120347 Salacia
Salacia (minor-planet designation 120347 Salacia) is a large trans-Neptunian object in the Kuiper belt, approximately 850 km (530 mi) in diameter. It was discovered on 22 September 2004, by American astronomers Henry Roe, Michael Brown and Kristina Barkume at the Palomar Observatory in California, United States. Salacia orbits the Sun at an average distance that is slightly greater than that of Pluto. It was named after the Roman goddess Salacia and has a single known moon, Actaea.
Keck Telescope image of Salacia (bright, center) and its moon Actaea (faint, at left) | |
| Discovery | |
|---|---|
| Discovered by | H. G. Roe M. E. Brown K. M. Barkume |
| Discovery site | Palomar Obs. |
| Discovery date | 22 September 2004 |
| Designations | |
MPC designation | (120347) Salacia |
| Pronunciation | /səˈleɪʃə/ (sə-LAY-shə) |
Named after | Salacia (Roman mythology) |
Alternative designations | 2004 SB60 |
Minor planet category | TNO · Cubewano Extended |
| Adjectives | Salacian |
| Symbol | or |
| Orbital characteristics | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 3 | |
| Observation arc | 37.16 yr (13,572 days) |
| Earliest precovery date | 25 July 1982 |
| Aphelion | 46.670 AU |
| Perihelion | 37.697 AU |
Semi-major axis | 42.184 AU |
| Eccentricity | 0.10636 |
Orbital period (sidereal) | 273.98 yr (100,073 days) |
Mean anomaly | 123.138° |
Mean motion | 0° 0m 12.951s / day |
| Inclination | 23.921° |
Longitude of ascending node | 279.880° |
| 312.294° | |
| Known satellites | 1 (Actaea) |
| Physical characteristics | |
Mean diameter | 846±21 km 854±45 km (equal albedos) 866±37 km |
| Mass | (4.922±0.071)×1020 kg (system) (4.38±0.16)×1020 kg (system mass) |
Mean density | 1.5±0.12 g/cm3 1.29+0.29 −0.23 g/cm3 (system) 1.26±0.16 g/cm3 |
Synodic rotation period | 6.09 h (0.254 d) |
Sidereal rotation period | 6.09 h |
| 0.044±0.004 0.042±0.004 | |
| BB B−V=0.66±0.06 V−R=0.40±0.04 V−I=0.83±0.04 | |
| 20.7 | |
| 4.360±0.011 (system) 4.476±0.013 (Salacia) 6.850±0.053 (Actaea) 3.9 | |
Brown estimated that Salacia is nearly certainly a dwarf planet. However, William Grundy et al. argue that objects in the size range of 400–1,000 km, with densities of ≈ 1.2 g/cm3 or less and albedos less than ≈ 0.2, have likely never compressed into fully solid bodies or been resurfaced, let alone differentiated or collapsed into hydrostatic equilibrium, and so are highly unlikely to be dwarf planets. Salacia is at the upper end of this size range and has a very low albedo, though Grundy et al. later found it to have the relatively high density of 1.5±0.1 g/cm3.