 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 anatural satellite of theclassical Kuiper belt object120347 Salacia. Itsdiameter is estimated to be 393 km (244 mi), which is approximately one-half thediameter ofSalacia; thus,Salacia and Actaea are viewed by William Grundy et al. to be abinary system. Assuming that the followingsize estimates are correct, Actaea is about the fifth-biggest knownmoon of atrans-Neptunian object, afterCharon (1212 km),Dysnomia (615 km),[4]Vanth (443 km),[5] andIlmarë (403 km).[2]
It was discovered on 21 July 2006 byKeith S. Noll,Harold Levison,Denise Stephens, and Will Grundy with theHubble Space Telescope.[6] On 18 February 2011, it was officially named Actaea after theNereid nymphActaea.
Actaea orbits its primary every5.493 d at a distance of5700+30
−29 km and with aneccentricity of0.0084±0.0076.[1] The ratio of itssemi-major axis to its primary'sHill radius is 0.0023, the tightest trans-Neptunianbinary with a knownorbit.[3]
Themass of the system is4.861+0.076
−0.074×1020 kg,[1] with Actaea constituting perhaps 4% of this.[7] Actaea is2.372±0.060 magnitudes fainter than Salacia, implying a diameter ratio of 2.98 for equalalbedos.[3] Hence, assuming equal albedos, it has a diameter of393±33 km.[2] Actaea has the same color as Salacia (V−I =0.89±0.02 and0.87±0.01, respectively), supporting the assumption of equalalbedos.[3] It has been calculated that the Salacia system should have undergone enoughtidal evolution to circularize theirorbits, which is consistent with the low measuredeccentricity, but that the primary need not betidally locked.[3] Salacia and Actaea will next occult each other in 2067.[3]