(119979) 2002 WC19

(119979) 2002 WC₁₉ (provisional designation 2002 WC₁₉) is a twotino, that is, a planetoid in a 1:2 orbital resonance with Neptune. It was discovered on November 16, 2002 at the Palomar Observatory. If its derived diameter is correct it would have a higher density than Pluto, which is unusual as it appears to be much smaller than the expected size at which a Kuiper belt object usually becomes solid.

(119979) 2002 WC₁₉

2002 WC19 and its satellite imaged by the Hubble Space Telescope in 2007
Discovery
Discovered by	Palomar Observatory
Discovery date	16 November 2002
Designations
MPC designation	(119979) 2002 WC19
Minor planet category	Twotino[1][2] binary
Orbital characteristics[3]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 3
Observation arc	3978 days (10.89 yr)
Aphelion	60.732 AU (9.0854 Tm)
Perihelion	35.289 AU (5.2792 Tm)
Semi-major axis	48.010 AU (7.1822 Tm)
Eccentricity	0.26498
Orbital period (sidereal)	332.67 yr (121,507 d)
Mean anomaly	316.02°
Mean motion	0° 0m 10.666s / day
Inclination	9.1746°
Longitude of ascending node	109.7547°
Time of perihelion	≈ 5 November 2056[4] ±3 days
Argument of perihelion	44.356°
Known satellites	1 (81 km)[5]
Earth MOID	34.3056 AU (5.13204 Tm)
Jupiter MOID	29.9229 AU (4.47640 Tm)
Physical characteristics
Dimensions	338 km[5]
Mass	(8.13±1.0)×1019 kg (prograde) or (7.263±0.87)×1019 kg (retrograde) [6]
Mean density	1.97 g/cm3[5]
Geometric albedo	0.05[5]
Absolute magnitude (H)	4.9

Knowing how many twotinos there are may reveal whether Neptune took roughly 1 million or 10 million years to migrate about 7 AU from its birth location.^[7]

Satellite

On February 27, 2007, a natural satellite was reported to be orbiting (119979) 2002 WC₁₉. It is estimated to be 4092±94 km from the primary, with an orbital period of 8.403±0.001 days, an eccentricity of 0.21±0.05 and an inclination of 24.0°±0.7°. Assuming similar albedos, it is a quarter the diameter of its primary, or around 81 kilometres (50 mi) in diameter.^[5]

• 
  Orbit of 2002 WC₁₉ compared to Pluto and Neptune
• 
  1:2 libration over 20,000 years – Neptune is held stationary (dot at 5 o'clock); orbit of Uranus in blue