(148975) 2001 XA255

(148975) 2001 XA₂₅₅
Discovery
Discovered by	David C. Jewitt, Scott S. Sheppard and Jan Kleyna
Discovery date	9 December 2001
Designations
MPC designation	(148975) 2001 XA255
Minor planet category	Centaur
Orbital characteristics
	Epoch 13 January 2016 (JD 2457400.5)
	Uncertainty parameter 2
Observation arc	3812 days (10.44 yr)
Aphelion	48.731 AU (7.2901 Tm)
Perihelion	9.3364 AU (1.39671 Tm)
Semi-major axis	29.034 AU (4.3434 Tm)
Eccentricity	0.67843
Orbital period (sidereal)	156.44 yr (57141.1 d)
Mean anomaly	12.809°
Mean motion	0° 0m 22.681s / day
Inclination	12.628°
Longitude of ascending node	105.89°
Argument of perihelion	90.452°
Jupiter MOID	4.12722 AU (617.423 Gm)
Physical characteristics
Mean diameter	12.5 km; 38 km
Geometric albedo	0.041
Absolute magnitude (H)	11.1

(148975) 2001 XA₂₅₅, provisional designation: 2001 XA₂₅₅, is a dark minor planet in the outer Solar System, classified as centaur, approximately 38 kilometers (24 miles) in diameter.^[1] It was discovered on 9 December 2001, by David C. Jewitt, Scott S. Sheppard, and Jan Kleyna observing from the Mauna Kea Observatory.^[4] The object is currently trapped in a 1:1 mean-motion resonance with Neptune following a path of the horseshoe type.^[5]

Orbit and classification

2001 XA₂₅₅ follows a very eccentric orbit (0.68) with perihelion just inside the orbit of Saturn, aphelion in the trans-Neptunian belt and a semi-major axis of 28.9 AU. The orbital inclination of this object is moderate at 12.6º.^[1]

Resonance with Neptune

2001 XA₂₅₅ was identified as trapped in a 1:1 mean-motion resonance with Neptune and 1:2 with Uranus by T. Gallardo in 2006.^[6] The object is dynamically unstable and it entered the region of the giant planets relatively recently, perhaps 50,000 years ago, from the scattered disk. It follows a short-lived horseshoe orbit around Neptune.^[5]

Physical characteristics

The object has an estimated diameter of 12.5 km and it was classified as an inactive centaur by David Jewitt.^[2] Observations by the NEOWISE mission gave a larger diameter of 37.7 kilometers and an albedo of 0.041.^[3] It has an absolute magnitude is 11.1.^[1]