 Keck Telescope image of Salacia (bright, center) and its moonActaea (faint, at left) | |
| Discovery[1][2] | |
|---|---|
| Discovered by | H. G. Roe M. E. Brown K. M. Barkume |
| Discovery site | Palomar Obs. |
| Discovery date | 22 September 2004 |
| Designations | |
| (120347) Salacia | |
| Pronunciation | /səˈleɪʃə/ (sə-LAY-shə) |
Named after | Salacia(Roman mythology)[2] |
| 2004 SB60 | |
| TNO[1] · classical (hot)[3] extended[4] | |
| Adjectives | Salacian |
| Symbol | .svg) or.svg) (rare) |
| Orbital characteristics[1] | |
| Epoch 31 May 2020 (JD 2459000.5) | |
| Uncertainty parameter 3 | |
| Observation arc | 37.16 yr (13,572 days) |
| Earliestprecovery date | 25 July 1982 |
| Aphelion | 46.670AU |
| Perihelion | 37.697 AU |
| 42.184 AU | |
| Eccentricity | 0.10636 |
| 273.98yr (100,073 days) | |
| 123.138° | |
| 0° 0m 12.951s / day | |
| Inclination | 23.921° |
| 279.880° | |
| 312.294° | |
| Knownsatellites | 1 (Actaea) |
| Physical characteristics | |
| Mass | 4.861+0.076 −0.074×1020 kg (System mass)[8] |
Meandensity | 1.50±0.12 g/cm3[6] 1.26±0.16 g/cm3[7] |
| 5.49403±0.00016 d (synchronous)[8] | |
| 0.041±0.004 (2025)[5] 0.042±0.004 (2017)[7] | |
| BB[9] B−V=0.66±0.06[9] V−R=0.40±0.04[9] V−I=0.83±0.04[9] | |
| 20.7 | |
| 4.360±0.011 (Salacia+Actaea)[3] 4.476±0.013 (Salacia)[3] 6.850±0.053 (Actaea)[3] 4.15[1] | |
Salacia (minor-planet designation:120347 Salacia) is a largetrans-Neptunian object (TNO) andpossible dwarf planet in theKuiper belt that is probably between 800 km (500 mi) and 875 km (544 mi) in diameter. It was discovered on 22 September 2004, by American astronomersHenry Roe,Michael Brown and Kristina Barkume at thePalomar Observatory in California, United States. Salacia orbits the Sun at an average distance that is slightly greater than that ofPluto. It was named after the Roman goddessSalacia and has a single known moon,Actaea. Salacia and Actaea form abinary system where both bodies aretidally locked to each other, similar to Pluto andCharon.[8]
Salacia is a non-resonant object with a moderate eccentricity (0.11) and large inclination (23.9°), making it ascattered–extended object in the classification of theDeep Ecliptic Survey and ahot classical Kuiper belt object in the classification system of Gladmanet al.,[10] which may be the same thing if they are part of a single population that formed during theoutward migration of Neptune.[3] Salacia's orbit is within theparameter space of theHaumea collisional family, but Salacia is not part of it, as evidenced by its lack of the strong water-ice absorption bands.[3]
As of 2019, the total mass of the Salacia–Actaea system is estimated at4.861+0.076
−0.074×1020 kg,[8] with an average systemdensity of1.5±0.1 g/cm3; Salacia itself is estimated to be around 838 km in diameter.[5] Salacia has the lowestalbedo of any known largetrans-Neptunian object.[3] According to the estimate from 2017 based on an improved thermophysical modelling, thesize of Salacia is slightly larger at 866 km and itsdensity therefore slightly lower (calculated at1.26 g/cm3 with the oldmass estimate discussed below).[7]
William Grundyet al. describe Salacia as a 'dwarf planet–sized TNO'.[6] They had earlier rejected it as adwarf planet due to its low estimated density,[11] but backed off that position when they later found it to have the relatively highdensity of1.5 g/cm3, though Salacia's extremely lowalbedo of 4% remains consistent with a lack of the kind of geological activity that is thought to be typical ofdwarf planets.[6]
Salacia'sinfrared spectrum is almost featureless, indicating an abundance ofwater ice of less than 5% on the surface.[12][13]Near-infraredspectroscopy by theJames Webb Space Telescope (JWST) in 2022 revealed the presence ofwater ice in Salacia's surface.[14] No signs ofvolatile ices such asmethane were detected in JWST's spectrum of Salacia.[14] Itslight-curve amplitude is only 3%.[3]
Salacia has one knownnatural satellite,Actaea, that orbits its primary every5.49380±0.00016 d at adistance of5700+30
−29 km[8] and with aneccentricity of0.0084±0.0076. It was discovered on 21 July 2006 byKeith Noll,Harold Levison,Denise Stephens and William Grundy with theHubble Space Telescope.[15]
Actaea is probably between 360 km (220 mi) and 425 km (264 mi) indiameter.[5] It is2.372±0.060 magnitudes fainter than Salacia,[12] implying a diameter ratio of 3 for equalalbedos.[3] Actaea has the same color as Salacia (V−I =0.89±0.02 and0.87±0.01, respectively), supporting the assumption of equal albedos.[3]
It has been calculated that the Salacia system should have undergone enoughtidal evolution to circularize theirorbits, which is consistent with the low measuredeccentricity.[3] The ratio of itssemi-major axis to its primary'sHill radius is 0.0023, the tightest trans-Neptunianbinary with a known orbit.[3] Salacia and Actaea will next occult each other in 2067.[3]
This minor planet was named afterSalacia (/səˈleɪʃə/), the goddess of salt water and the wife ofNeptune.[2] The naming citation was published on 18 February 2011 (M.P.C. 73984).[16]
The moon's name,Actaea/ækˈtiːə/, was assigned on the same date. Actaea is anereid or sea nymph.
Planetary symbols are no longer used much in astronomy, so Salacia never received a symbol in the astronomical literature. Denis Moskowitz, a software engineer who designed most of the dwarf planet symbols, proposed a stylisedhippocamp (.svg)
, formerly.svg)
) as the symbol for Salacia;[17][18] this symbol is not widely used.
| Consensus | _(cropped).jpg)  | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Candidate (for TNOs, D+1σ ≥ 700 km or H ≤ 4.0) |
| ||||||||||||
| Planetary satellites of |    | |
|---|---|---|
| Dwarf planet satellites of | ||
| Minor-planet moons | ||
| Ranked by size | ||
