Editing Pluto (section)

== Natural satellites ==
{{main|Moons of Pluto}}
[[File:Pluto-Charon system-new.gif|alt=|thumb|upright=1.28|An oblique view of the Pluto–Charon system, showing that Pluto orbits a point outside itself. The two bodies are mutually [[tidally locked]].]]
[[File:Nh-pluto moons family portrait.png|thumb|Five known moons of Pluto to scale]]
Pluto has five known [[natural satellite]]s. The largest and closest to Pluto is [[Charon (moon)|Charon]]. First identified in 1978 by astronomer [[James Christy]], Charon is the only moon of Pluto that may be in [[hydrostatic equilibrium]]. Charon's mass is sufficient to cause the barycenter of the Pluto–Charon system to be outside Pluto. Beyond Charon there are four much smaller [[circumbinary]] moons. In order of distance from Pluto they are Styx, Nix, Kerberos, and Hydra. [[Nix (moon)|Nix]] and [[Hydra (moon)|Hydra]] were both discovered in 2005,<ref name="Gugliotta2005" /> [[Kerberos (moon)|Kerberos]] was discovered in 2011,<ref name="P4" /> and [[Styx (moon)|Styx]] was discovered in 2012.<ref>{{cite news |url=http://www.space.com/16531-pluto-fifth-moon-hubble-discovery.html |title=Pluto Has a Fifth Moon, Hubble Telescope Reveals |last=Wall |first=Mike |date=July 11, 2012 |work=Space.com |access-date=July 11, 2012 |archive-date=May 14, 2020 |archive-url=https://web.archive.org/web/20200514184955/https://www.space.com/16531-pluto-fifth-moon-hubble-discovery.html |url-status=live }}</ref> The satellites' orbits are circular (eccentricity < 0.006) and coplanar with Pluto's equator (inclination < 1°),<ref name="Buie2012">{{cite journal |journal=The Astronomical Journal |last1=Buie |first1=M. |last2=Tholen |first2=D. |last3=Grundy |first3=W. |title=The Orbit of Charon is Circular |year=2012 |volume=144 |issue=1 |pages=15 |doi=10.1088/0004-6256/144/1/15 |bibcode=2012AJ....144...15B|s2cid=15009477 |url=http://pdfs.semanticscholar.org/bfb8/1eb1887c28df5f5348a491cff7d4870e8c77.pdf |archive-url=https://web.archive.org/web/20200412141438/http://pdfs.semanticscholar.org/bfb8/1eb1887c28df5f5348a491cff7d4870e8c77.pdf |url-status=dead |archive-date=April 12, 2020}}</ref><ref name="ShowalterHamilton2015" /> and therefore tilted approximately 120° relative to Pluto's orbit. The Plutonian system is highly compact: the five known satellites orbit within the inner 3% of the region where [[prograde orbit]]s would be stable.<ref name="Sternetal 2005" />

The orbital periods of all Pluto's moons are linked in a system of [[orbital resonance]]s and [[Orbital resonance#Coincidental 'near' ratios of mean motion|near-resonances]].<ref name="ShowalterHamilton2015">{{cite journal |last1=Showalter |first1=M.R. |author1-link=Mark R. Showalter |last2=Hamilton |first2=D.P. |title=Resonant interactions and chaotic rotation of Pluto's small moons |journal=Nature |volume=522 |issue=7554 |date=June 3, 2015 |pages=45–49 |doi=10.1038/nature14469 |bibcode=2015Natur.522...45S |pmid=26040889 |s2cid=205243819}}</ref><ref name="Witze2015">{{cite journal |last=Witze |first=Alexandra |title=Pluto's moons move in synchrony |journal=Nature |year=2015 |doi=10.1038/nature.2015.17681 |s2cid=134519717}}</ref> When [[Apsidal precession|precession]] is accounted for, the orbital periods of Styx, Nix, and Hydra are in an exact 18:22:33 ratio.<ref name="ShowalterHamilton2015" /> There is a sequence of approximate ratios, 3:4:5:6, between the periods of Styx, Nix, Kerberos, and Hydra with that of Charon; the ratios become closer to being exact the further out the moons are.<ref name="ShowalterHamilton2015" /><ref name="Matson">{{cite web |last=Matson |first=J. |date=July 11, 2012 |title=New Moon for Pluto: Hubble Telescope Spots a 5th Plutonian Satellite |work=[[Scientific American]] web site |url=http://www.scientificamerican.com/article.cfm?id=pluto-moon-p5 |access-date=July 12, 2012 |archive-date=August 31, 2016 |archive-url=https://web.archive.org/web/20160831015135/http://www.scientificamerican.com/article.cfm?id=pluto-moon-p5 |url-status=live }}</ref>

The Pluto–Charon system is one of the few in the Solar System whose barycenter lies outside the primary body; the [[617 Patroclus|Patroclus–Menoetius]] system is a smaller example, and the [[Jupiter#Size and mass|Sun–Jupiter]] system is the only larger one.<ref name="RichardsonWalsh2005" /> The similarity in size of Charon and Pluto has prompted some astronomers to call it a [[Double planet|double dwarf planet]].<ref name="Sicardyetal2006nature" /> The system is also unusual among planetary systems in that each is [[tidally locked]] to the other, which means that Pluto and Charon always have the same hemisphere facing each other — a property shared by only one other known system, [[Eris (dwarf planet)|Eris]] and [[Dysnomia (moon)|Dysnomia]].<ref name="Szakats2022">{{cite journal |display-authors=etal |last1=Szakáts |first1=R. |last2=Kiss |first2=Cs. |last3=Ortiz |first3=J.L. |last4=Morales |first4=N. |last5=Pál |first5=A. |last6=Müller |first6=T.G. |title=Tidally locked rotation of the dwarf planet (136199) Eris discovered from long-term ground based and space photometry |journal=Astronomy & Astrophysics |volume=L3 |page=669 |year=2023 |arxiv=2211.07987 |bibcode=2023A&A...669L...3S |s2cid=253522934 |doi=10.1051/0004-6361/202245234}}</ref> From any position on either body, the other is always at the same position in the sky, or always obscured.<ref name="Young1997" /> This also means that the rotation period of each is equal to the time it takes the entire system to rotate around its barycenter.<ref name="axis" />

Pluto's moons are hypothesized to have been formed by a collision between Pluto and a similar-sized body, early in the history of the Solar System. The collision released material that consolidated into the moons around Pluto.<ref name="nasa.gov">{{cite web |title=NASA's Hubble Finds Pluto's Moons Tumbling in Absolute Chaos |url=http://www.nasa.gov/press-release/nasa-s-hubble-finds-pluto-s-moons-tumbling-in-absolute-chaos |date=June 3, 2015 |access-date=June 3, 2015 |archive-date=April 6, 2020 |archive-url=https://web.archive.org/web/20200406161853/https://www.nasa.gov/press-release/nasa-s-hubble-finds-pluto-s-moons-tumbling-in-absolute-chaos |url-status=live }}</ref><!--Kerberos has a much lower albedo than the other moons of Pluto,<ref name="spaceweirdmoons">{{cite web |title=Pluto's moons are even weirder than thought |url=http://www.space.com/29559-pluto-moons-weird-orbit-chaos.html |access-date=June 20, 2015}}</ref> which is difficult to explain with a giant collision.<ref name="nationalgeorandombeat">{{cite web |title=Pluto's moons dance to a random beat |url=http://news.nationalgeographic.com/2015/06/150603-pluto-moons-charon-styx-nix-kerberos-hydra-new-horizons/ |archive-url=https://web.archive.org/web/20150603215824/http://news.nationalgeographic.com/2015/06/150603-pluto-moons-charon-styx-nix-kerberos-hydra-new-horizons/ |url-status=dead |archive-date=June 3, 2015 |access-date=June 20, 2015}}</ref>-->{{clear}}

=== Quasi-satellite ===
In 2012, it was calculated that [[15810 Arawn]] could be a [[quasi-satellite]] of Pluto, a specific type of co-orbital configuration.<ref name="quasi" /> According to the calculations, the object would be a quasi-satellite of Pluto for about 350,000 years out of every two-million-year period.<ref name="quasi" /><ref name="S&T" /> Measurements made by the ''New Horizons'' spacecraft in 2015 made it possible to calculate the orbit of Arawn more accurately,<ref name="2016maynasa">{{cite web|title=New Horizons Collects First Science on a Post-Pluto Object|url=http://www.nasa.gov/feature/new-horizons-collects-first-science-on-a-post-pluto-object|publisher=NASA|date=May 13, 2016|access-date=June 5, 2016|archive-date=June 7, 2016|archive-url=https://web.archive.org/web/20160607150433/http://www.nasa.gov/feature/new-horizons-collects-first-science-on-a-post-pluto-object/|url-status=dead}}</ref> and confirmed the earlier ones.<ref name="analemma">{{cite journal |title=The analemma criterion: accidental quasi-satellites are indeed true quasi-satellites |first1=Carlos |last1=de la Fuente Marcos |last2=de la Fuente Marcos |first2=Raúl |journal=[[Monthly Notices of the Royal Astronomical Society]] |date=2016 |volume=462 |issue=3 |pages=3344–3349 |arxiv=1607.06686 |doi=10.1093/mnras/stw1833 |doi-access=free |bibcode=2016MNRAS.462.3344D|s2cid=119284843 }}</ref> However, it is not agreed upon among astronomers whether Arawn should be classified as a quasi-satellite of Pluto based on its orbital dynamics, since its orbit is primarily controlled by Neptune with only occasional perturbations by Pluto.<ref name="porter_et_al_2016">{{cite journal |title=The First High-phase Observations of a KBO: New Horizons Imaging of (15810) 1994 JR1 from the Kuiper Belt |first=Simon B. |last=Porter |display-authors=etal |journal=[[The Astrophysical Journal Letters]] |volume=828 |issue=2 |pages=L15 |date=2016 |arxiv=1605.05376 |bibcode=2016ApJ...828L..15P |doi=10.3847/2041-8205/828/2/L15|s2cid=54507506 |doi-access=free }}</ref><ref name="2016maynasa" /><ref name=analemma />