90482 Orcus

Discovery
Discoverer	M. Brown, C. Trujillo, D. Rabinowitz
Discovery Date	February 17, 2004
Alternate Designations	2004 DW
Category	Plutino
Orbital Elements Epoch October 22, 2004 (JD 2453300.5)
Eccentricity (e)	0.218
Semi-Major Axis (a)	5903.997 Gm (39.466 AU)
Perihelion (q)	4616.704 Gm (30.861 AU)
Aphelion (Q)	7191.291 Gm (48.071 AU)
Orbital Period (P)	90558.570 d (247.94 a)
Mean Orbital Speed	4.68 km/s
Inclination (i)	20.559°
Longitude of the Ascending Node (Ω)	268.556°
Argument of Perihelion (ω)	73.231°
Mean Anomaly (M)	158.056°
Physical Characteristics
Dimensions	840 - 1880 km
Mass	6.2 - 70×1020 kg
Density	2.0? g/cm³
Surface Gravity	0.2348 - 0.5254 m/s²
Escape Velocity	0.4441 - 0.9939 km/s
Rotation Period	? d
Spectral Class	?
Absolute Magnitude	2.3
Albedo	0.09
Mean Surface Temperature	~61 K

90482 Orcus is a Kuiper Belt object (KBO) that was discovered by Michael (Mike) E. Brown of Caltech, Chadwick (Chad) A. Trujillo of the Gemini Observatory, and David L. Rabinowitz of Yale University. The image of this object was first acquired on February 17, 2004.

Size and magnitude

The apparent magnitude of the object is 18.5, which is the same brightness as 50000 Quaoar. The orbit indicates that the object is a Plutino. Therefore, the object is probably larger than Quaoar, since it is farther from the Sun. Using an assumed albedo of 0.09, Trujillo estimates its diameter to be approximately 1600 km, which makes Orcus potentially the second-largest KBO, after Pluto. (The recently discovered 90377 Sedna, lying beyond the Kuiper Belt, may be the second-largest TNO).

Name

Since it shares a similar size and orbit to that of Pluto, it too must be named after a deity of the underworld. In accordance with IAU rules, the discoverers' suggested name of Orcus was approved and published November 22, 2004. Orcus is both another name for the Greek deity Hades and a separate god of the dead in Roman mythology.

External links and sources

• MPEC 2004-D09 (http://cfa-www.harvard.edu/mpec/K04/K04D09.html) announcing the discovery but attributing it to Raymond J. Bambery, Steven H. Pravdo, Michael D. Hicks, Kenneth J. Lawrence, Daniel MacDonald, Eleanor F. Helin and Robert Thicksten / NEAT
• MPEC 2004-D13 (http://cfa-www.harvard.edu/mpec/K04/K04D13.html) correcting MPEC 2004-D09
• C. Trujillo's page on 2004 DW (http://www.gps.caltech.edu/~chad/2004dw/)
• First BBC article (http://news.bbc.co.uk/2/hi/science/nature/3506329.stm)
• First New Scientist article (http://www.newscientist.com/news/news.jsp?id=ns99994702)

The Minor Planets

Vulcanoids | Main belt | Groups and Families | Near-Earth objects | Jupiter Trojans

Centaurs | Trans-Neptunians | Damocloids | Comets | Kuiper Belt | Oort Cloud

(For other objects and regions, see: Binary asteroids, Asteroid moons and the Solar system)

(For a complete listing, see: List of asteroids)

cs:Orcus (planetka) da:2004 DW de:2004 DW fr:90482 Orcus it:2004 DW nl:2004 DW