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 with the normal object naming procedures. Vanth was found at 0.25 arcsec from Orcus with magnitude difference of . Estimates made in 2009 by Mike Brown show that the apparent magnitude of Vanth is which is magnitudes fainter than Orcus. Assuming equal albedos this would mean a diameter of 280 km, or 2.9 times smaller than the primary. However, the dissimilar colors of Orcus (neutral) and Vanth (red) suggest that Vanth could have an albedo a factor of two lower than Orcus. Should Vanth have an albedo of only 0.12, Vanth could be as large as 380 km with Orcus