| Deep Ecliptic Survey|
| 18 November 1998|
4784 days (13.10 yr)
1998 WW31 Wikipedia
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.