Editing Orcus (dwarf planet) (section)

=== 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"/>