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148780 Altjira
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 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 | |
| Pronunciation | /ælˈtʃɪərə/ |
Named after | Altjira |
| 2001 UQ18 | |
| 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) |
| 44.55 AU (6.665 Tm) | |
| Eccentricity | 0.0573 |
| 297.40 yr (108626±31 d) | |
| 129° | |
| 0.003314°/day | |
| Inclination | 5.198° |
| 1.84° | |
| 1919 Feb 16 ±37 days | |
| 304° | |
| Known satellites | 1 confirmed, 1 suspected |
| Physical characteristics | |
| Mass | (3.952±0.067)×1018 kg (system)[4] 2.338×1018 kg (primary)[a] |
Mean density | 0.30+0.50 −0.14 g/cm3[3] |
| 0.0430+0.1825 −0.0095[3] | |
| |
148780 Altjira (provisional designation 2001 UQ18) 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) of the primary vs. 221 kilometres (137 mi) to the secondary.[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]
In 2008, Altjira was named after the Arrernte creation deity, Altjira (Alchera).[1]
Physical characteristics
[edit]Altjira is a binary system consisting of two bodies of nearly equal size, making it a true synchronous binary rather than a typical primary-satellite system.[3]
Size and dimensions
[edit]Observations using thermal modeling indicate that the Altjira system has a combined effective diameter of approximately 331+51
−187 km.[3] The primary body has an estimated diameter of 246 (+38/−139) km, while the secondary body (the companion) possesses a radius of roughly 111 km (a diameter of ~222 km).[3]
Density and porosity
[edit]The bulk density of Altjira is exceptionally low, estimated at roughly 0.3+0.50
−0.14 g/cm3 (300 kg/m3).[3] This makes Altjira one of the least dense known large Kuiper belt objects (KBOs). Such an incredibly low density implies that the interiors of both bodies are highly porous, resembling loose "rubble piles" rather than solid ice or rock.
Albedo and color
[edit]Altjira has a relatively high geometric albedo, measured at 0.14±0.05.[3] It exhibits a very red surface color in the visible spectrum, which is a typical trait among cold classical Kuiper belt objects.
Satellite
[edit]| Discovery | |
|---|---|
| Discovery date | 6 August 2006[6] |
| Orbital characteristics[4] | |
| 9904±56 km | |
| Eccentricity | 0.3445±0.0045 |
| 139.561±0.047 d | |
| Inclination | 35.19°±0.19° (retrograde) |
| Satellite of | 148780 Altjira |
| Physical characteristics | |
| 221+34 −125 km[3] | |
| Mass | 1.695×1018 kg[b] |
| difference from primary: 0.7±0.2[6] | |
Altjira's companion was discovered on 6 August 2006, from images taken by the Hubble Space Telescope. The companion has no official designation.[1][c] 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.[8]
See also
[edit]- 47171 Lempo – the first and only confirmed hierarchical triple system in the Kuiper belt
- 58534 Logos – a contact binary and potential triple system in the cold classical Kuiper belt
Notes
[edit]- ^ Assuming a spherical diameter of 246 km and a density of 0.3 g/cm3
- ^ Assuming a spherical diameter of 221 km and a density identical to the primary
- ^ Nelsen et al. (2025) claim that Altjira's companion is designated "S/2007 (148780) 1", even though it was discovered in 2006.[8] The JPL Small Body Database and Johnston's Archive do not recognize any official designation for the companion.[1][9]
References
[edit]- ^ a b c d e f "JPL Small-Body Database Browser: 148780 Altjira (2001 UQ18)" (2022-11-28 last obs). Retrieved 2025-08-26.
- ^ Marc W. Buie. "Orbit Fit and Astrometric record for 148780". SwRI (Space Science Department). Retrieved 2011-11-29.
- ^ a b c d e f g h i j 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 c 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". 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 c d Johnston's Archive on (148780) Altjira Retrieved 2011-11-29
- ^ 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.
- ^ a b Nelsen, Maia A.; Ragozzine, Darin; Proudfoot, Benjamin C. N.; Giforos, William G.; Grundy, Will (March 2025). "Beyond Point Masses. IV. TNO Altjira is Likely a Hierarchical Triple Discovered Through Non-Keplerian Motion". The Planetary Science Journal. 6 (3): 53. arXiv:2403.12786. doi:10.3847/PSJ/ad864d.
- ^ Johnston, Wm. Robert (2014-09-20). "(148780) Altjira". Johnston's Archive. Retrieved 2026-08-05.
External links
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