| Minorplanet: | yes |
| Background: |
|
| Discovered: | 18 November 1998 |
| Epoch: | 31 May 2020 (JD 2459000.5) |
| Uncertainty: | 4 |
| Observation Arc: | 20.94 yr (7,647 d) |
| Perihelion: | 40.429 AU |
| Semimajor: | 44.477 AU |
| Eccentricity: | 0.09102 |
| Period: | 296.63 yr (108,345 d) |
| Mean Motion: | / day |
| Inclination: | 6.8171° |
| Asc Node: | 237.138° |
| Arg Peri: | 51.218° |
| Satellites: | 1 |
| Mean Diameter: | |
| Albedo: | 0.04 |
| Abs Magnitude: | 6.7 6.9 |
, is a non-resonant trans-Neptunian object and binary system from the Kuiper belt located in the outermost region of the Solar System, approximately 148km (92miles) in diameter. It was first observed on 18 November 1998, by American astronomer Marc Buie and Robert Millis at the Kitt Peak National Observatory in Arizona, United States. In December 2000, a minor-planet moon, designated S/2000 1 with a diameter of 123km (76miles), was discovered in its orbit. After Charon in 1978, it was the first of nearly 100 satellites since discovered in the outer Solar System.
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.
As of 2018, this minor planet has not been numbered nor named by the Minor Planet Center.
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.
is a binary minor planet with a minor-planet moon in its orbit. 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 .
It was the first trans-Neptunian binary discovered after Charon in 1978, the largest satellite in the Pluto–Charon system. Since then nearly 100 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 eccentricity of with an exceptionally long orbital period of and a semi-major axis of .
While the primary measures, the satellite has a diameter of (a ratio of 0.883) with a combined system diameter of . The Collaborative Asteroid Lightcurve Link assumes an albedo of 0.10 and calculates a system diameter of based on an absolute magnitude of 6.7, while Mike Brown finds a diameter of with a lower albedo of 0.04.
As of 2020, no rotational lightcurve of has been obtained from photometric observations. The body's rotation period, pole and shape remain unknown.