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(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; August 2006 (secondary)
Designations
MPC designation	(148780) Altjira
Pronunciation	/ælˈtʃɪrə/
Alternative designations	2001 UQ18
Minor planet category	Cubewano (DES)
Adjectives	Altjirian
Orbital characteristics
	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)
Mass	3.952×1018 kg
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)	5.7 5.6, 5.4, or 5.1 (primary); secondary's magnitude difference with primary's: 0.7 ± 0.2

148780 Altjira /ælˈtʃɪrə/ is a binary classical Kuiper belt object (cubewano).^[2] The secondary, S/2007 (148780) 1, 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]

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]

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]

References

^ ^a ^b ^c ^d "JPL Small-Body Database Browser: 148780 Altjira (2001 UQ18)" (2008-10-02 last obs). Retrieved 26 March 2016.
^ ^a ^b ^c ^d ^e Johnston's Archive on (148780) Altjira Retrieved 2011-11-29
^ Marc W. Buie. "Orbit Fit and Astrometric record for 148780". SwRI (Space Science Department). Retrieved 2011-11-29.
^ ^a ^b ^c ^d Vilenius, E.; Kiss, C.; Mommert, M.; et al. (2014). ""TNOs are Cool": A survey of the trans-Neptunian region X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations". Astronomy & Astrophysics. 564: A35. arXiv:1403.6309. Bibcode:2014A&A...564A..35V. doi:10.1051/0004-6361/201322416. S2CID 118513049.
^ ^a ^b Grundy, W. M.; Noll, K. S.; Nimmo, F.; Roe, H. G.; Buie, M. W.; Porter, S. B.; Benecchi, S. D.; Stephens, D. C.; Levison, H. F.; Stansberry, J. A. (2011). "Five new and three improved mutual orbits of transneptunian binaries" (PDF). Icarus. 213 (2): 678. arXiv:1103.2751. Bibcode:2011Icar..213..678G. doi:10.1016/j.icarus.2011.03.012. S2CID 9571163.
^ Doressoundiram, A.; Peixinho, N.; Doucet, C.; Mousis, O.; Barucci, M. A.; Petit, J. M.; Veillet, C. (2005). "The Meudon Multicolor Survey (2MS) of Centaurs and trans-neptunian objects: extended dataset and status on the correlations reported". Icarus. 174 (1): 90–104. Bibcode:2005Icar..174...90D. doi:10.1016/j.icarus.2004.09.009. S2CID 122936619.
^ ^a ^b Duffard, R.; Ortiz, J. L.; Thirouin, A.; Santos-Sanz, P.; Morales, N. (2009). "Transneptunian objects and Centaurs from light curves". Astronomy & Astrophysics. 505 (3): 1283–1295. arXiv:0910.1472. Bibcode:2009A&A...505.1283D. doi:10.1051/0004-6361/200912601.
^ Nelsen, Maia A.; Ragozzine, Darin; Proudfoot, Benjamin C. N.; Giforos, William G.; Grundy, Will (2024-03-19). "Beyond Point Masses. IV. TNO Altjira is Likely a Hierarchical Triple Discovered Through Non-Keplerian Motion". arXiv:2403.12786 [astro-ph.EP].