Editing Orcus (dwarf planet) (section)

== 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" />