[8] Compared to Orcus, Vanth has a darker and slightly redder surface that supposedly lacks exposed water ice, resembling primordial Kuiper belt objects.

[4][d] On 23 March 2009, Brown asked readers of his blog to suggest possible names for the satellite, with the best one to be submitted to the International Astronomical Union (IAU) on 5 April.

[17][18] Vanth and Persipnei were among the few names that both matched the Etruscan origin and chthonic theme of Orcus's name, though Brown ultimately chose Vanth because its relationship to Orcus in Etruscan mythology strongly parallels the relationship between Pluto and Charon in Greek mythology.

[17] In Etruscan iconography, Vanth is frequently portrayed in the company of Charun (the Etruscan counterpart of the Greek Charon), which alludes to the similar properties of the Pluto and Orcus systems (the latter being nicknamed the "anti-Pluto" because the orbital resonance with Neptune keeps it on the opposite side of the Sun from Pluto).

Orcus and Vanth are separated 9,000 km (5,600 mi) apart from each other's centers and revolve around their barycenter in nearly circular orbits with a period of 9.54 days.

[23]: 804, 806  Earlier calculations by Michael Brown et al. in 2010 suggested that it took 150–400 million years for both components of the Orcus–Vanth system to migrate out to their current separation distance and become tidally locked.

[11]: 2704 An impact origin of the Orcus and Vanth system would imply that both components should have similar densities, surface compositions, and colors.

[11]: 2702  While Vanth does have a similar density to Orcus (albeit with large uncertainty),[8]: 5  Vanth appears redder and tentative spectroscopic studies have suggested that it has low amounts of exposed water ice, which may make it resemble primordial Kuiper belt objects more than Orcus, whose surface has a neutral (gray) color and is abundant in exposed water ice by contrast.

[20]: 5  However, these alternative hypotheses have since fallen out of favor as Vanth's physical properties and formation mechanisms of dwarf planet satellites became better understood.

[7]: 1 [8] As of 2023[update], the most accurate estimate for Vanth's diameter is 443 ± 10 km (275 ± 6 mi), determined from a stellar occultation in 2017.

[6]: 664 [7]: 2  Both estimates show that Vanth is roughly half of Orcus's diameter and is the third-largest known moon of a trans-Neptunian object, after Charon and Dysnomia.

[8]: 5 Visible and near-infrared Hubble observations of Vanth from 2007 to 2008 showed that the moon's surface appears moderately red, being increasingly more reflective over longer and redder wavelengths.

[11]: 2702 [20]: 5  Vanth's reddish color and apparent lack of exposed water ice hinted that it should have a dark surface with a geometric albedo lower than that of Orcus;[11]: 2704 [9]: 6  this was confirmed in ALMA observations from 2016, which determined a geometric albedo of 0.08 for Vanth based on its thermal emission.

[9]: 2  Continuous photometric observations of the unresolved Orcus–Vanth system in 2009–2010 showed that its overall brightness varies with a small light curve amplitude of 0.06±0.04 magnitudes and a period of 9.7±0.3 days.