1998 WW31

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1998 WW31
Artist's impression of 1998 WW31.jpg
Artist's Impression of 1998 WW31 and its satellite
Discovered by Deep Ecliptic Survey
Discovery date 18 November 1998
MPC designation 1998 WW31
Orbital characteristics[1]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 4
Observation arc 4784 days (13.10 yr)
Aphelion 48.432 AU (7.2453 Tm)
Perihelion 40.847 AU (6.1106 Tm)
44.640 AU (6.6780 Tm)
Eccentricity 0.084953
298.26 yr (108938 d)
4.46 km/s
0° 0m 11.897s /day
Inclination 6.8069°
Known satellites 1
Earth MOID 39.8336 AU (5.95902 Tm)
Jupiter MOID 35.6694 AU (5.33607 Tm)
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
Equatorial escape velocity
0.054–0.068 km/s
570 d (system orbital period)
0.05–0.09 (assumed)
Temperature ~42 K

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 Charon, 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.


  1. ^ a b "JPL Small-Body Database Browser: (1998 WW31)". Jet Propulsion Laboratory. Retrieved 29 March 2016. 

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