148780 Altjira

148780 Altjira /ælˈtʃɪrə/ is a triple or contact-binary double classical Kuiper belt object (cubewano).^[2] The secondary is large compared to the primary, approximately 246 kilometres (153 mi) vs. 221 kilometres (137 mi).^[4] The Altjiran lightcurve is quite flat (Δmag<0.10), which is indicative of a "quasi-spherical body with a homogeneous surface".^[7]

(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 August 2006 (secondary)[2]
Designations
MPC designation	(148780) Altjira
Pronunciation	/ælˈtʃɪrə/
Alternative designations	2001 UQ18
Minor planet category	Cubewano (DES)[3]
Adjectives	Altjirian
Orbital characteristics[1]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 3
Observation arc	2539 days (6.95 yr)
Aphelion	46.877 AU (7.0127 Tm)
Perihelion	41.572 AU (6.2191 Tm)
Semi-major axis	44.224 AU (6.6158 Tm)
Eccentricity	0.059979
Orbital period (sidereal)	294.10 yr (107421 d)
Mean anomaly	124.29°
Mean motion	0.0033513°/day
Inclination	5.2056°
Longitude of ascending node	2.0132°
Argument of perihelion	297.71°
Known satellites	1
Physical characteristics
Mean diameter	331+51 −187 km (combined) 246+38 −139 km (primary) 221+34 −125 km (secondary)[4]
Mass	3.952×1018 kg[5]
Mean density	0.30+0.50 −0.14 g/cm3[4]
Geometric albedo	0.0430+0.1825 −0.0095[4]
Spectral type	B−V = 0.91±0.13 V−R = 0.74±0.08 V−I = 1.17±0.09[6]
Absolute magnitude (H)	5.7[1] 5.6,[7] 5.4,[2] or 5.1[2] (primary) secondary's magnitude difference with primary's: 0.7 ± 0.2[2]

The satellite'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). The total system mass is about 4 × 10¹⁸ kg.^[5]

Artistic concept of the Altjira system

It was named after the Arrernte creation deity, Altjira, who created the Earth during the Dreamtime and then retired to the sky.^[1]

Altjira may be an unresolved hierarchical triple system.^[8]