Editing Solar System (section)

== Trans-Neptunian region ==
Beyond the orbit of Neptune lies the area of the "[[trans-Neptunian object|trans-Neptunian region]]", with the doughnut-shaped Kuiper belt, home of Pluto and several other dwarf planets, and an overlapping disc of scattered objects, which is [[Orbital inclination|tilted toward the plane]] of the Solar System and reaches much further out than the Kuiper belt. The entire region is still [[Timeline of Solar System exploration|largely unexplored]]. It appears to consist overwhelmingly of many thousands of small worlds—the largest having a diameter only a fifth that of Earth and a mass far smaller than that of the Moon—composed mainly of rock and ice. This region is sometimes described as the "third zone of the Solar System", enclosing the inner and the outer Solar System.<ref>{{Cite web |last=Stern |first=Alan |author-link=Alan Stern |date=February 2015 |title=Journey to the Solar System's Third Zone |url=https://www.americanscientist.org/article/journey-to-the-solar-systems-third-zone |url-status=live |archive-url=https://web.archive.org/web/20181026222414/https://www.americanscientist.org/article/journey-to-the-solar-systems-third-zone |archive-date=26 October 2018 |access-date=26 October 2018 |website=American Scientist}}</ref>

=== Kuiper belt ===
{{Main|Kuiper belt}}
[[File:Kuiper belt plot objects of outer solar system.png|right|thumb|Plot of objects around the [[Kuiper belt]] and other asteroid populations. J, S, U and N denotes Jupiter, Saturn, Uranus and Neptune.]]

[[File:TheKuiperBelt_classes-en.svg|thumb|Orbit classification of Kuiper belt objects. Some clusters that is subjected to [[orbital resonance]] are marked.]]
The Kuiper belt is a great ring of debris similar to the asteroid belt, but consisting mainly of objects composed primarily of ice.<ref name="physical">{{Cite book |last=Tegler |first=Stephen C. |url=https://archive.org/details/encyclopediasola00mcfa_702 |title=Encyclopedia of the Solar System |date=2007 |isbn=978-0120885893 |editor-last=Lucy-Ann McFadden |page=[https://archive.org/details/encyclopediasola00mcfa_702/page/n622 605]–620 |chapter=Kuiper Belt Objects: Physical Studies |display-editors=etal |url-access=limited}}</ref> It extends between 30 and 50&nbsp;AU from the Sun. It is composed mainly of small Solar System bodies, although the largest few are probably large enough to be dwarf planets.<ref name="Grundy2019">{{Cite journal |last1=Grundy |first1=W. M. |last2=Noll |first2=K. S. |last3=Buie |first3=M. W. |last4=Benecchi |first4=S. D. |last5=Ragozzine |first5=D. |last6=Roe |first6=H. G. |date=December 2018 |title=The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ({{Mp|(229762) 2007 UK|126}}) |url=http://www2.lowell.edu/~grundy/abstracts/2019.G-G.html |volume=334 |pages=30–38 |doi=10.1016/j.icarus.2018.12.037 |s2cid=126574999 |archive-url=https://web.archive.org/web/20190407045339/http://www2.lowell.edu/~grundy/abstracts/preprints/2019.G-G.pdf |archive-date=7 April 2019 |journal=Icarus|bibcode=2019Icar..334...30G }}</ref> There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than {{Convert|50|km|abbr=on|sigfig=1}}, but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of Earth.<ref name="Delsanti-Beyond_The_Planets">{{Cite web |last1=Delsanti |first1=Audrey |last2=Jewitt |first2=David |date=2006 |title=The Solar System Beyond The Planets |url=http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf |url-status=dead |archive-url=https://web.archive.org/web/20070129151907/http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf |archive-date=29 January 2007 |access-date=3 January 2007 |website=Institute for Astronomy, University of Hawaii}}</ref> Many Kuiper belt objects have satellites,<ref>{{Cite journal |last1=Brown |first1=M.E. |author-link=Michael E. Brown |last2=Van Dam |first2=M.A. |last3=Bouchez |first3=A.H. |last4=Le Mignant |first4=D. |last5=Campbell |first5=R.D. |last6=Chin |first6=J.C.Y. |last7=Conrad |first7=A. |last8=Hartman |first8=S.K. |last9=Johansson |first9=E.M. |last10=Lafon |first10=R.E. |last11=Rabinowitz |first11=D.L. Rabinowitz |last12=Stomski |first12=P.J. Jr. |last13=Summers |first13=D.M. |last14=Trujillo |first14=C.A. |last15=Wizinowich |first15=P.L. |year=2006 |title=Satellites of the Largest Kuiper Belt Objects |url=http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf |url-status=live |journal=[[The Astrophysical Journal]] |volume=639 |issue=1 |pages=L43–L46 |arxiv=astro-ph/0510029 |bibcode=2006ApJ...639L..43B |doi=10.1086/501524 |s2cid=2578831 |archive-url=https://web.archive.org/web/20180928185647/http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf |archive-date=28 September 2018 |access-date=19 October 2011 |ref={{SfnRef|Brown Van Dam et al.|2006}}}}</ref> and most have orbits that are substantially inclined (~10°) to the plane of the ecliptic.<ref name="trojan">{{Cite journal |last1=Chiang |first1=E.I. |last2=Jordan |first2=A.B. |last3=Millis |first3=R.L. |last4=Buie |first4=M.W. |last5=Wasserman |first5=L.H. |last6=Elliot |first6=J.L. |last7=Kern |first7=S.D. |last8=Trilling |first8=D.E. |last9=Meech |first9=K.J. |last10=Wagner |first10=R.M. |display-authors=9 |date=2003 |title=Resonance Occupation in the Kuiper Belt: Case Examples of the 5:2 and Trojan Resonances |url=http://www.boulder.swri.edu/~buie/biblio/pub047.pdf |url-status=live |journal=[[The Astronomical Journal]] |volume=126 |issue=1 |pages=430–443 |arxiv=astro-ph/0301458 |bibcode=2003AJ....126..430C |doi=10.1086/375207 |s2cid=54079935 |archive-url=https://web.archive.org/web/20160315175243/http://www.boulder.swri.edu//~buie/biblio/pub047.pdf |archive-date=15 March 2016 |access-date=15 August 2009}}</ref>

The Kuiper belt can be roughly divided into the "[[Classical Kuiper belt object|classical]]" belt and the [[resonant trans-Neptunian object]]s.<ref name="physical" /> The latter have orbits whose periods are in a simple ratio to that of Neptune: for example, going around the Sun twice for every three times that Neptune does, or once for every two. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4 to 47.7&nbsp;AU.<ref>{{Cite journal |last1=Buie |first1=M. W. |last2=Millis |first2=R. L. |last3=Wasserman |first3=L. H. |last4=Elliot |first4=J. L. |last5=Kern |first5=S. D. |last6=Clancy |first6=K. B. |last7=Chiang |first7=E. I. |last8=Jordan |first8=A. B. |last9=Meech |first9=K. J. |last10=Wagner |first10=R. M. |last11=Trilling |first11=D. E. |date=2005 |title=Procedures, Resources and Selected Results of the Deep Ecliptic Survey |journal=[[Earth, Moon, and Planets]] |volume=92 |issue=1 |pages=113–124 |arxiv=astro-ph/0309251 |bibcode=2003EM&P...92..113B |doi=10.1023/B:MOON.0000031930.13823.be |s2cid=14820512}}</ref> Members of the classical Kuiper belt are sometimes called "cubewanos", after the first of their kind to be discovered, originally designated [[15760 Albion|1992 ''QB<sub>1</sub>'']], (and has since been named Albion); they are still in near primordial, low-eccentricity orbits.<ref>{{Cite journal |last1=Dotto |first1=E. |last2=Barucci |first2=M. A. |last3=Fulchignoni |first3=M. |date=1 January 2003 |title=Beyond Neptune, the new frontier of the Solar System |url=http://sait.oat.ts.astro.it/MSAIS/3/PDF/20.pdf |url-status=live |journal=Memorie della Societa Astronomica Italiana Supplementi |volume=3 |page=20 |bibcode=2003MSAIS...3...20D |issn=0037-8720 |archive-url=https://web.archive.org/web/20140825122005/http://sait.oat.ts.astro.it/MSAIS/3/PDF/20.pdf |archive-date=25 August 2014 |access-date=26 December 2006}}</ref>

There is strong consensus among astronomers that five members of the Kuiper belt are {{Visible anchor|Others|text=dwarf planets}}.<ref name="Grundy2019" /><ref name="JWST">{{cite journal |arxiv=2309.15230 |first1=J. P. |last1=Emery |first2=I. |last2=Wong |author-link= |title=A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar from JWST Spectroscopy |date=2024 |first3=R. |last3=Brunetto |first4=J. C. |last4=Cook |first5=N. |last5=Pinilla-Alonso |first6=J. A. |last6=Stansberry |first7=B. J. |last7=Holler |first8=W. M. |last8=Grundy |first9=S. |last9=Protopapa |first10=A. C. |last10=Souza-Feliciano |first11=E. |last11=Fernández-Valenzuela |first12=J. I. |last12=Lunine |first13=D. C. |last13=Hines|journal=Icarus |volume=414 |doi=10.1016/j.icarus.2024.116017 |bibcode=2024Icar..41416017E }}</ref> Many dwarf planet candidates are being considered, pending further data for verification.<ref name="Tancredi2008">{{Cite journal |last1=Tancredi |first1=G. |last2=Favre |first2=S. A. |year=2008 |title=Which are the dwarfs in the Solar System? |journal=Icarus |volume=195 |issue=2 |pages=851–862 |bibcode=2008Icar..195..851T |doi=10.1016/j.icarus.2007.12.020}}</ref>
* {{Visible anchor|Pluto and Charon|text=[[Pluto]]}} (29.7–49.3&nbsp;AU) is the largest known object in the Kuiper belt. Pluto has a relatively eccentric orbit, inclined 17 degrees to the [[ecliptic plane]]. Pluto has a [[Orbital resonance|2:3 resonance]] with Neptune, meaning that Pluto orbits twice around the Sun for every three Neptunian orbits. Kuiper belt objects whose orbits share this resonance are called [[plutino]]s.<ref name="Fajans_et_al_2001">{{Cite journal |last1=Fajans |first1=J. |last2=Frièdland |first2=L. |date=October 2001 |title=Autoresonant (nonstationary) excitation of pendulums, Plutinos, plasmas, and other nonlinear oscillators |url=http://ist-socrates.berkeley.edu/~fajans/pub/pdffiles/AutoPendAJP.pdf |url-status=dead |journal=[[American Journal of Physics]] |volume=69 |issue=10 |pages=1096–1102 |bibcode=2001AmJPh..69.1096F |doi=10.1119/1.1389278 |archive-url=https://web.archive.org/web/20110607210435/http://ist-socrates.berkeley.edu/~fajans/pub/pdffiles/AutoPendAJP.pdf |archive-date=7 June 2011 |access-date=26 December 2006}}</ref> [[Moons of Pluto|Pluto has five moons]]: Charon, [[Styx (moon)|Styx]], [[Nix (moon)|Nix]], [[Kerberos (moon)|Kerberos]], and [[Hydra (moon)|Hydra]].<ref>{{Cite web |date=6 August 2021 |title=In Depth: Pluto |url=https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth |url-status=live |archive-url=https://web.archive.org/web/20220331112026/https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth |archive-date=31 March 2022 |access-date=31 March 2022 |website=NASA Science: Solar System Exploration}}</ref>
** [[Charon (moon)|Charon]], the largest of Pluto's moons, is sometimes described as part of a [[binary system (astronomy)|binary system]] with Pluto, as the two bodies orbit a [[barycenter]] of gravity above their surfaces (i.e. they appear to "orbit each other").
* {{Dp|Orcus}} (30.3–48.1&nbsp;AU), is in the same 2:3 orbital resonance with Neptune as Pluto, and is the largest such object after Pluto itself.<ref name="brownlargest" /> Its eccentricity and inclination are similar to Pluto's, but its perihelion lies about 120° from that of Pluto. Thus, the [[Phase (waves)#Phase difference|phase]] of Orcus's orbit is opposite to Pluto's: Orcus is at aphelion (most recently in 2019) around when Pluto is at perihelion (most recently in 1989) and vice versa.<ref name="MPC2004-D15">{{Cite web |date=20 February 2004 |title=MPEC 2004-D15 : 2004 DW |url=http://www.minorplanetcenter.net/mpec/K04/K04D15.html |url-status=live |archive-url=https://web.archive.org/web/20160303232947/http://www.minorplanetcenter.net/mpec/K04/K04D15.html |archive-date=3 March 2016 |access-date=5 July 2011 |publisher=Minor Planet Center}}</ref> For this reason, it has been called the ''anti-Pluto''.<ref name="MBP">{{Cite web |last=Michael E. Brown |author-link=Michael E. Brown |date=23 March 2009 |title=S/2005 (90482) 1 needs your help |url=http://www.mikebrownsplanets.com/2009/03/s1-90482-2005-needs-your-help.html |url-status=live |archive-url=https://web.archive.org/web/20090328012339/http://www.mikebrownsplanets.com/2009/03/s1-90482-2005-needs-your-help.html |archive-date=28 March 2009 |access-date=25 March 2009 |publisher=Mike Brown's Planets (blog)}}</ref><ref>{{Cite book |last=Moltenbrey |first=Michael |url=https://www.worldcat.org/oclc/926914921 |title=Dawn of Small Worlds: Dwarf planets, asteroids, comets |date=2016 |publisher=Springer |isbn=978-3-319-23003-0 |location=Cham |page=171 |oclc=926914921 |access-date=9 April 2022 |archive-url=https://web.archive.org/web/20220420161222/https://www.worldcat.org/title/dawn-of-small-worlds-dwarf-planets-asteroids-comets/oclc/926914921 |archive-date=20 April 2022 |url-status=live}}</ref> It has one known moon, [[Vanth (moon)|Vanth]].<ref name="IAUC8812">{{Cite web |last=Green |first=Daniel W. E. |date=22 February 2007 |title=IAUC 8812: Sats OF 2003 AZ_84, (50000), (55637), (90482) |url=http://www.cbat.eps.harvard.edu/iauc/08800/08812.html |url-status=live |archive-url=https://web.archive.org/web/20120314060043/http://cbat.eps.harvard.edu/iauc/08800/08812.html |archive-date=14 March 2012 |access-date=4 July 2011 |publisher=International Astronomical Union Circular}}</ref>
* [[Haumea]] (34.6–51.6&nbsp;AU) was discovered in 2005.<ref>{{Cite web |date=17 September 2008 |title=IAU names fifth dwarf planet Haumea |url=https://www.iau.org/news/pressreleases/detail/iau0807 |url-status=live |archive-url=https://web.archive.org/web/20140425065601/http://iau.org/public_press/news/detail/iau0807 |archive-date=25 April 2014 |access-date=9 April 2022 |website=International Astronomical Union}}</ref> It is in a temporary 7:12 orbital resonance with Neptune.<ref name="brownlargest">{{Cite book |last=Brown |first=Mike |title=The Solar System Beyond Neptune |publisher=University of Arizona Press |year=2008 |isbn=978-0-816-52755-7 |editor-last=Barucci |editor-first=M. Antonietta |pages=335–344 |chapter=The largest Kuiper belt objects |oclc=1063456240 |author-link=Mike Brown (astronomer) |access-date=9 April 2022 |chapter-url=http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf |archive-url=https://web.archive.org/web/20121113114533/http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf |archive-date=13 November 2012 |url-status=live}}</ref> Haumea possesses a ring system, two known moons named [[Hiʻiaka (moon)|Hiʻiaka]] and [[Namaka (moon)|Namaka]], and rotates so quickly (once every 3.9 hours) that it is stretched into an [[ellipsoid]]. It is part of a [[collisional family]] of Kuiper belt objects that share similar orbits, which suggests a giant impact on Haumea ejected fragments into space billions of years ago.<ref name="Noviello2022">{{Cite journal |last1=Noviello |first1=Jessica L. |last2=Desch |first2=Stephen J. |last3=Neveu |first3=Marc |last4=Proudfoot |first4=Benjamin C. N. |last5=Sonnett |first5=Sarah |date=September 2022 |title=Let It Go: Geophysically Driven Ejection of the Haumea Family Members |journal=The Planetary Science Journal |volume=3 |issue=9 |page=19 |bibcode=2022PSJ.....3..225N |doi=10.3847/PSJ/ac8e03 |s2cid=252620869 |id=225 |doi-access=free}}</ref>
* [[Makemake]] (38.1–52.8&nbsp;AU), although smaller than Pluto, is the largest known object in the ''classical'' Kuiper belt (that is, a Kuiper belt object not in a confirmed resonance with Neptune). Makemake is the brightest object in the Kuiper belt after Pluto. Discovered in 2005, it was officially named in 2009.<ref>{{Cite web |date=19 July 2009 |title=Fourth dwarf planet named Makemake |url=https://www.iau.org/news/pressreleases/detail/iau0806 |url-status=live |archive-url=https://web.archive.org/web/20170730222925/https://www.iau.org/news/pressreleases/detail/iau0806 |archive-date=30 July 2017 |access-date=9 April 2022 |website=International Astronomical Union}}</ref> Its orbit is far more inclined than Pluto's, at 29°.<ref name="Buie136472">{{Cite web |last=Buie |first=Marc W. |author-link=Marc W. Buie |date=5 April 2008 |title=Orbit Fit and Astrometric record for 136472 |url=http://www.boulder.swri.edu/~buie/kbo/astrom/136472.html |url-status=live |archive-url=https://web.archive.org/web/20200527191044/https://www.boulder.swri.edu/~buie/kbo/astrom/136472.html |archive-date=27 May 2020 |access-date=15 July 2012 |publisher=SwRI (Space Science Department)}}</ref> It has one known moon, [[S/2015 (136472) 1]].<ref name="ParkerA2016">{{Cite journal |last1=Parker |first1=A. H. |last2=Buie |first2=M. W. |last3=Grundy |first3=W. M. |last4=Noll |first4=K. S. |date=25 April 2016 |title=Discovery of a Makemakean Moon |journal=[[The Astrophysical Journal]] |volume=825 |issue=1 |page=L9 |arxiv=1604.07461 |bibcode=2016ApJ...825L...9P |doi=10.3847/2041-8205/825/1/L9 |s2cid=119270442 |doi-access=free}}</ref>
* {{Dp|Quaoar}} (41.9–45.5&nbsp;AU) is the second-largest known object in the classical Kuiper belt, after Makemake. Its orbit is significantly less eccentric and inclined than those of Makemake or Haumea.<ref name="brownlargest" /> It possesses a ring system and one known moon, [[Weywot (moon)|Weywot]].<ref name="Morgado2023">{{Cite Q|Q116754015|display-authors=1}}</ref>

=== Scattered disc ===
{{Main|Scattered disc}}

[[File:TheKuiperBelt Projections 100AU Classical SDO.svg|thumb|The orbital eccentricities and inclinations of the scattered disc population compared to the classical and resonant Kuiper belt objects]]
The scattered disc, which overlaps the Kuiper belt but extends out to near 500&nbsp;AU, is thought to be the source of short-period comets. Scattered-disc objects are believed to have been perturbed into erratic orbits by the gravitational influence of [[Formation and evolution of the Solar System#Planetary migration|Neptune's early outward migration]]. Most scattered disc objects have perihelia within the Kuiper belt but aphelia far beyond it (some more than 150&nbsp;AU from the Sun). SDOs' orbits can be inclined up to 46.8° from the ecliptic plane.<ref>{{Cite book |last1=Gomes |first1=R. S. |url=https://www.lpi.usra.edu/books/ssbn2008/7003.pdf |title=The Solar System Beyond Neptune |last2=Fernández |first2=J. A. |last3=Gallardo |first3=T. |last4=Brunini |first4=A. |date=2008 |publisher=University of Arizona Press |isbn=978-0816527557 |pages=259–273 |chapter=The Scattered Disk: Origins, Dynamics, and End States |access-date=12 May 2022 |archive-url=https://web.archive.org/web/20220121172507/https://www.lpi.usra.edu/books/ssbn2008/7003.pdf |archive-date=21 January 2022 |url-status=live}}</ref> Some astronomers consider the scattered disc to be merely another region of the Kuiper belt and describe scattered-disc objects as "scattered Kuiper belt objects".<ref>{{Cite web |last=Jewitt |first=David |date=2005 |title=The 1,000 km Scale KBOs |url=http://www2.ess.ucla.edu/~jewitt/kb/big_kbo.html |url-status=live |archive-url=https://web.archive.org/web/20140609134900/http://www2.ess.ucla.edu/~jewitt/kb/big_kbo.html |archive-date=9 June 2014 |access-date=16 July 2006 |website=University of Hawaii}}</ref> Some astronomers classify centaurs as inward-scattered Kuiper belt objects along with the outward-scattered residents of the scattered disc.<ref>{{Cite web |title=List of Centaurs and Scattered-Disk Objects |url=http://www.minorplanetcenter.org/iau/lists/Centaurs.html |url-status=live |archive-url=https://web.archive.org/web/20170629210646/http://www.minorplanetcenter.org/iau/lists/Centaurs.html |archive-date=29 June 2017 |access-date=2 April 2007 |website=IAU: Minor Planet Center}}</ref>

Currently, there is strong consensus among astronomers that two of the bodies in the scattered disc are {{Visible anchor|Gonggong and Eris|text=dwarf planets}}:
* {{Dp|Eris}} (38.3–97.5&nbsp;AU) is the largest known scattered disc object and the most massive known dwarf planet. Eris's discovery contributed to a debate about the definition of a planet because it is 25% more massive than Pluto<ref name="Brown Schaller 2007">{{Cite journal |last1=Brown |first1=Michael E. |author-link=Michael E. Brown |last2=Schaller |first2=Emily L. |date=15 June 2007 |title=The Mass of Dwarf Planet Eris |journal=Science |volume=316 |issue=5831 |page=1585 |bibcode=2007Sci...316.1585B |doi=10.1126/science.1139415 |pmid=17569855 |s2cid=21468196|url=https://resolver.caltech.edu/CaltechAUTHORS:20121001-135149660 }}</ref> and about the same diameter. It has one known moon, [[Dysnomia (moon)|Dysnomia]]. Like Pluto, its orbit is highly eccentric, with a perihelion of 38.2&nbsp;AU (roughly Pluto's distance from the Sun) and an aphelion of 97.6 AU, and steeply inclined to the ecliptic plane at an angle of 44°.<ref>{{Cite journal |last1=Dumas |first1=C. |last2=Merlin |first2=F. |last3=Barucci |first3=M. A. |last4=de Bergh |first4=C. |last5=Hainault |first5=O. |last6=Guilbert |first6=A. |last7=Vernazza |first7=P. |last8=Doressoundiram |first8=A. |date=August 2007 |title=Surface composition of the largest dwarf planet 136199 Eris (2003 UB{313}) |journal=Astronomy and Astrophysics |volume=471 |issue=1 |pages=331–334 |bibcode=2007A&A...471..331D |doi=10.1051/0004-6361:20066665 |doi-access=free}}</ref>
* {{Dp|Gonggong}} (33.8–101.2&nbsp;AU) is a dwarf planet in a comparable orbit to Eris, except that it is in a 3:10 resonance with Neptune.<ref name="jpldata" group="D">{{Cite web |date=10 April 2017 |title=JPL Small-Body Database Browser: 225088 Gonggong (2007 OR10) |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2225088 |url-status=live |archive-url=https://web.archive.org/web/20200610013703/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2225088 |archive-date=10 June 2020 |access-date=20 February 2020 |publisher=[[Jet Propulsion Laboratory]] |type=20 September 2015 last obs.}}</ref> It has one known moon, [[Xiangliu (moon)|Xiangliu]].<ref name="Kissetal2017">{{Cite journal |last1=Kiss |first1=Csaba |last2=Marton |first2=Gábor |last3=Farkas-Takács |first3=Anikó |last4=Stansberry |first4=John |last5=Müller |first5=Thomas |last6=Vinkó |first6=József |last7=Balog |first7=Zoltán |last8=Ortiz |first8=Jose-Luis |last9=Pál |first9=András |date=16 March 2017 |title=Discovery of a Satellite of the Large Trans-Neptunian Object (225088) 2007 OR<sub>10</sub> |journal=[[The Astrophysical Journal Letters]] |volume=838 |page=5 |arxiv=1703.01407 |bibcode=2017ApJ...838L...1K |doi=10.3847/2041-8213/aa6484 |s2cid=46766640 |id=L1 |doi-access=free |number=1}}</ref>

=== Extreme trans-Neptunian objects<span class="anchor" id="Detached objects"></span>===
{{Main|Extreme trans-Neptunian object}}
[[File:Distant object orbits + Planet Nine.png|thumb|upright=1.3|The current orbits of [[90377 Sedna|Sedna]], [[2012 VP113]], [[541132 Leleākūhonua|Leleākūhonua]] (pink), and other very [[ETNO|distant objects]] (red, brown and cyan) along with the predicted orbit of the hypothetical [[Planet Nine]] (dark blue)]]

Some objects in the Solar System have a very large orbit, and therefore are much less affected by the known giant planets than other minor planet populations. These bodies are called extreme trans-Neptunian objects, or ETNOs for short.<ref name="Sheppard-2018">{{cite journal |last1=Sheppard |first1=Scott S. |last2=Trujillo |first2=Chadwick A. |last3=Tholen |first3=David J. |last4=Kaib |first4=Nathan |year=2019 |title=A New High Perihelion Trans-Plutonian Inner Oort Cloud Object: 2015 TG387 |journal=The Astronomical Journal |volume=157 |issue=4 |page=139 |arxiv=1810.00013 |bibcode=2019AJ....157..139S |doi=10.3847/1538-3881/ab0895 |s2cid=119071596 |doi-access=free}}</ref> Generally, ETNOs' [[semi-major axis|semi-major axes]] are at least 150–250&nbsp;AU wide.<ref name="Sheppard-2018" /><ref name="Caju_outlier">{{cite journal |last1=de la Fuente Marcos |first1=Carlos |last2=de la Fuente Marcos |first2=Raúl |date=12 September 2018 |title=A Fruit of a Different Kind: 2015 BP<sub>519</sub> as an Outlier among the Extreme Trans-Neptunian Objects |journal=[[Research Notes of the AAS]] |volume=2 |issue=3 |pages=167 |arxiv=1809.02571 |bibcode=2018RNAAS...2..167D |doi=10.3847/2515-5172/aadfec |s2cid=119433944 |doi-access=free}}</ref> For example, [[541132 Leleākūhonua]] orbits the Sun once every ~32,000&nbsp;years, with a distance of 65–2000&nbsp;AU from the Sun.<ref name="jpldata2" group="D">{{cite web |title=JPL Small-Body Database Browser: (2015 TG387) |url=https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3830896 |access-date=13 December 2018 |publisher=[[Jet Propulsion Laboratory]] |type=2018-10-17 last obs. |archive-date=14 April 2020 |archive-url=https://web.archive.org/web/20200414180200/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3830896 |url-status=live }}</ref>

This population is divided into three subgroups by astronomers. The [[Scattered disc object|scattered]] ETNOs have [[perihelia]] around 38–45&nbsp;AU and an exceptionally high [[Orbital eccentricity|eccentricity]] of more than 0.85. As with the regular scattered disc objects, they were likely formed as result of [[Planetary migration#Gravitational scattering|gravitational scattering]] by Neptune and still interact with the giant planets. The [[Detached object|detached]] ETNOs, with perihelia approximately between 40–45 and 50–60&nbsp;AU, are less affected by Neptune than the scattered ETNOs, but are still relatively close to Neptune. The [[sednoid]]s or [[Hills Cloud|inner Oort cloud]] objects, with perihelia beyond 50–60&nbsp;AU, are too far from Neptune to be strongly influenced by it.<ref name="Sheppard-2018" />

Currently, there is one ETNO that is classified as a dwarf planet:
* {{Dp|Sedna}} (76.2–937&nbsp;AU) was the first extreme trans-Neptunian object to be discovered. It is a large, reddish object, and takes ~11,400&nbsp;years to complete one orbit. [[Michael E. Brown|Mike Brown]], who discovered the object in 2003, asserts that it cannot be part of the scattered disc or the Kuiper belt because its perihelion is too distant to have been affected by Neptune's migration.<ref>{{Cite web |last=Jewitt |first=David |date=2004 |title=Sedna – 2003 VB<sub>12</sub> |url=http://www2.ess.ucla.edu/~jewitt/kb/sedna.html |url-status=live |archive-url=https://web.archive.org/web/20110716032018/http://www2.ess.ucla.edu/~jewitt/kb/sedna.html |archive-date=16 July 2011 |access-date=23 June 2006 |website=University of Hawaii}}</ref> The [[Sednoid|sednoid population]] is named after Sedna.<ref name="Sheppard-2018" />

=== Edge of the heliosphere ===
[[File:Magnetosphere Levels.jpg|thumb|Diagram of the Sun's magnetosphere and helioshealth]]

{{Anchor|Heliopause}}The Sun's [[stellar-wind bubble]], the [[heliosphere]], a region of space dominated by the Sun, has its boundary at the ''termination shock''. Based on the Sun's [[peculiar motion]] relative to the [[local standard of rest]], this boundary is roughly 80–100&nbsp;AU from the Sun upwind of the interstellar medium and roughly 200&nbsp;AU from the Sun downwind.<ref name="fahr">{{Cite journal |last1=Fahr |first1=H. J. |last2=Kausch |first2=T. |last3=Scherer |first3=H. |date=2000 |title=A 5-fluid hydrodynamic approach to model the Solar System-interstellar medium interaction |url=http://aa.springer.de/papers/0357001/2300268.pdf |url-status=dead |journal=[[Astronomy & Astrophysics]] |volume=357 |page=268 |bibcode=2000A&A...357..268F |archive-url=https://web.archive.org/web/20170808135422/http://aa.springer.de/papers/0357001/2300268.pdf |archive-date=8 August 2017 |access-date=24 August 2008}} See Figures 1 and 2.</ref> Here the solar wind collides with the interstellar medium<ref>{{Cite web |last=Hatfield |first=Miles |date=3 June 2021 |title=The Heliopedia |url=http://www.nasa.gov/mission_pages/sunearth/the-heliopedia |url-status=live |archive-url=https://web.archive.org/web/20220325142928/https://www.nasa.gov/mission_pages/sunearth/the-heliopedia |archive-date=25 March 2022 |access-date=29 March 2022 |website=NASA}}</ref> and dramatically slows, condenses and becomes more turbulent, forming a great oval structure known as the [[heliosheath]].<ref name="fahr" />

The heliosheath has been theorized to look and behave very much like a comet's tail, extending outward for a further 40&nbsp;AU on the upwind side but tailing many times that distance downwind to possibly several thousands of AU.<ref name="n092">{{cite journal | last1=Brandt | first1=P. C. | last2=Provornikova | first2=E. | last3=Bale | first3=S. D. | last4=Cocoros | first4=A. | last5=DeMajistre | first5=R. | last6=Dialynas | first6=K. | last7=Elliott | first7=H. A. | last8=Eriksson | first8=S. | last9=Fields | first9=B. | last10=Galli | first10=A. | last11=Hill | first11=M. E. | last12=Horanyi | first12=M. | last13=Horbury | first13=T. | last14=Hunziker | first14=S. | last15=Kollmann | first15=P. | last16=Kinnison | first16=J. | last17=Fountain | first17=G. | last18=Krimigis | first18=S. M. | last19=Kurth | first19=W. S. | last20=Linsky | first20=J. | last21=Lisse | first21=C. M. | last22=Mandt | first22=K. E. | last23=Magnes | first23=W. | last24=McNutt | first24=R. L. | last25=Miller | first25=J. | last26=Moebius | first26=E. | last27=Mostafavi | first27=P. | last28=Opher | first28=M. | last29=Paxton | first29=L. | last30=Plaschke | first30=F. | last31=Poppe | first31=A. R. | last32=Roelof | first32=E. C. | last33=Runyon | first33=K. | last34=Redfield | first34=S. | last35=Schwadron | first35=N. | last36=Sterken | first36=V. | last37=Swaczyna | first37=P. | last38=Szalay | first38=J. | last39=Turner | first39=D. | last40=Vannier | first40=H. | last41=Wimmer-Schweingruber | first41=R. | last42=Wurz | first42=P. | last43=Zirnstein | first43=E. J. | title=Future Exploration of the Outer Heliosphere and Very Local Interstellar Medium by Interstellar Probe | journal=Space Science Reviews | volume=219 | issue=2 | date=2023 | issn=0038-6308 | pmid=36874191 | pmc=9974711 | doi=10.1007/s11214-022-00943-x | page=18| bibcode=2023SSRv..219...18B }}</ref><ref>{{Cite journal |last1=Baranov |first1=V. B. |last2=Malama |first2=Yu. G. |date=1993 |title=Model of the solar wind interaction with the local interstellar medium: Numerical solution of self-consistent problem |url=http://doi.wiley.com/10.1029/93JA01171 |journal=Journal of Geophysical Research |language=en |volume=98 |issue=A9 |page=15157 |bibcode=1993JGR....9815157B |doi=10.1029/93JA01171 |issn=0148-0227 |access-date=9 April 2022 |archive-date=20 April 2022 |archive-url=https://web.archive.org/web/20220420161220/https://onlinelibrary.wiley.com/resolve/doi?DOI=10.1029%2F93JA01171 |url-status=live }}</ref> Evidence from the ''[[Cassini (spacecraft)|Cassini]]'' and [[Interstellar Boundary Explorer]] spacecraft has suggested that it is forced into a bubble shape by the constraining action of the interstellar magnetic field,<ref>{{Cite web |date=19 November 2009 |title=Cassini's Big Sky: The View from the Center of Our Solar System |url=https://www.jpl.nasa.gov/news/cassinis-big-sky-the-view-from-the-center-of-our-solar-system |url-status=live |archive-url=https://web.archive.org/web/20220409213721/https://www.jpl.nasa.gov/news/cassinis-big-sky-the-view-from-the-center-of-our-solar-system |archive-date=9 April 2022 |access-date=9 April 2022 |website=Jet Propulsion Laboratory}}</ref><ref>{{Cite journal |last1=Kornbleuth |first1=M. |last2=Opher |first2=M. |last3=Baliukin |first3=I. |last4=Gkioulidou |first4=M. |last5=Richardson |first5=J. D. |last6=Zank |first6=G. P. |last7=Michael |first7=A. T. |last8=Tóth |first8=G. |last9=Tenishev |first9=V. |last10=Izmodenov |first10=V. |last11=Alexashov |first11=D. |date=1 December 2021 |title=The Development of a Split-tail Heliosphere and the Role of Non-ideal Processes: A Comparison of the BU and Moscow Models |journal=[[The Astrophysical Journal]] |volume=923 |issue=2 |page=179 |arxiv=2110.13962 |bibcode=2021ApJ...923..179K |doi=10.3847/1538-4357/ac2fa6 |issn=0004-637X |s2cid=239998560 |doi-access=free}}</ref> but the actual shape remains unknown.<ref>{{Cite journal |last1=Reisenfeld |first1=Daniel B. |last2=Bzowski |first2=Maciej |last3=Funsten |first3=Herbert O. |last4=Heerikhuisen |first4=Jacob |last5=Janzen |first5=Paul H. |last6=Kubiak |first6=Marzena A. |last7=McComas |first7=David J. |last8=Schwadron |first8=Nathan A. |last9=Sokół |first9=Justyna M. |last10=Zimorino |first10=Alex |last11=Zirnstein |first11=Eric J. |date=1 June 2021 |title=A Three-dimensional Map of the Heliosphere from IBEX |journal=[[The Astrophysical Journal Supplement Series]] |volume=254 |issue=2 |page=40 |bibcode=2021ApJS..254...40R |doi=10.3847/1538-4365/abf658 |issn=0067-0049 |osti=1890983 |s2cid=235400678 |doi-access=free}}</ref>

The shape and form of the outer edge of the heliosphere is likely affected by the [[fluid dynamics]] of interactions with the interstellar medium as well as [[solar magnetic field]]s prevailing to the south, e.g. it is bluntly shaped with the northern hemisphere extending 9&nbsp;AU farther than the southern hemisphere.<ref name="fahr" /> The heliopause is considered the beginning of the interstellar medium.<ref name="Voyager" /> Beyond the heliopause, at around 230&nbsp;AU, lies the [[bow shock]]: a plasma "wake" left by the Sun as it travels through the Milky Way.<ref>{{Cite APOD|date=24 June 2002|title=The Sun's Heliosphere & Heliopause|access-date=23 June 2006}}</ref> Large objects outside the heliopause remain gravitationally bound to the Sun, but the flow of matter in the interstellar medium homogenizes the distribution of micro-scale objects.<ref name="Voyager" />