1998 WW31

1998 WW₃₁

Artist's Impression of 1998 WW31
Discovery
Discovered by	Deep Ecliptic Survey
Discovery date	18 November 1998
Designations
MPC designation	1998 WW31
Alternate name(s)	none
Minor planet category	Trans-Neptunian object
Orbital characteristics
Epoch June 14, 2006 (JD 2453900.5)
Aphelion	48.419 AU (7243.350 Gm)
Perihelion	40.559 AU (6067.553 Gm)
Semi-major axis	44.489 AU (6655.451 Gm)
Eccentricity	0.088
Orbital period	296.75 a (108386.849 d)
Average orbital speed	4.46 km/s
Mean anomaly	126.983°
Inclination	6.818°
Longitude of ascending node	237.108°
Argument of perihelion	49.588°
Satellites	1
Proper orbital elements
Physical characteristics
Dimensions	133±15 km
Mass	1.3–2.5×1018 kg (system)
Mean density	1.5 g/cm³ (assumed)
Equatorial surface gravity	0.025–0.031 m/s²
Escape velocity	0.054–0.068 km/s
Sidereal rotation period	570 d (system orbital period)
Albedo	0.05–0.09 (assumed)
Temperature	~42 K
Absolute magnitude (H)	6.05

1998 WW₃₁ (also written 1998 WW31) is a double Kuiper belt object. It was discovered in 1998 by the Deep Ecliptic Survey (DES).

1998 WW₃₁ forms a binary system with another object with the IAU provisional designation S/2000 (1998 WW₃₁) 1: the first trans-Neptunian binary to be discovered since Pluto, and one of the most symmetrical binaries known in the Solar System. The two bodies are very close in size, with a diameter ratio of 1.2 and a mass ratio of 1.74, assuming similar surfaces and densities. Their orbital period is approximately 570 days, and they orbit at a distance of approximately 4000 km (closest approach) to 40,000 km, with a semi-major axis of about 22,000 km. Their diameters are likely to be in the 100–150 km range, assuming a density of 1–2 g/cm³. Their combined mass is 1/6000th that of the Pluto–Charon system.

External links

• The IAU circular announcing the discovery of the companion
• 1998 WW₃₁ and S/2000 (1998 WW31) 1
• Discussion at CFHT, Hawaii