90482 Orcus Etruscan equivalent of the Roman Pluto, and later became an alternate name for Pluto. The surface of Orcus is relatively bright with albedo reaching 23%, grey in color and water-rich. 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. The existence of a satellite allowed astronomers to determine the mass of the system, which is approximately equal to that of the Saturnian moon Tethys. The ratio of masses of Orcus and Vanth is uncertain, possibly anywhere from 1:33 to 1:12. The diameter of Orcus
90482 Orcus relatively large satellite (Vanth, see below) may change them considerably. The absolute magnitude of Vanth is estimated at 4.88, which means that it is about 11 times fainter than Orcus itself. If the albedos of both bodies are the same at 0.23 then the size of Orcus is about , and the size of Vanth is about . The ALMA submillimeter measurements taken in 2016 showed that Vanth has a relatively large size of with albedo of about 8% while Orcus' has a slightly smaller size of 910 km. Using a stellar occultation by Vanth in 2017, Vanth's diameter has