2003 SS422

2003 SS₄₂₂ is a trans-Neptunian object located in the outermost region of the Solar System. It was discovered on 28 September 2003, by American astronomers at the Cerro Tololo Observatory in La Serena, Chile, and estimated to measure approximately 168 kilometers (104 miles) in diameter.^[1][3]

2003 SS₄₂₂

Discovery[1]
Discovered by	Cerro Tololo Obs.
Discovery site	Cerro Tololo Obs.
Discovery date	28 September 2003
Designations
MPC designation	2003 SS422
Minor planet category	TNO[2] · extreme[3] 1:16 Resonant distant[1]
Orbital characteristics[4]
Epoch 5 July 2021 (JD 2459400.5)
Uncertainty parameter 3[2]
Observation arc	14.92 yr (5,448 days)
Aphelion	356.788 AU
Perihelion	39.574 AU
Semi-major axis	198.181 AU
Eccentricity	0.8003140
Orbital period (sidereal)	2790 yr
Mean anomaly	1.770°
Mean motion	0° 0m 1.272s / day
Inclination	16.773°
Longitude of ascending node	150.949°
Argument of perihelion	206.824°
Physical characteristics
Mean diameter	163 km (est. at 0.09)[3]
Absolute magnitude (H)	7.04[4]

Due to the object's high eccentricity and large perihelia, 2003 SS₄₂₂ is an extreme trans-Neptunian object from the scattered disc (ESDO).^[3] It was a lost minor planet until it was recovered in June 2021.^[4]

Orbit and classification

Based on an observation arc of 14.9 years with 26 observations in total, 2003 SS₄₂₂ orbits the Sun at a distance of 39.6–356.8 AU once every 2790 years (1,019,048 days; semi-major axis of 198.2 AU). Its orbit has an eccentricity of 0.80 and an inclination of 17° with respect to the ecliptic.^[2]

As of 2021^[update], 2003 SS₄₂₂ belongs to a small number of 21 high-eccentricity and large-perihelia objects (q > 38 AU) with a semi-major axis of larger than 150 AU,^[5] which are the defining orbital parameters of the group of extreme scattered disc object, or ESDO. It is thought that objects cannot reach such orbits without some perturbing object outside the eight planets, which has led to the speculation of Planet Nine.

A study on dynamical classification of trans-Neptunian objects in 2024 identified 2003 SS₄₂₂ as most likely in a 1:16 resonance with Neptune, in which the object completes a single orbit for every 16 Neptune makes.^[6]