90482 Orcus

90482 Orcus (symbol: ), originally known by the provisional designation 2004 DW, is a Kuiper belt object (KBO). It is also a dwarf planet. It was found by Michael Brown, Chad Trujillo and David Rabinowitz on February 17, 2004. It was also seen in pictures from November 8, 1951. Like Pluto it is in orbital resonance with Neptune but it stays on the opposite side of the Sun from Pluto.

90482 Orcus

Discovery
Discovered by	M. Brown, C. Trujillo, D. Rabinowitz
Discovery date	February 17, 2004
Designations
Alternative names	2004 DW
Minor planet category	Plutino Dwarf planet Plutoid TNO KBO[1]
Orbital characteristics
Epoch November 30, 2008 (JD 2 454 800)
Aphelion	7 188.17 Gm (48.05 AU)
Perihelion	4 535.80 Gm (30.32 AU)
Semi-major axis	5 862.44 Gm (39.188 AU)
Eccentricity	0.226 18
Orbital period	89 606 d (245.33 yr)
Average orbital speed	4.68 km/s
Mean anomaly	164.68°
Inclination	20.593°
Longitude of ascending node	268.722°
Argument of perihelion	72.474°
Known satellites	1 (92-432 km)
Physical characteristics
Dimensions	946.3 +74.1 −72.3 km (diameter)[2]
Mass	~7.5×1020 kg
Mean density	~1.5 g/cm³ (assumed)
Surface gravity	~0.2 m/s²
Escape velocity	~0.44 km/s
Rotation period	13.19h[3]
Albedo	19.75 +3.40 −2.76 %
Temperature	~45 K
Spectral type	B-V=0.68; V-R=0.37 [4]
Apparent magnitude	19.1 (opposition)[5]
Absolute magnitude (H)	2.3[6]

Moon

A moon of Orcus was found on 22 February 2007.^[7]

The satellite was found at 0.25 arcsec from Orcus with magnitude difference of 2.7.^[8] Assuming an albedo similar to that of the primary, the magnitude suggests a diameter of about 220 km. It is thought to be a smaller KBO that was captured.

Other websites

• MPEC 2004-D09 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 correcting MPEC 2004-D09
• Chad Trujillo's page on 2004 DW Archived 2007-03-22 at the Wayback Machine
• First BBC article
• First New Scientist article
• Updated orbital elements from Lowell Observatory Archived 2007-05-22 at the Wayback Machine
• AstDys orbital elements
• Orbital simulation from JPL (Java) / Ephemeris