1998 WW31

Orbit and classification

Located beyond the orbit of Neptune, is a non-resonant classical Kuiper belt object (cubewano) of the so-called hot population, which have higher inclinations than those of the cold population. It orbits the Sun at a distance of 40.4–48.5 AU once every 297 years (108,345 days; semi-major axis of 44.48 AU). Its orbit has an eccentricity of 0.09 and an inclination of 7° with respect to the ecliptic. The body's observation arc begins at Kitt Peak with its first observation on 18 November 1998.

Numbering and naming

As of 2025, this minor planet has not been numbered nor named by the Minor Planet Center.

Physical characteristics

is expected to have a low albedo due to its blue (neutral) color. Other sources assume a higher albedo of 0.10 and 0.16, respectively (see below). It has a V–I color index of 0.91, notably lower than the mean-color index for cubewanos, and in between that of comets and Jupiter trojans.

Satellite

On 22 December 2000, French astronomers Christian Veillet and Alain Doressoundiram in collaboration with J. Shapiro discovered the satellite using the Canada–France–Hawaii Telescope at Mauna Kea on the Big Island of Hawaii, United States. The discovery was announced on 16 April 2001, and received the provisional designation S/2000 () 1.

It was the first trans-Neptunian binary discovered after Charon in 1978, the largest satellite in the Pluto–Charon system. Since then many trans-Neptunian binaries have been discovered. is also one of the most symmetrical binaries known in the Solar System.

The satellite has a highly eccentric orbit with an eccentricity of with an exceptionally long orbital period of and a semi-major axis of .

Diameter and albedo

While the primary measures 148 km, the satellite has a diameter of 123 km (a ratio of 0.883) with a combined system diameter of 192 km. The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.10 and calculates a system diameter of 192 km based on an absolute magnitude of 6.7, while Mike Brown finds a diameter of 267 km with a lower albedo of 0.04.

Rotation period

As of 2020, no rotational lightcurve of has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.

References

• The binary Kuiper-belt object , publication in Nature, 18 April 2002
• The binary Kuiper Belt Object 1998 WW31, Christian Veillet - CFHT - 17 April 2002
• IAUC 7610: S/2000 (1998 WW_31) 1, satellite discovery – Central Bureau for Astronomical Telegrams, 16 April 2001
• Orbit Fit and Astrometric record for 1998 WW31, Marc W. Buie, SwRI (Space Science Department)
• and S/2000 () 1
• MPEC 2008-O05 : Distant Minor Planets (2008 AUG. 2.0 TT)

References

1. (December 2019). "Mutual orbit orientations of transneptunian binaries". Icarus.