148780 Altjira

148780 Altjira appears to be a triple or contact-binary double classical Kuiper belt object.^[6] The secondary is large compared to the primary, approximately 246 kilometres (153 mi) vs. 221 kilometres (137 mi).^[3] The lightcurve is quite flat (Δmag<0.10), which is indicative of a "quasi-spherical body with a homogeneous surface".^[7] The system mass is 4 × 10¹⁸ kg.^[4]

(148780) Altjira

Altjira and its companion imaged by the Hubble Space Telescope in 2006
Discovery
Discovery site	Deep Ecliptic Survey at Kitt Peak[1]
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)[2]
Orbital characteristics[1]
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)[3]
Mass	(3.952±0.067)×1018 kg (system)[4]
Mean density	0.30+0.50 −0.14 g/cm3[3]
Geometric albedo	0.0430+0.1825 −0.0095[3]
Spectral type	B−V = 0.91±0.13 V−R = 0.74±0.08 V−I = 1.17±0.09[5]
Absolute magnitude (H)	5.77;[1] 5.4 (system), 5.1 (primary) [6]

Satellite

Discovery
Discovery date	6 August 2006[6]
Orbital characteristics[4]
Semi-major axis	9904±56 km
Eccentricity	0.3445±0.0045
Orbital period (sidereal)	0.047139.561 d
Inclination	35.19 (retrograde)
Satellite of	148780 Altjira
Physical characteristics
Mean diameter	221+34 −125 km[3]
Absolute magnitude (H)	difference from primary: 0.7 ± 0.2[6]

Its companion was discovered on 6 August 2006, from images taken by the Hubble Space Telescope.^[8] The secondary's orbit has the following parameters: semi-major-axis, 9904 ± 56 km; period, 139.561 ± 0.047 days; 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.^[9]

In 2008, Altjira was named after the Arrernte creation deity, Altjira (Alchera).^[1]