|Discovered by||H. G. Roe
M. E. Brown
K. M. Barkume
|Discovery site||Palomar Obs.|
|Discovery date||22 September 2004|
|MPC designation||(120347) Salacia|
|Salacia (Roman mythology)|
|TNO  · Cubewano 
|Orbital characteristics |
|Epoch 16 February 2017 (JD 2457800.5)|
|Uncertainty parameter 3|
|Observation arc||34.05 yr (12,437 days)|
|270.98 yr (98,974 days)|
|0° 0m 12.96s / day|
|Known satellites||Actaea (±24 km) 286|
|Dimensions||±45 km (equal albedos) 854|
|Mass||±0.16)×1020 kg (system mass) (4.38|
−0.23 g/cm3 (system) 1.29
|6.09 h (0.254 d)|
Sidereal rotation period
±0.01 (Salacia) 0.87
±0.02 (Actaea) 0.89
|±0.011 (system) 4.360
±0.013 (Salacia) 4.476
±0.053 (Actaea) 6.850
120347 Salacia (sal-AY-shee-ə or sə-LAY-shə), provisional designation 2004 SB60, is a trans-Neptunian object in the Kuiper belt, approximately 850 kilometers in diameter and almost certainly a dwarf planet.
Salacia was discovered on 22 September 2004, by American astronomers Henry Roe, Michael Brown and Kristina Barkume at the Palomar Observatory in California, United States. It has been observed 100 times, with precovery images back to 1982. Salacia orbits the Sun at an average distance that is slightly larger than that of Pluto. It was named after the Roman goddess Salacia and has a single known moon, Actaea.
Salacia is a non-resonant object with a moderate eccentricity (0.107) and large inclination (23.9°), making it a scattered–extended object in the classification of the Deep Ecliptic Survey and a hot classical in the classification system of Gladman et al., which may be a non-distinction if they are part of a single population that formed during the outward migration of Neptune. Salacia's orbit is within the parameter space of the Haumea collisional family, but Salacia is not part of it, because it lacks the strong water-ice absorption bands typical of its members.
The total mass of the Salacia–Actaea system is ±0.16)×1020 kg, of which some 96% should be in Salacia itself, from the relative diameters. Salacia is large enough that it is unlikely to have a significant porosity and is likely differentiated. A rocky core (with a density 2.77–3.66 g/cm3) can be 0.4–0.65 of the total diameter of Salacia if its water-ice mantle is non-porous, and 0.45–0.7 of its total diameter if its mantle has 10% porosity. (4.38
Salacia has the lowest albedo and density known of any known big trans-Neptunian object. Salacia's infrared spectrum is almost featureless, indicating an abundance of water ice of less than 5% on the surface. Its light-curve amplitude is only 3%.
Salacia has one natural satellite, Actaea, that orbits its primary every 80±0.00016 d at a distance of 5.493±89 km and with an eccentricity of 5619±0.0076. It was discovered on 21 July 2006 by 0.0084Keith S. Noll, Harold Levison, Denise Stephens and Will Grundy with the Hubble Space Telescope.
Actaea is ±0.060 magnitudes fainter than Salacia, 2.372 implying a diameter ratio of 2.98 for equal albedos. Hence, assuming equal albedos, it has a diameter of ±24 km286 Actaea has the same color as Salacia (V−I = ±0.02 and 0.89±0.01, respectively), supporting the assumption of equal albedos. 0.87
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 have been tidally locked. 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. Salacia and Actaea will next occult each other in 2067.
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- Schaller, E. L.; Brown, M. E. (2008). "Detection of Additional Members of the 2003 EL61 Collisional Family via Near-Infrared Spectroscopy". Astrophysical Journal. Bibcode:2008ApJ...684L.107S. arXiv: . doi:10.1086/592232.
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- "IAUC 8751: (120347) 2004 SB_60; 2006gi, 2006gj; V733 Cep". Cbat.eps.harvard.edu. Retrieved 2014-06-14.
- "MPC/MPO/MPS Archive". Minor Planet Center. Retrieved 3 April 2017.