148780 Altjira

Satellite
Discovery
Discovery date	6 August 2006
Orbital characteristics
Semi-major axis	9904±56 km
Eccentricity	0.3445±0.0045
Orbital period (sidereal)	139.561±0.047 d
Inclination	35.19°±0.19° (retrograde)
Satellite of	148780 Altjira
Physical characteristics
Mean diameter	221+34; −125 km
Absolute magnitude (H)	difference from primary: 0.7±0.2

(148780) Altjira
	Altjira and its companion imaged by the Hubble Space Telescope in 2006
Discovery
Discovery site	Deep Ecliptic Survey at Kitt Peak
Discovery date	20 October 2001
Designations
MPC designation	(148780) Altjira
Pronunciation	/ælˈtʃɪərə/
Named after	Altjira
Alternative designations	2001 UQ18
Minor planet category	Classical KBO (DES)
Orbital characteristics
	Epoch 2025 May 05 (JD 2460800.5)
	Uncertainty parameter 4
Observation arc	7,709 days (21.11 yr)
Aphelion	47.11 AU (7.048 Tm)
Perihelion	42.00 AU (6.283 Tm)
Semi-major axis	44.55 AU (6.665 Tm)
Eccentricity	0.0573
Orbital period (sidereal)	297.40 yr (108626±31 d)
Mean anomaly	129°
Mean motion	0.003314°/day
Inclination	5.198°
Longitude of ascending node	1.84°
Time of perihelion	1919 Feb 16 ±37 days
Argument of perihelion	304°
Known satellites	1 confirmed, 1 suspected
Physical characteristics
Mean diameter	331+51; −187 km (combined); 246+38; −139 km (primary);
Mass	(3.952±0.067)×1018 kg (system)
Mean density	0.30+0.50; −0.14 g/cm3
Geometric albedo	0.0430+0.1825; −0.0095
Spectral type	B−V = 0.91±0.13; V−R = 0.74±0.08; V−I = 1.17±0.09;
Absolute magnitude (H)	5.77;; 5.4 (system), 5.1 (primary) ;

148780 Altjira (provisional designation 2001 UQ₁₈) appears to be a triple or contact binary double classical Kuiper belt object. The secondary is large compared to the primary, approximately 246 kilometres (153 mi) vs. 221 kilometres (137 mi). The lightcurve is quite flat (Δmag < 0.10), which is indicative of a "quasi-spherical body with a homogeneous surface". The system mass is 4×10¹⁸ kg.

Its companion was discovered on 6 August 2006, from images taken by the Hubble Space Telescope. The secondary's orbit has the following parameters: semi-major-axis, 9904±56 km; period, 139.561±0.047 d; eccentricity, 0.3445±0.0045; and inclination, 35.19°±0.19° (retrograde). There is indirect evidence that Altjira may be an unresolved hierarchical triple system.

In 2008, Altjira was named after the Arrernte creation deity, Altjira (Alchera).