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<title>Orcus (dwarf planet)</title>

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Orcus (dwarf planet)

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</style><table class="infobox"><caption class="infobox-title fn org">90482 Orcus</caption><tbody><tr><td colspan="2" class="infobox-image"><div class="infobox-caption">Orcus and its moon Vanth imaged by the <a href="Hubble_Space_Telescope" title="Hubble Space Telescope">Hubble Space Telescope</a> in 2006</div></td></tr><tr><th colspan="2" class="infobox-header" style="background-color:#C2E0FF">Discovery<a href="#cite_note-jpldata-1">[1]</a><a href="#cite_note-MPC-Orcus-2">[2]</a></th></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="List_of_minor_planet_discoverers" title="List of minor planet discoverers">Discovered by</a></th><td class="infobox-data"><style data-mw-deduplicate="TemplateStyles:r1126788409">

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</style><div class="plainlist"><ul><li><a href="Michael_E._Brown" title="Michael E. Brown">Michael E. Brown</a></li><li><a href="Chad_Trujillo" title="Chad Trujillo">Chad Trujillo</a></li><li><a href="David_L._Rabinowitz" title="David L. Rabinowitz">David L. Rabinowitz</a></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;">Discovery date</th><td class="infobox-data">17 February 2004</td></tr><tr><th colspan="2" class="infobox-header" style="background-color:#C2E0FF">Designations</th></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Minor-planet_designation" title="Minor-planet designation">MPC designation</a></div></th><td class="infobox-data">(90482) Orcus</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;">Pronunciation</th><td class="infobox-data">/ˈɔːrkəs/<a href="#cite_note-3">[3]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Named after</div></th><td class="infobox-data"><a href="Orcus" title="Orcus">Orcus</a><a href="#cite_note-springer-4">[4]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Provisional_designation_in_astronomy" title="Provisional designation in astronomy">Alternative designations</a></div></th><td class="infobox-data">2004 DW</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Minor_planet#Populations" title="Minor planet">Minor planet category</a></div></th><td class="infobox-data"><style data-mw-deduplicate="TemplateStyles:r1129693374">

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</style><div class="hlist"><ul><li><a href="Trans-Neptunian_object" title="Trans-Neptunian object">TNO</a><a href="#cite_note-jpldata-1">[1]</a></li><li><a href="Plutino" title="Plutino">plutino</a><a href="#cite_note-Buie-5">[5]</a><a href="#cite_note-MPEC_2009-E53-6">[6]</a></li><li><a href="Dwarf_planet" title="Dwarf planet">dwarf planet</a><a href="#cite_note-Grundy-orbits-7">[7]</a></li></ul></div></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="List_of_adjectivals_and_demonyms_of_astronomical_bodies" title="List of adjectivals and demonyms of astronomical bodies">Adjectives</a></th><td class="infobox-data">Orcinian /ɔːrˈsɪniən/ (trad.),<a href="#cite_note-8">[8]</a> Orcean /ˈɔːrsiən/ (trad.)<a href="#cite_note-9">[9]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="Planet_symbols" class="mw-redirect" title="Planet symbols">Symbol</a></th><td class="infobox-data"></td></tr><tr><th colspan="2" class="infobox-header" style="background-color:#C2E0FF"><a href="Osculating_orbit" title="Osculating orbit">Orbital characteristics</a><a href="#cite_note-jpldata-1">[1]</a></th></tr><tr><td colspan="2" class="infobox-full-data"><a href="Epoch_(astronomy)" title="Epoch (astronomy)">Epoch</a> 31 May 2020 (<a href="Julian_day" title="Julian day">JD</a> 2459000.5)</td></tr><tr><td colspan="2" class="infobox-full-data"><a href="Uncertainty_parameter" title="Uncertainty parameter">Uncertainty parameter</a> 2</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="Observation_arc" title="Observation arc">Observation arc</a></th><td class="infobox-data">68.16 yr (24,894 days)</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;">Earliest <a href="Precovery" title="Precovery">precovery</a> date</th><td class="infobox-data">8 November 1951</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="Perihelion_and_aphelion" class="mw-redirect" title="Perihelion and aphelion">Aphelion</a></th><td class="infobox-data">48.067 AU (7.1907 Tm)</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="Perihelion_and_aphelion" class="mw-redirect" title="Perihelion and aphelion">Perihelion</a></th><td class="infobox-data">30.281 AU (4.5300 Tm)</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Semi-major_and_semi-minor_axes" title="Semi-major and semi-minor axes">Semi-major axis</a></div></th><td class="infobox-data">39.174 AU (5.8603 Tm)</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="Orbital_eccentricity" title="Orbital eccentricity">Eccentricity</a></th><td class="infobox-data">0.22701</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Orbital_period" title="Orbital period">Orbital period (sidereal)</a></div></th><td class="infobox-data">245.19 <a href="Julian_year_(astronomy)" title="Julian year (astronomy)">yr</a> (89,557 days)</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Mean_anomaly#Mean_anomaly_at_epoch" title="Mean anomaly">Mean anomaly</a></div></th><td class="infobox-data">181.735<a href="Degree_(angle)" title="Degree (angle)">°</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Mean_motion" title="Mean motion">Mean motion</a></div></th><td class="infobox-data">0° 0m 14.472s / day</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="Orbital_inclination" title="Orbital inclination">Inclination</a></th><td class="infobox-data">20.592°</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Longitude_of_the_ascending_node" title="Longitude of the ascending node">Longitude of ascending node</a></div></th><td class="infobox-data">268.799°</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Apsis" title="Apsis">Time of perihelion</a></div></th><td class="infobox-data">≈ 10 January 2143<a href="#cite_note-Horizons2143-10">[10]</a> ±1 day</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Argument_of_periapsis" title="Argument of periapsis">Argument of perihelion</a></div></th><td class="infobox-data">72.310°</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;">Known <a href="Natural_satellite" title="Natural satellite">satellites</a></th><td class="infobox-data">1 (<a href="Vanth_(moon)" title="Vanth (moon)">Vanth</a>)</td></tr><tr><th colspan="2" class="infobox-header" style="background-color:#C2E0FF"><a href="Standard_asteroid_physical_characteristics" title="Standard asteroid physical characteristics">Physical characteristics</a></th></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="Mean_radius_(astronomy)" title="Mean radius (astronomy)">Dimensions</a></th><td class="infobox-data">910+50 −40 km<a href="#cite_note-brown2018-11">[11]</a> 917±25 km<a href="#cite_note-TNOsCool8-12">[12]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="Mass" title="Mass">Mass</a></th><td class="infobox-data">(6.348±0.019)×1020 kg (Orcus and Vanth combined)<a href="#cite_note-Grundy-orbits-7">[7]</a> (5.47±0.10)×1020 kg (Orcus only)<a href="#cite_note-primary_mass-14">[a]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Mean <a href="Density" title="Density">density</a></div></th><td class="infobox-data">1.4±0.2 g/cm3<a href="#cite_note-Brown2023-13">[13]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Equatorial <a href="Standard_asteroid_physical_characteristics#Surface_gravity" title="Standard asteroid physical characteristics">surface gravity</a></div></th><td class="infobox-data">≈ 0.2 m/s2</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Equatorial <a href="Escape_velocity" title="Escape velocity">escape velocity</a></div></th><td class="infobox-data">≈ 0.43 km/s</td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Geometric_albedo" title="Geometric albedo">Geometric albedo</a></div></th><td class="infobox-data">0.231+0.018 −0.011<a href="#cite_note-TNOsCool8-12">[12]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><a href="Temperature" title="Temperature">Temperature</a></th><td class="infobox-data">< 44 <a href="Kelvin" title="Kelvin">K</a><a href="#cite_note-Barucci2008-15">[14]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Asteroid_spectral_types" title="Asteroid spectral types">Spectral type</a></div></th><td class="infobox-data">(<a href="Trans-Neptunian_object#Colors" title="Trans-Neptunian object">neutral</a>)<a href="#cite_note-Barucci2008-15">[14]</a> <a href="Asteroid_color_indices" class="mw-redirect" title="Asteroid color indices">B–V</a> =0.68<a href="#cite_note-deBergh2005-16">[15]</a> <a href="Asteroid_color_indices" class="mw-redirect" title="Asteroid color indices">V–R</a> = 0.37<a href="#cite_note-deBergh2005-16">[15]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Apparent_magnitude" title="Apparent magnitude">Apparent magnitude</a></div></th><td class="infobox-data">19.1 (<a href="Opposition_(astronomy_and_astrology)" class="mw-redirect" title="Opposition (astronomy and astrology)">opposition</a>)<a href="#cite_note-Horizons-17">[16]</a></td></tr><tr><th scope="row" class="infobox-label" style="max-width:11em;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="Absolute_magnitude#Solar_System_bodies_(H)" title="Absolute magnitude">Absolute magnitude (H)</a></div></th><td class="infobox-data">2.31±0.03 (integral),<a href="#cite_note-TNOsCool8-12">[12]</a> 2.41±0.05<a href="#cite_note-Brown2010-18">[17]</a></td></tr><tr><td colspan="2" class="infobox-below"><style data-mw-deduplicate="TemplateStyles:r1239543626">

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Orcus (<a href="Minor-planet_designation" title="Minor-planet designation">minor-planet designation</a>: 90482 Orcus) is a <a href="Dwarf_planet" title="Dwarf planet">dwarf planet</a> located in the <a href="Kuiper_belt" title="Kuiper belt">Kuiper belt</a>, with one large moon, <a href="Vanth_(moon)" title="Vanth (moon)">Vanth</a>.<a href="#cite_note-Grundy-orbits-7">[7]</a> It has an estimated diameter of 870 to 960 km (540 to 600 mi), comparable to the <a href="Inner_Solar_System" class="mw-redirect" title="Inner Solar System">Inner Solar System</a> dwarf planet <a href="1_Ceres" class="mw-redirect" title="1 Ceres">Ceres</a>. The surface of Orcus is relatively bright with <a href="Albedo" title="Albedo">albedo</a> reaching 23 percent, neutral in color, and rich in water ice. The ice is predominantly in crystalline form, which may be related to past <a href="Cryovolcanic" class="mw-redirect" title="Cryovolcanic">cryovolcanic</a> activity. Other compounds like <a href="Methane" title="Methane">methane</a> or <a href="Ammonia" title="Ammonia">ammonia</a> may also be present on its surface. Orcus was discovered by American astronomers <a href="Michael_E._Brown" title="Michael E. Brown">Michael Brown</a>, <a href="Chad_Trujillo" title="Chad Trujillo">Chad Trujillo</a>, and <a href="David_L._Rabinowitz" title="David L. Rabinowitz">David Rabinowitz</a> on 17 February 2004.

Orcus is a <a href="Plutino" title="Plutino">plutino</a>, a <a href="Trans-Neptunian_object" title="Trans-Neptunian object">trans-Neptunian object</a> that is locked in a 2:3 <a href="Orbital_resonance" title="Orbital resonance">orbital resonance</a> with the <a href="Ice_giant" title="Ice giant">ice giant</a> <a href="Neptune" title="Neptune">Neptune</a>, making two revolutions around the Sun to every three of Neptune's.<a href="#cite_note-Buie-5">[5]</a> This is much like <a href="Pluto" title="Pluto">Pluto</a>, except that the <a href="Phase_(waves)#Phase_difference" title="Phase (waves)">phase</a> of Orcus's orbit is opposite to Pluto's: Orcus is at <a href="Aphelion" class="mw-redirect" title="Aphelion">aphelion</a> (most recently in 2019) around when Pluto is at <a href="Perihelion" class="mw-redirect" title="Perihelion">perihelion</a> (most recently in 1989) and vice versa.<a href="#cite_note-MPC2004-D15-19">[18]</a> 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 <a href="Vanth_(moon)" title="Vanth (moon)">Vanth</a> that can be compared to Pluto's large moon <a href="Charon_(moon)" title="Charon (moon)">Charon</a>, Orcus has been dubbed the "anti-Pluto."<a href="#cite_note-MBP-20">[19]</a> This was a major consideration in selecting its name, as the deity <a href="Orcus" title="Orcus">Orcus</a> was the <a href="Roman_mythology" title="Roman mythology">Roman</a>/<a href="Etruscan_mythology" class="mw-redirect" title="Etruscan mythology">Etruscan</a> equivalent of the Roman/<a href="Greek_mythology" title="Greek mythology">Greek</a> <a href="Pluto_(mythology)" title="Pluto (mythology)">Pluto</a>.<a href="#cite_note-MBP-20">[19]</a>

<div class="mw-heading mw-heading2"><h2 id="History">History</h2></div>

<div class="mw-heading mw-heading3"><h3 id="Discovery">Discovery</h3></div>

Orcus was discovered on 17 February 2004, by American astronomers <a href="Michael_E._Brown" title="Michael E. Brown">Michael Brown</a> of <a href="California_Institute_of_Technology" title="California Institute of Technology">Caltech</a>, <a href="Chad_Trujillo" title="Chad Trujillo">Chad Trujillo</a> of the <a href="Gemini_Observatory" title="Gemini Observatory">Gemini Observatory</a>, and <a href="David_L._Rabinowitz" title="David L. Rabinowitz">David Rabinowitz</a> of <a href="Yale_University" title="Yale University">Yale University</a>. <a href="Precovery" title="Precovery">Precovery</a> images taken by the <a href="Palomar_Observatory" title="Palomar Observatory">Palomar Observatory</a> as early as 8 November 1951 were later obtained from the <a href="Digitized_Sky_Survey" title="Digitized Sky Survey">Digitized Sky Survey</a>.<a href="#cite_note-MPC-Orcus-2">[2]</a>

<div class="mw-heading mw-heading3"><h3 id="Name_and_symbol">Name and symbol</h3></div>

The <a href="Minor_planet" title="Minor planet">minor planet</a> Orcus was named after one of the Roman gods of the underworld, <a href="Orcus" title="Orcus">Orcus</a>. While <a href="Pluto_(mythology)" title="Pluto (mythology)">Pluto</a> (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 <a href="Minor_Planet_Center" title="Minor Planet Center">Minor Planet Center</a> on 26 November 2004 (<a href="Minor_Planet_Circulars" class="mw-redirect" title="Minor Planet Circulars">M.P.C.</a> 53177).<a href="#cite_note-MPC-Circulars-Archive-22">[21]</a> Under the guidelines of the <a href="International_Astronomical_Union" title="International Astronomical Union">International Astronomical Union</a>'s (IAU) <a href="Astronomical_naming_conventions" title="Astronomical naming conventions">naming conventions</a>, objects with a similar size and <a href="Orbit" title="Orbit">orbit</a> to that of <a href="Pluto" title="Pluto">Pluto</a> are named after <a href="Underworld" title="Underworld">underworld</a> 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 <a href="Orcas_Island" title="Orcas Island">Orcas Island</a>, where Brown's wife had lived as a child and that they visit frequently.<a href="#cite_note-brown16-23">[22]</a>

On 30 March 2005, Orcus's moon, <a href="Vanth_(moon)" title="Vanth (moon)">Vanth</a>, was named after a winged female entity, <a href="Vanth" title="Vanth">Vanth</a>, of the Etruscan underworld. She could be present at the moment of death, and frequently acted as a <a href="Psychopomp" title="Psychopomp">psychopomp</a>, a guide of the deceased to the underworld.<a href="#cite_note-Johnston90482-24">[23]</a>

The usage of <a href="Planetary_symbol" class="mw-redirect" title="Planetary symbol">planetary symbols</a> is no longer recommended in astronomy, so Orcus never received a symbol in the astronomical literature. A symbol ⟨⟩, used mostly among astrologers,<a href="#cite_note-miller-25">[24]</a> is included in <a href="Unicode" title="Unicode">Unicode</a> as U+1F77F.<a href="#cite_note-26">[25]</a> The symbol was designed by Denis Moskowitz, a software engineer in Massachusetts; it is an OR <a href="Monogram" title="Monogram">monogram</a>, designed to resemble both a skull and an <a href="Orca" title="Orca">orca</a>'s gape.<a href="#cite_note-anderson-27">[26]</a> There is a rarer symbol , an inverted <a href="Astrological_symbols" title="Astrological symbols">astrological</a> Pluto symbol, reflecting Orcus as the anti-Pluto: it was designed by Melanie Reinhart.<a href="#cite_note-miller-25">[24]</a>

<div class="mw-heading mw-heading2"><h2 id="Orbit_and_rotation">Orbit and rotation</h2></div>

Orcus is in a 2:3 orbital resonance with <a href="Neptune" title="Neptune">Neptune</a>, having an orbital period of 245 years,<a href="#cite_note-Buie-5">[5]</a><a href="#cite_note-jpldata-1">[1]</a> and is classified as a <a href="Plutino" title="Plutino">plutino</a>.<a href="#cite_note-MPC-Orcus-2">[2]</a> Its orbit is moderately <a href="Orbital_inclination" title="Orbital inclination">inclined</a> at 20.6° to the <a href="Ecliptic" title="Ecliptic">ecliptic</a>.<a href="#cite_note-jpldata-1">[1]</a> Orcus's orbit is similar to Pluto's (both have <a href="Perihelion" class="mw-redirect" title="Perihelion">perihelia</a> above the <a href="Ecliptic" title="Ecliptic">ecliptic</a>), 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 <a href="Angular_separation" class="mw-redirect" title="Angular separation">angular separation</a> of over 60° between them). Over a 14,000-year period, Orcus stays more than 18 AU from Neptune.<a href="#cite_note-MPC2004-D15-19">[18]</a> 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".<a href="#cite_note-MBP-20">[19]</a> Orcus last reached its <a href="Aphelion" class="mw-redirect" title="Aphelion">aphelion</a> (farthest distance from the Sun) in 2019 and will come to perihelion (closest distance to the Sun) around 10 January 2143.<a href="#cite_note-Horizons2143-10">[10]</a> Simulations by the <a href="Deep_Ecliptic_Survey" title="Deep Ecliptic Survey">Deep Ecliptic Survey</a> show that over the next 10 million years Orcus may acquire a perihelion distance (qmin) as small as 27.8 AU.<a href="#cite_note-Buie-5">[5]</a>

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.<a href="#cite_note-Delsanti2010-28">[27]</a> 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 <a href="Rotational_modulation" class="mw-redirect" title="Rotational modulation">rotational modulation</a> of its brightness.<a href="#cite_note-Delsanti2010-28">[27]</a><a href="#cite_note-Ortiz2011-29">[28]</a> Astronomer <a href="Jos%C3%A9_Luis_Ortiz_Moreno" title="José Luis Ortiz Moreno">José Luis Ortiz</a> and colleagues have derived a possible rotation period of about 10.5 hours, assuming that Orcus is not <a href="Tidally_locked" class="mw-redirect" title="Tidally locked">tidally locked</a> with Vanth.<a href="#cite_note-Ortiz2011-29">[28]</a> If, however, the primary is tidally locked with the satellite, the rotational period would coincide with the 9.7-day orbital period of Vanth.<a href="#cite_note-Ortiz2011-29">[28]</a>

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</style><div class="thumb tmulti tleft"><div class="thumbinner multiimageinner" style="width:513px;max-width:513px"><div class="trow"><div class="tsingle" style="width:177px;max-width:177px"><div class="thumbimage"></div><div class="thumbcaption"><a href="Mean-motion_resonance" class="mw-redirect" title="Mean-motion resonance">Mean-motion resonance</a> of Orcus (<a href="Rotating_frame" class="mw-redirect" title="Rotating frame">rotating frame</a> with a period equal to <a href="Neptune" title="Neptune">Neptune</a>'s <a href="Orbital_period" title="Orbital period">orbital period</a>)</div></div><div class="tsingle" style="width:332px;max-width:332px"><div class="thumbimage"></div><div class="thumbcaption">The orbits of Orcus (blue), Pluto (red) and Neptune (grey). Orcus and Pluto are shown in the April 2006 positions. The dates of their <a href="Perihelia" class="mw-redirect" title="Perihelia">perihelia</a> (q) and <a href="Apsis" title="Apsis">aphelia</a> (Q) are also marked.</div></div></div></div></div>

<div class="mw-heading mw-heading2"><h2 id="Physical_characteristics">Physical characteristics</h2></div>

<div class="mw-heading mw-heading3"><h3 id="Size_and_magnitude">Size and magnitude</h3></div>

The absolute magnitude of Orcus is approximately 2.3.<a href="#cite_note-TNOsCool8-12">[12]</a> The detection of Orcus by the <a href="Spitzer_Space_Telescope" title="Spitzer Space Telescope">Spitzer Space Telescope</a> in the <a href="Far_infrared" title="Far infrared">far infrared</a><a href="#cite_note-Stansberry_2007-30">[29]</a> and by <a href="Herschel_Space_Telescope" class="mw-redirect" title="Herschel Space Telescope">Herschel Space Telescope</a> in <a href="Submillimeter" class="mw-redirect" title="Submillimeter">submillimeter</a> estimates its diameter at 958.4 km (595.5 mi), with an uncertainty of 22.9 km (14.2 mi).<a href="#cite_note-TNOsCool8-12">[12]</a> Orcus appears to have an <a href="Albedo#Astronomical_albedo" title="Albedo">albedo</a> of about 21–25%,<a href="#cite_note-TNOsCool8-12">[12]</a> which may be typical of trans-Neptunian objects approaching the 1,000 km (620 mi) diameter range.<a href="#cite_note-tnoalbedo-31">[30]</a> 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.<a href="#cite_note-Brown2010-18">[17]</a> The <a href="Atacama_Large_Millimeter_Array" title="Atacama Large Millimeter Array">ALMA</a> submillimeter measurements taken in 2016 showed that Vanth has a relatively large size of 475 km (295 mi) with an albedo of about 8 percent while Orcus's has a slightly smaller size of 910 km (570 mi).<a href="#cite_note-brown2018-11">[11]</a> Using a <a href="Stellar_occultation" class="mw-redirect" title="Stellar occultation">stellar occultation</a> by Vanth in 2017, Vanth's diameter has been determined to be 442.5 km (275.0 mi), with an uncertainty of 10.2 km (6.3 mi).<a href="#cite_note-Sickafoose2018-32">[31]</a>

<div class="mw-heading mw-heading3"><h3 id="Mass_and_density">Mass and density</h3></div>

Orcus and Vanth are known to constitute a binary system. The mass of the system has been estimated to be (6.348±0.019)×1020 kg,<a href="#cite_note-Grundy-orbits-7">[7]</a> approximately equal to that of the <a href="Saturn" title="Saturn">Saturnian</a> moon <a href="Tethys_(moon)" title="Tethys (moon)">Tethys</a> (6.175×1020 kg).<a href="#cite_note-Jacobson2006-33">[32]</a> The mass of the Orcus system is about 3.8 percent that of <a href="Eris_(dwarf_planet)" title="Eris (dwarf planet)">Eris</a>, the most massive known dwarf planet (1.66×1022 kg).<a href="#cite_note-Brown2010-18">[17]</a><a href="#cite_note-Brown_Schaller_2007-34">[33]</a>

The ratio of the mass of Vanth to that of Orcus was measured astrometrically with the <a href="Atacama_Large_Millimeter_Array" title="Atacama Large Millimeter Array">ALMA</a> submillimeter telescope and is 0.16±0.02 with Vanth containing 13.7%±1.3% of the total system mass. This also means that the densities of both bodies are about the same at ~1.5 g/cm3.<a href="#cite_note-Brown2023-13">[13]</a>

<div class="mw-heading mw-heading3"><h3 id="Spectra_and_surface">Spectra and surface</h3></div>

The first spectroscopic observations in 2004 showed that the visible spectrum of Orcus is flat (neutral in color) and featureless, whereas in the <a href="Near-infrared" class="mw-redirect" title="Near-infrared">near-infrared</a> there were moderately strong <a href="Water_absorption" class="mw-redirect" title="Water absorption">water absorption</a> bands at 1.5 and 2.0 μm.<a href="#cite_note-Fornasier2004-35">[34]</a> 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 <a href="Infrared" title="Infrared">infrared</a> spectra.<a href="#cite_note-Fornasier2004-35">[34]</a> Further infrared observations in 2004 by the <a href="European_Southern_Observatory" title="European Southern Observatory">European Southern Observatory</a> and the <a href="Gemini_telescope" class="mw-redirect" title="Gemini telescope">Gemini telescope</a> gave results consistent with mixtures of water <a href="Ice" title="Ice">ice</a> and <a href="Carbon" title="Carbon">carbonaceous</a> compounds, such as <a href="Tholin" title="Tholin">tholins</a>.<a href="#cite_note-deBergh2005-16">[15]</a> The water and methane ices can cover no more than 50 percent and 30 percent of the surface, respectively.<a href="#cite_note-Trujillo2005-36">[35]</a> This means the proportion of ice on the surface is less than on <a href="Charon_(moon)" title="Charon (moon)">Charon</a>, but similar to that on <a href="Triton_(moon)" title="Triton (moon)">Triton</a>.<a href="#cite_note-Trujillo2005-36">[35]</a>

Later in 2008–2010 new infrared spectroscopic observations with a higher <a href="Signal-to-noise_ratio" title="Signal-to-noise ratio">signal-to-noise ratio</a> revealed additional spectral features. Among them is a deep water ice absorption band at 1.65 μm, which is evidence of the <a href="Crystalline" class="mw-redirect" title="Crystalline">crystalline</a> water ice on the surface of Orcus, and a new absorption band at 2.22 μm. The origin of the latter feature is not completely clear. It can be caused either by <a href="Ammonia" title="Ammonia">ammonia</a>/<a href="Ammonium" title="Ammonium">ammonium</a> dissolved in the water ice or by <a href="Methane" title="Methane">methane</a>/<a href="Ethane" title="Ethane">ethane</a> ices.<a href="#cite_note-Barucci2008-15">[14]</a> The <a href="Radiative_transfer" title="Radiative transfer">radiative transfer</a> modeling showed that a mixture of water ice, tholins (as a darkening agent), ethane ice, and ammonium ion (NH4+) 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.<a href="#cite_note-Delsanti2010-28">[27]</a> 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 <a href="Hydrocarbon" title="Hydrocarbon">hydrocarbons</a> requires a better infrared spectra.<a href="#cite_note-Delsanti2010-28">[27]</a>

Orcus sits at the threshold for trans-Neptunian objects massive enough to retain <a href="Volatile_(astrogeology)" title="Volatile (astrogeology)">volatiles</a> such as methane on the surface.<a href="#cite_note-Delsanti2010-28">[27]</a> The reflectance spectrum of Orcus shows the deepest water-ice absorption bands of any Kuiper belt object that is not associated with the <a href="Haumea_family" title="Haumea family">Haumea collisional family</a>.<a href="#cite_note-Brown2010-18">[17]</a> The <a href="Moons_of_Uranus#Large_moons" title="Moons of Uranus">large icy satellites of Uranus</a> have infrared spectra quite similar to that of Orcus.<a href="#cite_note-Brown2010-18">[17]</a> Among other trans-Neptunian objects, the large plutino <a href="208996_Achlys" title="208996 Achlys">208996 Achlys</a> and Pluto's moon Charon both have similar surface spectra to Orcus,<a href="#cite_note-Barucci2008-15">[14]</a> with flat, featureless visible spectra and moderately strong water ice absorption bands in the near-infrared.<a href="#cite_note-Delsanti2010-28">[27]</a>

<div class="mw-heading mw-heading3"><h3 id="Cryovolcanism">Cryovolcanism</h3></div>

Crystalline water ice on the surfaces of trans-Neptunian objects should be completely <a href="Amorphous_solid" title="Amorphous solid">amorphized</a> by the galactic and Solar radiation in about 10 million years.<a href="#cite_note-Barucci2008-15">[14]</a> Thus the presence of <a href="Crystal" title="Crystal">crystalline</a> water <a href="Ice" title="Ice">ice</a>, and possibly <a href="Ammonia" title="Ammonia">ammonia</a> ice, may indicate that a renewal mechanism was active in the past on the surface of Orcus.<a href="#cite_note-Barucci2008-15">[14]</a> Ammonia so far has not been detected on any trans-Neptunian object or icy satellite of the outer planets other than <a href="Miranda_(moon)" title="Miranda (moon)">Miranda</a>.<a href="#cite_note-Barucci2008-15">[14]</a> The 1.65 <a href="Micrometre" title="Micrometre">μm</a> band on Orcus is broad and deep (12%), as on Charon, <a href="Quaoar" title="Quaoar">Quaoar</a>, <a href="Haumea" title="Haumea">Haumea</a>, and icy satellites of the <a href="Giant_planets" class="mw-redirect" title="Giant planets">giant planets</a>.<a href="#cite_note-Barucci2008-15">[14]</a> Some calculations indicate that <a href="Cryovolcano" title="Cryovolcano">cryovolcanism</a>, which is considered one of the possible renewal mechanisms, may indeed be possible for trans-Neptunian objects larger than about 1,000 km (620 mi).<a href="#cite_note-Delsanti2010-28">[27]</a> 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.<a href="#cite_note-Delsanti2010-28">[27]</a>

<div class="mw-heading mw-heading2"><h2 id="Satellite">Satellite</h2></div>

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</style><div role="note" class="hatnote navigation-not-searchable">Main article: <a href="Vanth_(moon)" title="Vanth (moon)">Vanth (moon)</a></div>

Orcus has one known moon, Vanth (formal designation (90482) Orcus I). It was discovered by <a href="Michael_E._Brown" title="Michael E. Brown">Michael Brown</a> and T.-A. Suer using discovery images taken by the <a href="Hubble_Space_Telescope" title="Hubble Space Telescope">Hubble Space Telescope</a> on 13 November 2005.<a href="#cite_note-IAUC8812-37">[36]</a> The discovery was announced in an <a href="IAU_Circular" title="IAU Circular">IAU Circular</a> notice published on 22 February 2007.<a href="#cite_note-johnston90482-38">[37]</a> A spatially resolved submillimeter imaging of Orcus–Vanth system in 2016 showed that Vanth has a relatively large size of 475 km (295 mi), with an uncertainty of 75 km (47 mi).<a href="#cite_note-brown2018-11">[11]</a> That estimate for Vanth is in good agreement with the size of about 442.5 km (275.0 mi) derived from a <a href="Stellar_occultation" class="mw-redirect" title="Stellar occultation">stellar occultation</a> in 2017.<a href="#cite_note-Sickafoose2018-32">[31]</a> 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 <a href="Dysnomia_(moon)" title="Dysnomia (moon)">Dysnomia</a>. The ratio of masses of Orcus and Vanth is uncertain, possibly anywhere from 1:33 to 1:12.<a href="#cite_note-Carry2011-39">[38]</a>

<ul><li><a href="List_of_possible_dwarf_planets" title="List of possible dwarf planets">List of possible dwarf planets</a></li>

<li><a href="List_of_trans-Neptunian_objects" title="List of trans-Neptunian objects">List of trans-Neptunian objects</a></li>

<li><a href="List_of_Solar_System_objects_by_size" title="List of Solar System objects by size">List of Solar System objects by size</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="Notes">Notes</h2></div>

<li id="cite_note-primary_mass-14"><a href="#cite_ref-primary_mass_14-0">^</a> using the most precise value of Vanth's estimated mass of (8.7±0.8)×1019 kg<a href="#cite_note-Brown2023-13">[13]</a>

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</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2090482">"JPL Small-Body Database Browser: 90482 Orcus (2004 DW)"</a> (2020-01-04 last obs.). Jet Propulsion Laboratory. 29 January 2020. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20190708202911/https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2090482">Archived</a> from the original on 8 July 2019. Retrieved 20 February 2020.</cite>

</li>

<li id="cite_note-MPC-Orcus-2">^ <a href="#cite_ref-MPC-Orcus_2-0">a</a> <a href="#cite_ref-MPC-Orcus_2-1">b</a> <a href="#cite_ref-MPC-Orcus_2-2">c</a> <cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.minorplanetcenter.net/db_search/show_object?object_id=90482">"90482 Orcus (2004 DW)"</a>. Minor Planet Center. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20170403194746/http://www.minorplanetcenter.net/db_search/show_object?object_id=90482">Archived</a> from the original on 3 April 2017. Retrieved 3 April 2017.</cite>

</li>

<li id="cite_note-3"><a href="#cite_ref-3">^</a> <cite class="citation encyclopaedia cs1"><a rel="nofollow" class="external text" href="https://www.dictionary.com/browse/Orcus">"Orcus"</a>. <a href="Dictionary.com" title="Dictionary.com">Dictionary.com Unabridged</a> (Online). n.d.</cite>

</li>

<li id="cite_note-springer-4"><a href="#cite_ref-springer_4-0">^</a> <cite id="CITEREFSchmadel2006" class="citation book cs1">Schmadel, Lutz D. (2006). "(90482) Orcus [39.5, 0.22, 20.5]". Dictionary of Minor Planet Names. Springer Berlin Heidelberg. p. 236. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1007%2F978-3-540-34361-5_2818">10.1007/978-3-540-34361-5_2818</a>. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-3-540-34361-5</bdi>.</cite>

</li>

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<li id="cite_note-Jacobson2006-33"><a href="#cite_ref-Jacobson2006_33-0">^</a> <cite id="CITEREFJacobsonAntreasianBordiCriddle2006" class="citation journal cs1">Jacobson, R. A.; Antreasian, P. G.; Bordi, J. J.; Criddle, K. E.; Ionasescu, R.; Jones, J. B.; Mackenzie, R. A.; Meek, M. C.; Parcher, D.; Pelletier, F. J.; Owen, Jr., W. M.; Roth, D. C.; Roundhill, I. M.; Stauch, J. R. (December 2006). <a rel="nofollow" class="external text" href="https://doi.org/10.1086%2F508812">"The Gravity Field of the Saturnian System from Satellite Observations and Spacecraft Tracking Data"</a>. The Astronomical Journal. 132 (6): 2520–2526. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2006AJ....132.2520J">2006AJ....132.2520J</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1086%2F508812">10.1086/508812</a>.</cite>

</li>

<li id="cite_note-Brown_Schaller_2007-34"><a href="#cite_ref-Brown_Schaller_2007_34-0">^</a> <cite id="CITEREFBrownSchaller2007" class="citation journal cs1"><a href="Michael_E._Brown" title="Michael E. Brown">Brown, Michael E.</a>; Schaller, Emily L. (15 June 2007). <a rel="nofollow" class="external text" href="https://web.archive.org/web/20160304053122/http://hubblesite.org/pubinfo/pdf/2007/24/pdf.pdf">"The Mass of Dwarf Planet Eris"</a> (PDF). Science. 316 (5831): 1585. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2007Sci...316.1585B">2007Sci...316.1585B</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1126%2Fscience.1139415">10.1126/science.1139415</a>. <a href="PMID_(identifier)" class="mw-redirect" title="PMID (identifier)">PMID</a> <a rel="nofollow" class="external text" href="https://pubmed.ncbi.nlm.nih.gov/17569855">17569855</a>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:21468196">21468196</a>. Archived from <a rel="nofollow" class="external text" href="http://hubblesite.org/pubinfo/pdf/2007/24/pdf.pdf">the original</a> (PDF) on 4 March 2016.</cite>

</li>

<cite id="CITEREFFornasierDotto,_E.Barucci,_M.A.Barbieri,_C.2004" class="citation journal cs1">Fornasier, S.; Dotto, E.; Barucci, M.A.; Barbieri, C. (2004). <a rel="nofollow" class="external text" href="https://doi.org/10.1051%2F0004-6361%3A20048004">"Water ice on the surface of the large TNO 2004 DW"</a>. Astronomy & Astrophysics. 422 (2): L43 – L46. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2004A&A...422L..43F">2004A&A...422L..43F</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1051%2F0004-6361%3A20048004">10.1051/0004-6361:20048004</a>.</cite>

</li>

<cite id="CITEREFTrujilloBrownRabinowitzGeballe2005" class="citation journal cs1"><a href="Chad_Trujillo" title="Chad Trujillo">Trujillo, Chadwick A.</a>; <a href="Michael_E._Brown" title="Michael E. Brown">Brown, Michael E.</a>; <a href="David_L._Rabinowitz" title="David L. Rabinowitz">Rabinowitz, David L.</a>; Geballe, Thomas R. (2005). "Near-Infrared Surface Properties of the Two Intrinsically Brightest Minor Planets: (90377) Sedna and (90482) Orcus". The Astrophysical Journal. 627 (2): 1057–1065. <a href="ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<a rel="nofollow" class="external text" href="https://arxiv.org/abs/astro-ph/0504280">astro-ph/0504280</a>. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2005ApJ...627.1057T">2005ApJ...627.1057T</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1086%2F430337">10.1086/430337</a>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:9149700">9149700</a>.</cite>

</li>

<li id="cite_note-IAUC8812-37"><a href="#cite_ref-IAUC8812_37-0">^</a> <cite id="CITEREFDaniel_W._E._Green2007" class="citation web cs1">Daniel W. E. Green (22 February 2007). <a rel="nofollow" class="external text" href="http://www.cbat.eps.harvard.edu/iauc/08800/08812.html">"IAUC 8812: Sats OF 2003 AZ_84, (50000), (55637), (90482)"</a>. International Astronomical Union Circular. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20110719205520/http://cbat.eps.harvard.edu/iauc/08800/08812.html">Archived</a> from the original on 19 July 2011. Retrieved 4 July 2011.</cite>

</li>

<li id="cite_note-johnston90482-38"><a href="#cite_ref-johnston90482_38-0">^</a> <cite id="CITEREFWm._Robert_Johnston2007" class="citation web cs1">Wm. Robert Johnston (4 March 2007). <a rel="nofollow" class="external text" href="http://www.johnstonsarchive.net/astro/astmoons/am-90482.html">"(90482) Orcus"</a>. Johnston's Archive. <a rel="nofollow" class="external text" href="https://web.archive.org/web/20090210205551/http://www.johnstonsarchive.net/astro/astmoons/am-90482.html">Archived</a> from the original on 10 February 2009. Retrieved 26 March 2009.</cite>

</li>

<li id="cite_note-Carry2011-39"><a href="#cite_ref-Carry2011_39-0">^</a> <cite id="CITEREFCarry2011" class="citation journal cs1">Carry, B.; Hestroffer, D.; Demeo, F. E.; Thirouin, A.; Berthier, J.; Lacerda, P.; Sicardy, B.; Doressoundiram, A.; Dumas, C.; Farrelly, D.; Müller, T. G. (2011). "Integral-field spectroscopy of (90482) Orcus–Vanth". Astronomy & Astrophysics. 534: A115. <a href="ArXiv_(identifier)" class="mw-redirect" title="ArXiv (identifier)">arXiv</a>:<a rel="nofollow" class="external text" href="https://arxiv.org/abs/1108.5963">1108.5963</a>. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/2011A&A...534A.115C">2011A&A...534A.115C</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1051%2F0004-6361%2F201117486">10.1051/0004-6361/201117486</a>. <a href="S2CID_(identifier)" class="mw-redirect" title="S2CID (identifier)">S2CID</a> <a rel="nofollow" class="external text" href="https://api.semanticscholar.org/CorpusID:118524500">118524500</a>.</cite>

</li>

</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

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<div class="side-box-text plainlist">Wikimedia Commons has media related to <a href="https://commons.wikimedia.org/wiki/Category:90482_Orcus" class="extiw external" title="commons:Category:90482 Orcus">90482 Orcus</a>.</div></div>

</div>

<ul><li><a rel="nofollow" class="external text" href="http://www.minorplanetcenter.net/mpec/K04/K04D09.html">MPEC 2004-D09</a> announcing the discovery but attributing it to Raymond J. Bambery, Steven H. Pravdo, Michael D. Hicks, <a href="Kenneth_J._Lawrence" title="Kenneth J. Lawrence">Kenneth J. Lawrence</a>, Daniel MacDonald, <a href="Eleanor_Helin" class="mw-redirect" title="Eleanor Helin">Eleanor Helin</a> and Robert Thicksten / <a href="Near-Earth_Asteroid_Tracking" title="Near-Earth Asteroid Tracking">NEAT</a></li>

<li><a rel="nofollow" class="external text" href="http://www.minorplanetcenter.net/mpec/K04/K04D13.html">MPEC 2004-D13</a> correcting MPEC 2004-D09</li>

<li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20070322195011/http://www.chadtrujillo.com/2004dw/">Chad Trujillo's page on 2004 DW</a></li>

<li><a rel="nofollow" class="external text" href="https://apod.nasa.gov/apod/ap090325.html">Orcus of the Outer Solar System</a>, <a href="Astronomy_Picture_of_the_Day" title="Astronomy Picture of the Day">Astronomy Picture of the Day</a>, 25 March 2009</li>

<li><a rel="nofollow" class="external text" href="http://news.bbc.co.uk/2/hi/science/nature/3506329.stm">New world found far beyond Pluto</a>, David Whitehouse, BBC News, 3 March 2004</li>

<li><a rel="nofollow" class="external text" href="https://skyandtelescope.org/astronomy-news/a-new-kuiper-belt-giant/">A New Kuiper Belt Giant</a>, Stuart Goldman, Sky & Telescope, 24 February 2004</li>

<li><a rel="nofollow" class="external text" href="https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=90482">Orcus</a> at the <a href="JPL_Small-Body_Database" title="JPL Small-Body Database">JPL Small-Body Database</a></li></ul>

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</style><div id="Minor_planets_navigator60" style="font-size:114%;margin:0 4em"><a href="List_of_minor_planets#Main_index" title="List of minor planets">Minor planets navigator</a></div></th></tr><tr><td colspan="2" class="navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="90481_Wollstonecraft" class="mw-redirect" title="90481 Wollstonecraft">90481 Wollstonecraft </a></li>

<li><a href="List_of_minor_planets%3A_90001%E2%80%9391000#482" title="List of minor planets: 90001–91000">90482 Orcus</a></li></ul>

</div></td></tr></tbody></table></div>

<div class="navbox-styles"></div><div role="navigation" class="navbox" aria-labelledby="Dwarf_planets437" style="padding:3px"><table class="nowraplinks hlist mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="3" style="text-align: center;"><div id="Dwarf_planets437" style="font-size:114%;margin:0 4em"><a href="Dwarf_planet" title="Dwarf planet">Dwarf planets</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="3" style="text-align: center;"><div>

<ul><li><a href="List_of_possible_dwarf_planets" title="List of possible dwarf planets">List of possible dwarf planets</a></li>

<li><a href="List_of_Solar_System_objects_by_size" title="List of Solar System objects by size">List of Solar System objects by size</a></li>

<li>Former dwarf planets

<ul><li><a href="Phoebe_(moon)" title="Phoebe (moon)">Phoebe</a></li>

<li><a href="Triton_(moon)" title="Triton (moon)">Triton</a></li>

<li><a href="4_Vesta" title="4 Vesta">Vesta</a></li>

<li><a href="2_Pallas" title="2 Pallas">Pallas</a></li></ul></li>

<li><a href="Mesoplanet" title="Mesoplanet">Mesoplanet</a></li>

<li><a href="Planemo" class="mw-redirect" title="Planemo">Planemo</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Consensus</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Ceres_(dwarf_planet)" title="Ceres (dwarf planet)">Ceres</a>

<ul><li><a href="Geology_of_Ceres" title="Geology of Ceres">Geology</a></li>

<li><a href="Ceres_(dwarf_planet)#Atmosphere" title="Ceres (dwarf planet)">Atmosphere</a></li></ul></li>

<li>

<li><a href="Pluto" title="Pluto">Pluto</a>

<ul><li><a href="Geology_of_Pluto" title="Geology of Pluto">Geology</a></li>

<li><a href="Atmosphere_of_Pluto" title="Atmosphere of Pluto">Atmosphere</a></li>

<li><a href="Moons_of_Pluto" title="Moons of Pluto">Moons</a></li></ul></li>

<li><a href="Haumea" title="Haumea">Haumea</a>

<ul><li><a href="Moons_of_Haumea" title="Moons of Haumea">Moons</a></li>

<li><a href="Makemake" title="Makemake">Makemake</a>

<li><a href="Quaoar" title="Quaoar">Quaoar</a>

<li><a href="Quaoar#Rings" title="Quaoar">Rings</a></li></ul></li>

<li><a href="Gonggong_(dwarf_planet)" title="Gonggong (dwarf planet)">Gonggong</a>

<li><a href="Sedna_(dwarf_planet)" title="Sedna (dwarf planet)">Sedna</a></li></ul>

</div></td><td class="noviewer navbox-image" rowspan="2" style="width:1px;padding:0 0 0 2px;padding-left: 0.5em;"><div> </div></td></tr><tr><th scope="row" class="navbox-group" style="text-align: center;;width:1%">Candidate (for TNOs, D+1σ ≥ 700 km or H ≤ 4.2)</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Asteroid" title="Asteroid">Asteroids</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="10_Hygiea" title="10 Hygiea">Hygiea</a></li>

<li><a href="704_Interamnia" title="704 Interamnia">Interamnia</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Plutino" title="Plutino">Plutinos</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="28978_Ixion" title="28978 Ixion">Ixion</a></li>

<li><a href="208996_Achlys" title="208996 Achlys">Achlys</a>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Classical_Kuiper_belt_object" title="Classical Kuiper belt object">Cubewanos</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="120347_Salacia" title="120347 Salacia">Salacia</a>

<ul><li><a href="Actaea_(moon)" title="Actaea (moon)">Actaea</a></li></ul></li>

<li><a href="174567_Varda" title="174567 Varda">Varda</a>

<ul><li><a href="Ilmar%C3%AB" title="Ilmarë">Ilmarë</a></li></ul></li>

<li><a href="145452_Ritona" title="145452 Ritona">Ritona</a></li>

<li><a href="20000_Varuna" title="20000 Varuna">Varuna</a>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Scattered_disc" title="Scattered disc">Scattered disc objects</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

<li>Chiminigagua

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Detached_object" title="Detached object">Detached objects</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em">

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%"><a href="Sednoid" title="Sednoid">Sednoids</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em">

</div></td></tr></tbody></table><div></div></td></tr><tr><td class="navbox-abovebelow" colspan="3" style="text-align: center;"><div>

<ul><li> Category</li></ul>

</div></td></tr></tbody></table></div>

<div class="navbox-styles"></div><div role="navigation" class="navbox" aria-labelledby="Trans-Neptunian_objects103" style="padding:3px"><table class="nowraplinks mw-collapsible autocollapse navbox-inner" style="border-spacing:0;background:transparent;color:inherit"><tbody><tr><th scope="col" class="navbox-title" colspan="2"><div id="Trans-Neptunian_objects103" style="font-size:114%;margin:0 4em"><a href="Trans-Neptunian_object" title="Trans-Neptunian object">Trans-Neptunian objects</a></div></th></tr><tr><th scope="row" class="navbox-group" style="width:1%;white-space: normal; text-align:center;">TNO classes</th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Classical_Kuiper_belt_object" title="Classical Kuiper belt object">Cubewanos</a></li>

<li><a href="Scattered_disc" title="Scattered disc">Scattered-disc objects</a></li>

<li><a href="Detached_object" title="Detached object">Detached objects</a></li>

<li><a href="Resonant_trans-Neptunian_object" title="Resonant trans-Neptunian object">Resonant objects</a>

<ul><li><a href="Neptune_trojan" title="Neptune trojan">Neptune trojans</a></li>

<li><a href="Plutino" title="Plutino">Plutinos</a></li>

<li><a href="Resonant_trans-Neptunian_object#1:2_resonance_("twotinos",_period_~330_years)" title="Resonant trans-Neptunian object">Twotinos</a></li></ul></li>

<li><a href="Minor-planet_moon#Trans-Neptunian_objects" title="Minor-planet moon">TNO moons</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;white-space: normal; text-align:center;"><a href="Dwarf_planet" title="Dwarf planet">Dwarf planets</a> (moons)</th><td class="navbox-list-with-group navbox-list navbox-even hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="Vanth_(moon)" title="Vanth (moon)">Vanth</a></li></ul></li>

<li><a href="Pluto" title="Pluto">Pluto</a>

<ul><li><a href="Charon_(moon)" title="Charon (moon)">Charon</a></li>

<li><a href="Kerberos_(moon)" title="Kerberos (moon)">Kerberos</a></li>

<li><a href="Hydra_(moon)" title="Hydra (moon)">Hydra</a></li></ul></li>

<li><a href="Haumea" title="Haumea">Haumea</a>

<ul><li><a href="Namaka_(moon)" title="Namaka (moon)">Namaka</a></li>

<li><a href="Hi%CA%BBiaka_(moon)" title="Hiʻiaka (moon)">Hiʻiaka</a></li>

<li><a href="Quaoar" title="Quaoar">Quaoar</a>

<ul><li><a href="Weywot_(moon)" class="mw-redirect" title="Weywot (moon)">Weywot</a></li>

<li><a href="50000_Quaoar" class="mw-redirect" title="50000 Quaoar">Rings</a></li></ul></li>

<li><a href="Makemake" title="Makemake">Makemake</a>

<li><a href="Gonggong_(dwarf_planet)" title="Gonggong (dwarf planet)">Gonggong</a>

<ul><li><a href="Xiangliu_(moon)" title="Xiangliu (moon)">Xiangliu</a></li></ul></li>

<ul><li><a href="Dysnomia_(moon)" title="Dysnomia (moon)">Dysnomia</a></li></ul></li>

<li><a href="Sedna_(dwarf_planet)" title="Sedna (dwarf planet)">Sedna</a></li></ul>

</div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;white-space: normal; text-align:center;"><a href="Sednoid" title="Sednoid">Sednoids</a></th><td class="navbox-list-with-group navbox-list navbox-odd hlist" style="width:100%;padding:0"><div style="padding:0 0.25em">

<ul><li><a href="90377_Sedna" class="mw-redirect" title="90377 Sedna">90377 Sedna</a></li>

<li><a href="541132_Lele%C4%81k%C5%ABhonua" title="541132 Leleākūhonua">541132 Leleākūhonua</a></li>

</div></td></tr></tbody></table></div>

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