1998 WW31

Infobox Planet | discovery=yes | physical_characteristics=yes | bgcolour=#FFFFC0
name=mp|1998 WW|31
discoverer=Deep Ecliptic Survey
discovered=18 November, 1998
mp_name=mp|1998 WW|31
alt_names="none"
mp_category=Trans-Neptunian object
epoch=June 14, 2006 (JD 2453900.5)
semimajor=6655.451 Gm (44.489 AU)
perihelion=6067.553 Gm (40.559 AU)
aphelion=7243.350 Gm (48.419 AU)
eccentricity=0.088
period=108386.849 d (296.75 a)
inclination=6.818°
asc_node=237.108°
arg_peri=49.588°
mean_anomaly=126.983°
avg_speed=4.46 km/s
satellites=1
dimensions=133±15 km
mass=1.3–2.5e|18 kg (system)
density=1.5 g/cm³ (assumed)
surface_grav=0.025–0.031 m/s²
escape_velocity=0.054–0.068 km/s
sidereal_day=570 d (system orbital period)
spectral_type=?
abs_magnitude=6.05
albedo=0.05-0.09 (assumed)
single_temperature=~42 K mp|1998 WW|31 (also written 1998 WW31) is an object of the solar system located beyond the orbit of Neptune. It was discovered in 1998 by the Deep Ecliptic Survey (DES).

mp|1998 WW|31 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 the most symmetrical binary 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

* [http://cfa-www.harvard.edu/iauc/07600/07610.html The IAU circular announcing the discovery of the companion]
* [http://www.johnstonsarchive.net/astro/astmoons/am1998ww31.html mp|1998 WW|31 and S/2000 (1998 WW31) 1]
* [http://cfht.hawaii.edu/~veillet/WW31.html Discussion at CFHT, Hawaii]