View source for Orcus (dwarf planet)

{{Short description|Trans-Neptunian dwarf planet}}
{{Good article}}
{{Infobox planet
 | minorplanet     = yes
 | name            = 90482 Orcus
 | symbol          = [[File:Orcus symbol (bold).svg|24px|🝿|class=skin-invert]]
 | background      = #C2E0FF
 | image           = Orcus-Vanth orbit.gif
 | caption         = Orcus and its moon Vanth imaged by the [[Hubble Space Telescope]] in 2006
 | discovery_ref   =<ref name="jpldata" /><ref name="MPC-Orcus" />
 | discovered      = 17 February 2004
 | discoverer      = {{ubl
  | [[Michael E. Brown]]
  | [[Chad Trujillo]]
  | [[David L. Rabinowitz]]
}}
 | earliest_precovery_date = 8 November 1951
 | mpc_name        = (90482) Orcus
 | alt_names       = 2004 DW
 | pronounced      = {{IPAc-en|ˈ|ɔr|k|ə|s}}<ref>{{dict.com|Orcus}}</ref>
 | adjectives      = Orcinian {{IPAc-en|ɔr|ˈ|s|ɪ|n|i|ə|n}} (trad.),<ref>Jeremias Drexel (1641) ''A Right Intention'', page 161; ''The Freemason's Chronicle'', volume 33, page 214, 1891</ref> Orcean {{IPAc-en|ˈ|ɔr|s|i|ə|n}} (trad.)<ref>Angley (1847) ''De Clifford, the philosopher''</ref>
 | named_after     = [[Orcus]]<ref name="springer" />
 | mp_category     = {{hlist | [[Trans-Neptunian object|TNO]]<ref name="jpldata" /> |[[plutino]]<ref name="Buie" /><ref name="MPEC 2009-E53" />|[[dwarf planet]]<ref name="Grundy-orbits"/>}}
 | orbit_ref       =<ref name="jpldata" />
 | epoch           = 31 May 2020 ([[Julian day|JD]] 2459000.5)
 | uncertainty     = 2
 | observation_arc = 68.16 yr (24,894 days)
 | aphelion        = {{Convert|48.067|AU|Tm|abbr=on}}
 | perihelion      = {{Convert|30.281|AU|Tm|abbr=on}}
 | time_periastron = ≈ 10 January 2143<ref name="Horizons2143"/><br />±1 day
 | semimajor       = {{Convert|39.174|AU|Tm|abbr=on}}
 | eccentricity    = 0.22701
 | period          = 245.19 [[Julian year (astronomy)|yr]] (89,557 days)
 | mean_anomaly    = 181.735[[Degree (angle)|°]]
 | mean_motion     = {{Deg2DMS|0.00402|sup=ms}} / day
 | inclination     = 20.592°
 | asc_node        = 268.799°
 | arg_peri        = 72.310°
 | satellites      = 1 ([[Vanth (moon)|Vanth]])
 | dimensions      = {{val|910|50|40|u=km}}<ref name="brown2018"/> {{val|917|25|u=km}}<ref name=TNOsCool8 />
 | mass            = {{val|6.348|0.019|e=20|u=kg}} (Orcus and Vanth combined)<ref name="Grundy-orbits"/><br />{{val|5.47|0.10|e=20|u=kg}} (Orcus only){{efn|name=primary mass|using the most precise value of Vanth's estimated mass of {{val|8.7|0.8|e=19|u=kg}}<ref name="Brown2023"/>}}
 | density         = {{val|1.4|0.2|u=g/cm3}}<ref name="Brown2023"/>
 | surface_grav    = ≈ {{Gr|0.641|458|2}} m/s<sup>2</sup>
 | escape_velocity = ≈ {{V2|0.641|458|2}} km/s
 | spectral_type   = ([[Trans-Neptunian object#Colors|neutral]])<ref name="Barucci2008" /><br />[[Asteroid color indices|B–V]] =0.68<ref name="deBergh2005" /><br />[[Asteroid color indices|V–R]] = 0.37<ref name="deBergh2005" />
 | albedo          = {{val|0.231|0.018|0.011}}<ref name=TNOsCool8 />
 | single_temperature = < 44 [[kelvin|K]]<ref name="Barucci2008" />
 | magnitude       = 19.1 ([[Opposition (astronomy and astrology)|opposition]])<ref name="Horizons" />
 | abs_magnitude    = {{val|2.31|0.03}} (integral),<ref name=TNOsCool8 /> {{val|2.41|0.05}}<ref name="Brown2010" />
}}

'''Orcus''' ([[minor-planet designation]]: '''90482 Orcus''') is a [[dwarf planet]] located in the [[Kuiper belt]], with one large moon, [[Vanth (moon)|Vanth]].<ref name="Grundy-orbits"/> It has an estimated diameter of {{convert|870|to|960|km|mi|abbr=on}}, comparable to the [[Inner Solar System]] dwarf planet [[1 Ceres|Ceres]]. The surface of Orcus is relatively bright with [[albedo]] reaching 23 percent, neutral in color, and rich in water ice. The ice is predominantly in crystalline form, which may be related to past [[cryovolcanic]] activity. Other compounds like [[methane]] or [[ammonia]] may also be present on its surface. Orcus was discovered by American astronomers [[Michael E. Brown|Michael Brown]], [[Chad Trujillo]], and [[David L. Rabinowitz|David Rabinowitz]] on 17 February 2004.

Orcus is a [[plutino]], a [[trans-Neptunian object]] that is locked in a 2:3 [[orbital resonance]] with the [[ice giant]] [[Neptune]], making two revolutions around the Sun to every three of Neptune's.<ref name="Buie" /> This is much like [[Pluto]], except that 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" /> Orcus is the second-largest known plutino, after Pluto itself. The perihelion of Orcus's orbit is around 120° from that of Pluto, while the eccentricities and inclinations are similar. Because of these similarities and contrasts, along with its large moon [[Vanth (moon)|Vanth]] that can be compared to Pluto's large moon [[Charon (moon)|Charon]], Orcus has been dubbed the "{{nowrap|anti-Pluto}}."<ref name="MBP" /> This was a major consideration in selecting its name, as the deity [[Orcus]] was the [[Roman mythology|Roman]]/[[Etruscan mythology|Etruscan]] equivalent of the Roman/[[Greek mythology|Greek]] [[Pluto (mythology)|Pluto]].<ref name="MBP" />

== History ==
=== Discovery ===
[[File:Orcus nasa.jpg|thumb|left|upright|Discovery image of Orcus taken in 2004<ref name="distantplanetoid">{{cite web|url=https://solarsystem.nasa.gov/resources/401/distant-planetoid/|title=Distant Planetoid|publisher=NASA|website=solarsystem.nasa.gov|access-date=18 May 2019|archive-date=19 October 2020|archive-url=https://web.archive.org/web/20201019193004/https://solarsystem.nasa.gov/resources/401/distant-planetoid/|url-status=live}}</ref>]]

Orcus was discovered on 17 February 2004, by American astronomers [[Michael E. Brown|Michael Brown]] of [[California Institute of Technology|Caltech]], [[Chad Trujillo]] of the [[Gemini Observatory]], and [[David L. Rabinowitz|David Rabinowitz]] of [[Yale University]]. [[Precovery]] images taken by the [[Palomar Observatory]] as early as 8 November 1951 were later obtained from the [[Digitized Sky Survey]].<ref name="MPC-Orcus" />

=== Name and symbol ===
The [[minor planet]] Orcus was named after one of the Roman gods of the underworld, [[Orcus]]. While [[Pluto (mythology)|Pluto]] (of Greek origin) was the ruler of the underworld, Orcus (of Etruscan origin) was a punisher of the condemned. The name was published by the [[Minor Planet Center]] on 26 November 2004 ({{small|[[Minor Planet Circulars|M.P.C.]] 53177}}).<ref name="MPC-Circulars-Archive" /> Under the guidelines of the [[International Astronomical Union]]'s (IAU) [[astronomical naming conventions|naming conventions]], objects with a similar size and [[orbit]] to that of [[Pluto]] are named after [[underworld]] deities. Accordingly, the discoverers suggested naming the object after ''Orcus'', the Etruscan god of the underworld and punisher of broken oaths. The name was also a private reference to the homonymous [[Orcas Island]], where Brown's wife had lived as a child and that they visit frequently.<ref name="brown16" />

On 30 March 2005, Orcus's moon, [[Vanth (moon)|Vanth]], was named after a winged female entity, [[Vanth]], of the Etruscan underworld. She could be present at the moment of death, and frequently acted as a [[psychopomp]], a guide of the deceased to the underworld.<ref name="Johnston90482" />

The usage of [[planetary symbol]]s is no longer recommended in astronomy, so Orcus never received a symbol in the astronomical literature. A symbol {{angbr|[[File:Orcus symbol (fixed width).svg|16px|🝿]]}}, used mostly among astrologers,<ref name=miller>{{cite web|url=https://www.unicode.org/L2/L2021/21224-dwarf-planet-syms.pdf|title=Unicode request for dwarf-planet symbols|last=Miller|first=Kirk|date=26 October 2021|website=unicode.org|access-date=29 January 2022|archive-date=23 March 2022|archive-url=https://web.archive.org/web/20220323174107/https://www.unicode.org/L2/L2021/21224-dwarf-planet-syms.pdf|url-status=live}}</ref> is included in [[Unicode]] as U+1F77F.<ref>{{Cite web |url=https://www.unicode.org/alloc/Pipeline.html |title=Proposed New Characters: The Pipeline |access-date=2022-01-29 |archive-date=2022-01-29 |archive-url=https://web.archive.org/web/20220129110620/https://www.unicode.org/alloc/Pipeline.html |url-status=live }}</ref> The symbol was designed by Denis Moskowitz, a software engineer in Massachusetts; it is an OR [[monogram]], designed to resemble both a skull and an [[orca]]'s gape.<ref name=anderson>{{cite web |url=http://blog.unicode.org/2022/05/out-of-this-world-new-astronomy-symbols.html |title=Out of this World: New Astronomy Symbols Approved for the Unicode Standard |last=Anderson |first=Deborah |date=4 May 2022 |website=unicode.org |publisher=The Unicode Consortium |access-date=6 August 2022 |archive-date=6 August 2022 |archive-url=https://web.archive.org/web/20220806075352/http://blog.unicode.org/2022/05/out-of-this-world-new-astronomy-symbols.html |url-status=live }}</ref> There is a rarer symbol [[File:Orcus anti-Pluto symbol (fixed width).svg|16px]], an inverted [[Astrological symbols|astrological]] Pluto symbol, reflecting Orcus as the anti-Pluto: it was designed by Melanie Reinhart.<ref name=miller/>

== Orbit and rotation ==
Orcus is in a 2:3 orbital resonance with [[Neptune]], having an orbital period of 245 years,<ref name="Buie" /><ref name="jpldata"/> and is classified as a [[plutino]].<ref name="MPC-Orcus"/> Its orbit is moderately [[orbital inclination|inclined]] at 20.6° to the [[ecliptic]].<ref name="jpldata"/> Orcus's orbit is similar to Pluto's (both have [[Perihelion|perihelia]] above the [[ecliptic]]), but is oriented differently. Although at one point its orbit approaches that of Neptune, the resonance between the two bodies means that Orcus itself is always a great distance away from Neptune (there is always an [[angular separation]] of over 60° between them). Over a 14,000-year period, Orcus stays more than 18&nbsp;AU from Neptune.<ref name="MPC2004-D15" /> Because their mutual resonance with Neptune constrains Orcus and Pluto to remain in opposite phases of their otherwise very similar motions, Orcus is sometimes described as the "anti-Pluto".<ref name="MBP" /> Orcus last reached its [[aphelion]] (farthest distance from the Sun) in 2019 and will come to perihelion (closest distance to the Sun) around 10 January 2143.<ref name="Horizons2143"/> Simulations by the [[Deep Ecliptic Survey]] show that over the next 10 million years Orcus may acquire a perihelion distance (''q<sub>min</sub>'') as small as 27.8&nbsp;AU.<ref name="Buie" />

The rotation period of Orcus is uncertain, as different photometric surveys have produced different results. Some show low amplitude variations with periods ranging from 7 to 21 hours, whereas others show no variability.<ref name="Delsanti2010" /> The rotational axis of Orcus probably coincides with the orbital axis of its moon, Vanth. This means that Orcus is currently viewed pole-on, which could explain the near absence of any [[rotational modulation]] of its brightness.<ref name="Delsanti2010" /><ref name="Ortiz2011" /> Astronomer [[José Luis Ortiz Moreno|José Luis Ortiz]] and colleagues have derived a possible rotation period of about 10.5 hours, assuming that Orcus is not [[tidally locked]] with Vanth.<ref name="Ortiz2011">{{Cite journal | last1 = Ortiz | first1 = J. L. | last2 = Cikota | first2 = A. | last3 = Cikota | first3 = S. | last4 = Hestroffer | first4 = D. | last5 = Thirouin | first5 = A. | last6 = Morales | first6 = N. | last7 = Duffard | first7 = R. | last8 = Gil-Hutton | first8 = R. | last9 = Santos-Sanz | first9 = P. | last10 = De La Cueva | first10 = I. | title = A mid-term astrometric and photometric study of trans-Neptunian object (90482) Orcus | doi = 10.1051/0004-6361/201015309 | journal = Astronomy & Astrophysics | volume = 525 | pages = A31 | date = 2010 |bibcode = 2011A&A...525A..31O |arxiv = 1010.6187 | s2cid = 56051949 }}</ref> If, however, the primary is tidally locked with the satellite, the rotational period would coincide with the 9.7-day orbital period of Vanth.<ref name="Ortiz2011" />
{{Multiple image
| align = left
| direction = 
| width = 
| image1 = Orcus-motion.png
| width1 = 175
| caption1 = [[Mean-motion resonance]] of Orcus ([[rotating frame]] with a period equal to [[Neptune]]'s [[orbital period]])
| image2 = TheKuiperBelt Orbits Orcus2.svg
| width2 = 330
| caption2 = The orbits of Orcus (blue), Pluto (red) and Neptune (grey). Orcus and Pluto are shown in the April 2006 positions. The dates of their [[perihelia]] (q) and [[Apsis|aphelia]] (Q) are also marked.
}}
{{clear|left}}

== Physical characteristics ==
=== Size and magnitude ===
[[File:Orcus, Earth & Moon size comparison.png|left|thumb|upright|Orcus compared to [[Earth]] and the [[Moon]]]]
[[File:Orcus-apmag19-2009Dec26-11UT.jpg|left|thumb|upright|Long-exposure photograph of Orcus at visual magnitude 19.2]]

The absolute magnitude of Orcus is approximately 2.3.<ref name=TNOsCool8 /> The detection of Orcus by the [[Spitzer Space Telescope]] in the [[far infrared]]<ref name="Stansberry 2007" /> and by [[Herschel Space Telescope]] in [[submillimeter]] estimates its diameter at {{convert|958.4|km|mi|abbr=on}}, with an uncertainty of {{convert|22.9|km|mi|abbr=on}}.<ref name=TNOsCool8 /> Orcus appears to have an [[Albedo#Astronomical albedo|albedo]] of about 21–25%,<ref name=TNOsCool8 /> which may be typical of trans-Neptunian objects approaching the {{convert|1000|km|mi|abbr=on}} diameter range.<ref name="tnoalbedo" /> The magnitude and size estimates were made under the assumption that Orcus is a singular object. The presence of a relatively large satellite, Vanth, may change them considerably. The absolute magnitude of Vanth is estimated at 4.88, which means that it is about 1/11 as bright as Orcus itself.<ref name="Brown2010" /> The [[Atacama Large Millimeter Array|ALMA]] submillimeter measurements taken in 2016 showed that Vanth has a relatively large size of {{convert|475|km|mi|abbr=on}} with an albedo of about 8 percent while Orcus's has a slightly smaller size of {{convert|910|km|mi|abbr=on}}.<ref name="brown2018"/> Using a [[stellar occultation]] by Vanth in 2017, Vanth's diameter has been determined to be {{convert|442.5|km|mi|abbr=on}}, with an uncertainty of {{convert|10.2|km|mi|abbr=on}}.<ref name="Sickafoose2018"/>

=== Mass and density ===
Orcus and Vanth are known to constitute a binary system. The mass of the system has been estimated to be {{val|6.348|0.019|e=20|u=kg}},<ref name="Grundy-orbits"/> approximately equal to that of the [[Saturn]]ian moon [[Tethys (moon)|Tethys]] ({{val|6.175|e=20|u=kg}}).<ref name="Jacobson2006" /> The mass of the Orcus system is about 3.8 percent that of {{dp|Eris}}, the most massive known dwarf planet ({{val|1.66|e=22|u=kg}}).<ref name="Brown2010" /><ref name="Brown Schaller 2007" />

The ratio of the mass of Vanth to that of Orcus was measured astrometrically with the [[Atacama Large Millimeter Array|ALMA]] submillimeter telescope and is {{val|0.16|0.02}} with Vanth containing {{val|13.7|1.3|u=%}} of the total system mass. This also means that the densities of both bodies are about the same at ~{{val|1.5|u=g/cm<sup>3</sup>}}.<ref name="Brown2023"/>

=== Spectra and surface ===

The first spectroscopic observations in 2004 showed that the visible spectrum of Orcus is flat (neutral in color) and featureless, whereas in the [[near-infrared]] there were moderately strong [[water absorption]] bands at 1.5 and 2.0&nbsp;μm.<ref name="Fornasier2004" /> The neutral visible spectrum and strong water absorption bands of Orcus showed that Orcus appeared different from other trans-Neptunian objects, which typically have a red visible spectrum and often featureless [[infrared]] spectra.<ref name="Fornasier2004" /> Further infrared observations in 2004 by the [[European Southern Observatory]] and the [[Gemini telescope]] gave results consistent with mixtures of water [[ice]] and [[carbon]]aceous compounds, such as [[tholin]]s.<ref name="deBergh2005" /> The water and methane ices can cover no more than 50 percent and 30 percent of the surface, respectively.<ref name="Trujillo2005" /> This means the proportion of ice on the surface is less than on [[Charon (moon)|Charon]], but similar to that on [[Triton (moon)|Triton]].<ref name="Trujillo2005" />

Later in 2008–2010 new infrared spectroscopic observations with a higher [[signal-to-noise ratio]] revealed additional spectral features. Among them is a deep water ice absorption band at 1.65&nbsp;μm, which is evidence of the [[crystalline]] water ice on the surface of Orcus, and a new absorption band at 2.22&nbsp;μm. The origin of the latter feature is not completely clear. It can be caused either by [[ammonia]]/[[ammonium]] dissolved in the water ice or by [[methane]]/[[ethane]] ices.<ref name="Barucci2008" /> The [[radiative transfer]] modeling showed that a mixture of water ice, tholins (as a darkening agent), ethane ice, and ammonium ion (NH<sub>4</sub><sup>+</sup>) provides the best match to the spectra, whereas a combination of water ice, tholins, methane ice and ammonia hydrate gives a slightly inferior result. On the other hand, a mixture of only ammonia hydrate, tholins and water ice failed to provide a satisfactory match.<ref name="Delsanti2010" /> As of 2010, the only reliably identified compounds on the surface of Orcus are crystalline water ice and, possibly, dark tholins. A firm identification of ammonia, methane, and other [[hydrocarbon]]s requires a better infrared spectra.<ref name="Delsanti2010" />

Orcus sits at the threshold for trans-Neptunian objects massive enough to retain [[Volatile (astrogeology)|volatiles]] such as methane on the surface.<ref name="Delsanti2010" /> The reflectance spectrum of Orcus shows the deepest water-ice absorption bands of any Kuiper belt object that is not associated with the [[Haumea family|Haumea collisional family]].<ref name="Brown2010" /> The [[Moons of Uranus#Large moons|large icy satellites of Uranus]] have infrared spectra quite similar to that of Orcus.<ref name="Brown2010" /> Among other trans-Neptunian objects, the large plutino [[208996 Achlys]] and Pluto's moon Charon both have similar surface spectra to Orcus,<ref name="Barucci2008" /> with flat, featureless visible spectra and moderately strong water ice absorption bands in the near-infrared.<ref name="Delsanti2010" />

=== Cryovolcanism ===
Crystalline water ice on the surfaces of trans-Neptunian objects should be completely [[Amorphous solid|amorphized]] by the galactic and Solar radiation in about 10 million years.<ref name="Barucci2008" /> Thus the presence of [[crystal]]line water [[ice]], and possibly [[ammonia]] ice, may indicate that a renewal mechanism was active in the past on the surface of Orcus.<ref name="Barucci2008" /> Ammonia so far has not been detected on any trans-Neptunian object or icy satellite of the outer planets other than [[Miranda (moon)|Miranda]].<ref name="Barucci2008" /> The 1.65&nbsp;[[micrometre|μm]] band on Orcus is broad and deep (12%), as on Charon, {{dp|Quaoar}}, {{dp|Haumea}}, and icy satellites of the [[giant planets]].<ref name="Barucci2008" /> Some calculations indicate that [[cryovolcano|cryovolcanism]], which is considered one of the possible renewal mechanisms, may indeed be possible for trans-Neptunian objects larger than about {{convert|1000|km|mi|abbr=on}}.<ref name="Delsanti2010" /> Orcus may have experienced at least one such episode in the past, which turned the amorphous water ice on its surface into crystalline. The preferred type of volcanism may have been explosive aqueous volcanism driven by an explosive dissolution of methane from water–ammonia melts.<ref name="Delsanti2010" />

== Satellite ==
[[File:Orcus-Vanth.gif|thumb|Orcus and Vanth imaged by Hubble in 2006]]
{{main|Vanth (moon)}}

Orcus has one known moon, Vanth (formal designation {{nowrap|(90482) Orcus I}}). It was discovered by [[Michael E. Brown|Michael Brown]] and T.-A. Suer using discovery images taken by the [[Hubble Space Telescope]] on 13 November 2005.<ref name=IAUC8812 /> The discovery was announced in an [[IAU Circular]] notice published on 22 February 2007.<ref name=johnston90482>{{cite web
 |date=4 March 2007
 |title=(90482) Orcus
 |publisher=Johnston's Archive
 |author=Wm. Robert Johnston
 |url=http://www.johnstonsarchive.net/astro/astmoons/am-90482.html
 |access-date=26 March 2009
 |archive-date=10 February 2009
 |archive-url=https://web.archive.org/web/20090210205551/http://www.johnstonsarchive.net/astro/astmoons/am-90482.html
 |url-status=live
 }}</ref> A spatially resolved submillimeter imaging of Orcus–Vanth system in 2016 showed that Vanth has a relatively large size of {{convert|475|km|mi|abbr=on}}, with an uncertainty of {{convert|75|km|mi|abbr=on}}.<ref name="brown2018"/> That estimate for Vanth is in good agreement with the size of about {{convert|442.5|km|mi|abbr=on}} derived from a stellar occultation in 2017.<ref name="Sickafoose2018"/> Like Charon compared to Pluto, Vanth is quite large compared to Orcus, and is one reason for characterizing Orcus as the 'anti-Pluto'.Vanth is the third-largest known dwarf-planet moon, after Charon and [[Dysnomia (moon)|Dysnomia]]. The ratio of masses of Orcus and Vanth is uncertain, possibly anywhere from 1:33 to 1:12.<ref name="Carry2011" />

== See also ==
* [[List of possible dwarf planets]]
* [[List of trans-Neptunian objects]]
* [[List of Solar System objects by size]]
{{Clear}}

== Notes ==
{{notelist}}

== References ==
{{Reflist
| refs =

<ref name=IAUC8812>{{cite web
 |date=22 February 2007
 |title=IAUC 8812: Sats OF 2003 AZ_84, (50000), (55637), (90482)
 |publisher=International Astronomical Union Circular
 |author=Daniel W. E. Green
 |url=http://www.cbat.eps.harvard.edu/iauc/08800/08812.html
 |access-date=4 July 2011
 |archive-date=19 July 2011
 |archive-url=https://web.archive.org/web/20110719205520/http://cbat.eps.harvard.edu/iauc/08800/08812.html
 |url-status=live
 }}</ref>

<ref name=TNOsCool8>{{cite journal|first1=S.|last1=Fornasier |first2=E. |last2=Lellouch |first3=T. |last3=Müller, P. |display-authors=etal |date=2013|arxiv=1305.0449v2|title=TNOs are Cool: A survey of the trans-Neptunian region. VIII. Combined Herschel PACS and SPIRE observations of 9 bright targets at 70–500 ''μ''m.|journal=Astronomy & Astrophysics|volume=555|pages=A92|doi=10.1051/0004-6361/201321329
|bibcode = 2013A&A...555A..15F |s2cid=54222700 }}</ref>

<ref name="jpldata">{{cite web
 |type         = 2020-01-04 last obs.
 |title        = JPL Small-Body Database Browser: 90482 Orcus (2004 DW)
 |url          = http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2090482
 |publisher    = Jet Propulsion Laboratory
 |date         = 29 January 2020
 |access-date  = 20 February 2020
 |archive-date = 8 July 2019
 |archive-url  = https://web.archive.org/web/20190708202911/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2090482
 |url-status   = live
}}</ref>

<ref name="springer">{{cite book
  |last       = Schmadel | first = Lutz D.
  |title = Dictionary of Minor Planet Names |chapter = (90482) Orcus &#91;39.5, 0.22, 20.5&#93; |publisher  = Springer Berlin Heidelberg
  |page       = 236
  |date       = 2006
  |isbn       = 978-3-540-34361-5
  |doi       = 10.1007/978-3-540-34361-5_2818 }}</ref>

<ref name="MPC-Orcus">{{cite web
  |title      = 90482 Orcus (2004 DW)
  |work      = Minor Planet Center
  |url      = http://www.minorplanetcenter.net/db_search/show_object?object_id=90482
  |access-date      = 3 April 2017
  |archive-date      = 3 April 2017
  |archive-url      = https://web.archive.org/web/20170403194746/http://www.minorplanetcenter.net/db_search/show_object?object_id=90482
  |url-status      = live
  }}</ref>

<ref name="MPC-Circulars-Archive">{{cite web
  |title      = MPC/MPO/MPS Archive
  |work      = Minor Planet Center
  |url      = http://www.minorplanetcenter.net/iau/ECS/MPCArchive/MPCArchive_TBL.html
  |access-date      = 3 April 2017
  |archive-date      = 5 March 2019
  |archive-url      = https://web.archive.org/web/20190305034952/https://minorplanetcenter.net/iau/ECS/MPCArchive/MPCArchive_TBL.html
  |url-status      = live
  }}</ref>

<ref name="Buie">{{cite web
| author = Buie, Marc W.
| date = 22 December 2007
| title = Orbit Fit and Astrometric record for 90482
| publisher = SwRI (Space Science Department)
|url=http://www.boulder.swri.edu/~buie/kbo/astrom/90482.html
| access-date = 19 September 2008
| author-link = Marc W. Buie
| archive-date = 20 January 2012
| archive-url=https://web.archive.org/web/20120120082132/http://www.boulder.swri.edu/~buie/kbo/astrom/90482.html
| url-status = live
}}</ref>

<ref name="MPEC 2009-E53">{{cite web
| title = MPEC 2009-E53 :Distant Minor Planets (2009 MAR. 30.0 TT)
| date = 11 March 2009
| publisher = Minor Planet Center
|url=http://www.minorplanetcenter.net/mpec/K09/K09E53.html
| access-date = 5 July 2011
| archive-date = 13 November 2013
| archive-url=https://web.archive.org/web/20131113151853/http://www.minorplanetcenter.net/mpec/K09/K09E53.html
| url-status = live
}}</ref>

<ref name="Carry2011">{{Cite journal |ref=CITEREFCarry2011| last1 = Carry | first1 = B. | last2 = Hestroffer | first2 = D. | last3 = Demeo | first3 = F. E. | last4 = Thirouin | first4 = A. | last5 = Berthier | first5 = J. | last6 = Lacerda | first6 = P. | last7 = Sicardy | first7 = B. | last8 = Doressoundiram | first8 = A. | last9 = Dumas | first9 = C. | last10 = Farrelly | first10 = D. | last11 = Müller | first11 = T. G. | title = Integral-field spectroscopy of (90482) Orcus–Vanth | arxiv = 1108.5963| doi = 10.1051/0004-6361/201117486 | journal = Astronomy & Astrophysics | volume = 534 | pages = A115 | date = 2011 |bibcode = 2011A&A...534A.115C | s2cid = 118524500 }}</ref>

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{{cite book
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{{cite journal
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{{cite journal
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<ref name="Horizons">{{cite web
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<ref name="MBP">
{{cite web
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<ref name="MPC2004-D15">{{cite web
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{{cite journal
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{{cite web
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<ref name="Johnston90482">
{{cite web
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| title = (90482) Orcus
| publisher = Johnston's Archive
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<ref name="brown2018">{{cite journal
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<ref name="Brown Schaller 2007">{{cite journal
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<ref name="Grundy-orbits">{{cite journal
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<ref name="Brown2023">{{cite journal |last1=Brown |first1=Michael E. |last2=Butler |first2=Bryan J. |title=Masses and Densities of Dwarf Planet Satellites Measured with ALMA |journal=The Planetary Science Journal |date=1 October 2023 |volume=4 |issue=10 |pages=193 |doi=10.3847/PSJ/ace52a|doi-access=free |arxiv=2307.04848 |bibcode=2023PSJ.....4..193B }}</ref>

<ref name="Horizons2143">{{cite web
  |title=Horizons Batch for 90482 Orcus on 2143-Jan-10
  |publisher=[[JPL Horizons On-Line Ephemeris System|JPL Horizons]]
  |type=Perihelion occurs when rdot flips from negative to positive
  |url=https://ssd.jpl.nasa.gov/api/horizons.api?format=text&COMMAND=%2790482%27&START_TIME=%272143-Jan-05%27&STOP_TIME=%272143-Jan-15%27&STEP_SIZE=%273%20hours%27&QUANTITIES=%2719%27
  |accessdate=2023-08-27}} (JPL#48/Soln.date: 2023-Aug-25)</ref>

}} <!-- end of refs -->

== External links ==
{{Commons category}}
* [http://www.minorplanetcenter.net/mpec/K04/K04D09.html MPEC 2004-D09] announcing the discovery {{small|but attributing it to Raymond J. Bambery, Steven H. Pravdo, Michael D. Hicks, [[Kenneth J. Lawrence]], Daniel MacDonald, [[Eleanor Helin]] and Robert Thicksten / [[Near-Earth Asteroid Tracking|NEAT]]}}
* [http://www.minorplanetcenter.net/mpec/K04/K04D13.html MPEC 2004-D13] correcting MPEC 2004-D09
* [https://web.archive.org/web/20070322195011/http://www.chadtrujillo.com/2004dw/ Chad Trujillo's page on 2004 DW]
* [https://apod.nasa.gov/apod/ap090325.html Orcus of the Outer Solar System], [[Astronomy Picture of the Day]], 25 March 2009
* [http://news.bbc.co.uk/2/hi/science/nature/3506329.stm New world found far beyond Pluto], David Whitehouse, ''BBC News'', 3 March 2004
* [https://skyandtelescope.org/astronomy-news/a-new-kuiper-belt-giant/ A New Kuiper Belt Giant], Stuart Goldman, ''Sky & Telescope'', 24 February 2004
* {{JPL small body|id=90482}}

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{{DEFAULTSORT:090482}}
[[Category:90482 Orcus| ]]
[[Category:Dwarf planets]]
[[Category:Plutinos]]
[[Category:Discoveries by Michael E. Brown|Orcus]]
[[Category:Discoveries by Chad Trujillo|Orcus]]
[[Category:Discoveries by David L. Rabinowitz|Orcus]]
[[Category:Named minor planets|Orcus]]
[[Category:Astronomical objects discovered in 2004|20040217]]