-civilizations/
|date=26 September 2018
|work=Scientific American
|accessdate=26 September 2018 }}</ref>

The object could be a remnant of a disintegrated interstellar comet (or exocomet).<ref name="UT-20190201">{{ cite web
|last=Williams |first=Matt
|title=Oumuamua Could be the Debris Cloud of a Disintegrated Interstellar Comet
|url=https://www.universetoday.com/141398/oumuamua-could-be-the-debris-cloud-of-a-disintegrated-interstellar-comet/#more-141398
|date=1 February 2019
|work=Universe Today
|accessdate=2 February 2019 }}</ref><ref name="ARX-20190201">{{ cite journal
|last=Sekanina |first=Zdenek
|title=1I/‘Oumuamua As Debris Of Dwarf Interstellar Comet That Disintegrated Before Perihelion
|url=https://arxiv.org/pdf/1901.08704.pdf
|date=31 January 2019
|journal=arXiv
|arxiv=1901.08704v3
|accessdate=2 February 2019 }}</ref>

It is possible for objects orbiting a star to be ejected due to interaction with a third massive body, such a process was initiated in early 1980s when C/1980 E1, initially gravitationally bound to the Sun, passed near Jupiter and was accelerated sufficiently to reach escape velocity from the Solar System, changing its orbit from elliptical to hyperbolic and making it the most eccentric known object at the time, with an eccentricity of 1.057.<ref name="jpldata1986">{{ cite web
  |type=1986-12-02 last obs
  |title=JPL Small-Body Database Browser: C/1980 E1 (Bowell)
  |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=1980%20E1
  |accessdate=2010-01-08}}</ref> It is headed for interstellar space.

Asteroid (514107) 2015 BZ509 may be a former interstellar object, captured some 4.5 billion years ago, as evidenced by its co-orbital motion with Jupiter and its retrograde orbit around the Sun.<ref>{{ cite web
|url=http://www.sciencemag.org/news/2018/05/asteroid-came-another-solar-system-and-it-s-here-stay
|title=This asteroid came from another solar system—and it’s here to stay
|publisher=Science }}</ref>

An interstellar comet can probably, on rare occasions, be captured into a heliocentric orbit while passing through the [[Solar System]]. Computer simulations show that [[Jupiter]] is the only planet massive enough to capture one, and that this can be expected to occur once every sixty million years.<ref name="Torbett">{{ cite journal
| last = Torbett| first = M. V.
| title = Capture of 20 km/s approach velocity interstellar comets by three-body interactions in the planetary system
| journal = Astronomical Journal
| volume = 92
| pages = 171–175
| date = July 1986
| bibcode = 1986AJ.....92..171T
| doi = 10.1086/114148 }}</ref> Comets Machholz 1 and Comet Hyakutake C/1996 B2 are possible examples of such comets, as they have atypical chemical makeups for comets in the Solar System.<ref name="MacRobert">{{ cite news
| last = MacRobert| first = Alan
| title = A Very Oddball Comet
| publisher = Sky & Telescope
| date = 2008-12-02
| url = http://www.skyandtelescope.com/news/35379224.html
| accessdate = 2010-03-26 }}</ref><ref name="science">{{ cite journal
| last=Mumma | first=M.J. | author2 = Disanti, M.A. | author3 = dello Russo, N. | author4 = Fomenkova, M. | author5 = Magee-Sauer, K. | author6 = Kaminski, C.D. | author7 = D.X. Xie
| title=Detection of Abundant Ethane and Methane, Along with Carbon Monoxide and Water, in Comet C/1996 B2 Hyakutake: Evidence for Interstellar Origin
| journal=Science
| date=1996
| volume=272
| pages=1310–1314
| bibcode = 1996Sci...272.1310M
| doi=10.1126/science.272.5266.1310
| pmid=8650540
| issue=5266 }}</ref>

Current models of Oort cloud formation predict that more comets are ejected into interstellar space than are retained in the Oort cloud, with estimates varying from 3 to 100 times as many.<ref name=Francis/> Other simulations suggest that 90–99% of comets are ejected.<ref name="Choi">{{ cite web
| last = Choi | first = Charles Q.
| title = The Enduring Mysteries of Comets
| publisher = Space.com
| url = http://www.space.com/scienceastronomy/071224-mm-comet-mysteries.html
| date = 2007-12-24
| accessdate = 2008-12-30 }}</ref> There is no reason to believe comets formed in other star systems would not be similarly scattered.<ref name=Valtonen />

A more recent estimate, following the detection of 'Oumuamua, predicts that "The steady-state population of similar, ~100 m scale interstellar objects inside the orbit of Neptune is ~1{{e|4}}, each with a residence time of ~10 years."<ref name="Jewitt2017">{{ cite journal
|doi=10.3847/2041-8213/aa9b2f
|title=Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes
|journal=The Astrophysical Journal
|volume=850
|issue=2
|pages=L36
|year=2017
|last1=Jewitt|first1=David|last2=Luu|first2=Jane|last3=Rajagopal|first3=Jayadev|last4=Kotulla|first4=Ralf|last5=Ridgway|first5=Susan|last6=Liu|first6=Wilson|last7=Augusteijn|first7=Thomas
|bibcode=2017ApJ...850L..36J
|arxiv=1711.05687 }}</ref>

There should be hundreds of 'Oumuamua-size interstellar objects in the Solar System, based on calculated orbital characteristics, with known examples: 2011 SP25, 2017 RR2, 2017 SV13, and 2018 TL6.<ref name="MNRAS-20181129">{{ cite journal
|last1=Siraj |first1=Amir |last2=Loeb |first2=Abraham
|title=Identifying Interstellar Objects Trapped in the Solar System through Their Orbital Parameters
|url=https://arxiv.org/pdf/1811.09632.pdf
|date=29 November 2018
|journal=Monthly Notices of the Royal Astronomical Society
|volume=000
|pages=1-5
|accessdate=1 December 2018 }}</ref> These are all orbiting the sun, but with unusual orbits, and are assumed to have been trapped at some occasion.
{{clear}}

==Acknowledgements==

The content on this page was first contributed by: Henry A. Hoff.

Initial content for this page in some instances came from [http://www.wikiversity.org Wikiversity].

==See also==
{{div col|colwidth=12em}}
* [[Radiation astronomy/Asteroids|Asteroid astronomy]]
* [[Radiation astronomy/Comets|Cometary astronomy]]
* [[Radiation astronomy/Kuiper belts|Kuiper belt astronomy]]
* [[Radiation astronomy/Oort clouds|Oort cloud astronomy]]
{{Div col end}}

==References==
{{reflist|2}}

==External links==
* [http://simbad.u-strasbg.fr/simbad/ Simbad at Strasbourg]

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