Editing Orcus (dwarf planet) (section)

{{Short description|Trans-Neptunian dwarf planet}}
{{About||the Roman god|Orcus (mythology)|other uses|Orcus (disambiguation)}}
{{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" />