Orcus
Orcus is a dwarf planet locked in the same 3:2 orbital resonance with Neptune as Pluto, but always on the opposite side of its orbit — earning it the nickname 'anti-Pluto'. It has a large moon, Vanth. No spacecraft has visited.
Key facts
Science
Physical
- Mass
- 6.30 × 10²⁰ kg · 0.00858 Moon masses
- Radius
- 460 km · 7% of Earth's radius
- Density
- 1,545 kg/m³ · 1.5× water
- Surface gravity
- 0.199 m/s² · 2% of Earth's
- Escape velocity
- 428 m/s · 4% of Earth's
Orbital
- Distance from the Sun
- 48 AU
- Semi-major axis
- 39.4 AU
- Eccentricity
- 0.2203
- Inclination
- 30.35 °
- Orbital period
- 247.19 years
- Perihelion
- 30.7 AU
- Aphelion
- 48.1 AU
- Mean orbital velocity
- 4.75 km/s
Rotation
- Rotation period
- 13.19 hours
Composition
- Bulk composition
- Spectroscopy shows crystalline water ice and probably ammonia on a fairly neutral-coloured surface; both are slowly destroyed by radiation, hinting at relatively recent cryovolcanic resurfacing. The deep interior is unconstrained — no spacecraft has visited.
- Surface imagery
- No real surface imagery exists — this object has never been visited; color is approximate, inferred from spectroscopy.
Radiation & temperature
- Insolation
- 0.000645 S⊕ · 1/1,551 of the sunlight Earth receives
- Geometric albedo
- 0.23
- Equilibrium temperature
- 42 K (-232 °C)
Discovery & history
- Discovered
- February 17, 2004
- By
- Mike Brown, Chad Trujillo and David Rabinowitz
- Method
- Photographic plates
- Name
- Orcus, a god of the underworld in Etruscan and Roman myth — a deliberate counterpart to Pluto, whose orbit Orcus mirrors; its moon Vanth is an Etruscan underworld spirit.
Orcus was discovered on 17 February 2004 by Mike Brown, Chad Trujillo and David Rabinowitz (provisional designation 2004 DW). It follows the same 3:2 resonance with Neptune as Pluto, but always sits at the opposite point of its orbit — earning it the nickname the 'anti-Pluto', which guided its naming after Orcus, another god of the underworld. Its surface shows crystalline water ice and probably ammonia, which radiation should slowly destroy, hinting at relatively recent cryovolcanic resurfacing. A large moon, Vanth, was discovered in 2005.
Images
Images from open archives · credit shown per image