Actaea (moon)
Salacia and its moon Actaea, imaged by the Keck telescope on 3 August 2010. Actaea is the fainter object to the left of Salacia. | |
| Discovery | |
|---|---|
| Discovered by | Keith S. Noll, Harold F. Levison, Denise C. Stephen, William M. Grundy |
| Discovery date | 21 July 2006 |
| Designations | |
Designation | Salacia I |
| Pronunciation | /ækˈtiːə/ |
| S/2006 (120347) 1 | |
| Adjectives | Actaean /ækˈtiːən/ |
| Orbital characteristics[1] | |
| 5700+30 −29 km[1] | |
| Eccentricity | 0.008+0.003 −0.003[1] |
| 5.49389±0.00001 days[1] | |
| Inclination | 17.2±0.5° |
| 108.9±1.6° | |
| 41+33 −22° | |
| Satellite of | Salacia |
| Physical characteristics | |
| 393±33 km[2] | |
| Mass | ≈ 20×1018 kg |
| 5.49389±0.00001 d (synchronous)[1] | |
| Albedo | 0.021±0.004[2] |
Spectral type | V–I = 0.89±0.02[3] |
| 6.850±0.053[3] | |
Actaea, formal designation (120347) Salacia I, is the only known moon of the classical Kuiper belt object 120347 Salacia. Its diameter is estimated to be 393 km (244 mi), which is approximately one-half the diameter of Salacia; thus, Salacia and Actaea are viewed by William Grundy et al. to be a binary system. Assuming that the following size estimates are correct, Actaea is about the fifth-biggest known moon of a trans-Neptunian object, after Charon (1212 km), Dysnomia (615 km),[4] Vanth (443 km),[5] and Ilmarë (403 km).[2]
Discovery and name
It was discovered on 21 July 2006 by Keith S. Noll, Harold Levison, Denise Stephens, and Will Grundy with the Hubble Space Telescope.[6] On 18 February 2011, it was officially named Actaea after the Nereid nymph Actaea.
Orbit
Actaea orbits its primary every 5.493 d at a distance of 5700+30
−29 km and with an eccentricity of 0.0084±0.0076.[1] The ratio of its semi-major axis to its primary's Hill radius is 0.0023, the tightest trans-Neptunian binary with a known orbit.[3]
Physical characteristics
The mass of the system is 4.861+0.076
−0.074×1020 kg,[1] with Actaea constituting perhaps 4% of this.[7]
Actaea is 2.372±0.060 magnitudes fainter than Salacia, implying a diameter ratio of 2.98 for equal albedos.[3] Hence, assuming equal albedos, it has a diameter of 393±33 km.[2] Actaea has the same color as Salacia (V−I = 0.89±0.02 and 0.87±0.01, respectively), supporting the assumption of equal albedos.[3] It has been calculated that the Salacia system should have undergone enough tidal evolution to circularize their orbits, which is consistent with the low measured eccentricity, but that the primary need not be tidally locked.[3] Salacia and Actaea will next occult each other in 2067.[3]
See also
- Ilmarë, a similarly sized moon orbiting 174567 Varda
- Hiʻiaka, a similarly sized moon orbiting the dwarf planet Haumea
References
- ^ a b c d e f g Collyer, Cameron; Fernandez-Valenzuela, Estela; Jose Luis Ortiz; Holler, Bryan J.; Proudfoot, Benjamin; Morales, Nicolas; Morales, Rafael; Benecchi, Susan; Rommel, Flavia L.; Grundy, Will; Ragozzine, Darin (2025). "Synchronous Rotation in the (120347) Salacia-Actaea System". arXiv:2509.02734 [astro-ph.EP].
- ^ a b c d Kiss, Csaba; Gabányi, Krisztina; Moór, Attila; Müller, Thomas; Fernandez-Valenzuela, Estela; Moullet, Arielle; Borkovits, Tamás; Kalup, Csilla (2025-07-09). ALMA submm measurements of the trans-Neptunian binary system satellites Ilmarë, Actaea, Hi'iaka and Namaka (Report). Copernicus Meetings.
- ^ a b c d e f g Stansberry, J.A.; Grundy, W.M.; Mueller, M.; et al. (2012). "Physical Properties of Trans-Neptunian Binaries (120347) Salacia–Actaea and (42355) Typhon–Echidna". Icarus. 219 (2): 676–688. Bibcode:2012Icar..219..676S. CiteSeerX 10.1.1.398.6675. doi:10.1016/j.icarus.2012.03.029.
- ^ Brown, Michael E.; Butler, Bryan J. (2023-10-01). "Masses and Densities of Dwarf Planet Satellites Measured with ALMA". The Planetary Science Journal. 4 (10): 193. arXiv:2307.04848. Bibcode:2023PSJ.....4..193B. doi:10.3847/PSJ/ace52a.
- ^ Sickafoose, A. A.; Bosh, A. S.; Levine, S. E.; Zuluaga, C. A.; Genade, A.; Schindler, K.; Lister, T. A.; Person, M. J. (2019-02-01). "A stellar occultation by Vanth, a satellite of (90482) Orcus". Icarus. 319: 657–668. arXiv:1810.08977. Bibcode:2019Icar..319..657S. doi:10.1016/j.icarus.2018.10.016. S2CID 119099266.
- ^ "IAUC 8751: (120347) 2004 SB_60; 2006gi, 2006gj; V733 Cep". Cbat.eps.harvard.edu. Archived from the original on 2013-12-03. Retrieved 2014-06-14.
- ^ Grundy, W. M.; Noll, K. S.; Roe, H. G.; Buie, M. W.; Porter, S. B.; Parker, A. H.; et al. (2019). "Mutual Orbit Orientations of Transneptunian Binaries" (PDF). Icarus. 334: 62–78. Bibcode:2019Icar..334...62G. doi:10.1016/j.icarus.2019.03.035. ISSN 0019-1035. S2CID 133585837. Retrieved 2019-10-26.