120347 Salacia

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120347 Salacia
Discovered by Henry G. Roe, Michael E. Brown, Kristina M. Barkume
Discovery date 22 September 2004
MPC designation (120347) 2004 SB60
Pronunciation /sæˈlʃiə/ (sal-AY-shee-ə) or
/səˈlʃə/ (sə-LAY-shə)
Cubewano (MPC)[1]
Extended (DES)[2]
Orbital characteristics[3]
Epoch 13 January 2016 (JD 2457400.5)
Uncertainty parameter 3
Observation arc 10330 days (28.28 yr)
Aphelion 46.425 AU (6.9451 Tm)
Perihelion 37.296 AU (5.5794 Tm)
41.860 AU (6.2622 Tm)
Eccentricity 0.10905
270.84 yr (98924 d)
Inclination 23.936°
Known satellites Actaea (286±24 km)
Earth MOID 36.338 AU (5.4361 Tm)
Jupiter MOID 32.2291 AU (4.82140 Tm)
Physical characteristics
Dimensions 854±45 km (equal albedos)[4]
Mass (4.38±0.16)×1020 kg (system mass)[4][5]
Mean density
6.09 h (0.254 d)
6.09 h[3]
V−I =
0.87±0.01 (Salacia)
0.89±0.02 (Actaea)[5]
4.360±0.011 (system)[5]
4.476±0.013 (Salacia)[5]
6.850±0.053 (Actaea)[5]

120347 Salacia[6] is a large planetoid in the Kuiper belt. It was discovered on 22 September 2004 by Henry G. Roe, Michael E. Brown and Kristina M. Barkume at the Palomar Observatory. It is almost certainly a dwarf planet.[7] Salacia's diameter is estimated to be about 850 kilometres (530 mi) due to a low albedo. It has been observed 100 times, with precovery images back to 1982.[3] Salacia orbits the Sun at an average distance that is slightly larger than that of Pluto. It has a single known moon, Actaea.



Salacia was discovered on 22 September 2004 by Henry G. Roe, Michael E. Brown, and Kristina M. Barkume at the Palomar Observatory and assigned the provisional designation (120347) 2004 SB60.


It was named Salacia /sæˈlʃə/ on 18 February 2011, after Salacia, the goddess of salt water and the wife of Neptune.[8]

The moon's name, Actaea /ækˈtə/, was assigned on the same date. Actaea is a nereid or sea nymph.


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.,[9] which may be a non-distinction if they are part of a single population that formed during the outward migration of Neptune.[5] 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.[5]

Physical characteristics[edit]

The total mass of the Salacia–Actaea system is (4.38±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.

Salacia has the lowest albedo and density known of any known big trans-Neptunian object.[5] Salacia's infrared spectrum is almost featureless, indicating an abundance of water ice of less than 5% on the surface.[4][10] Its light-curve amplitude is only 3%.[5]

Mike Brown's website lists Salacia as nearly certainly a dwarf planet,[7] but the IAU has not formally recognized it as such.[11][12]


Salacia has one natural satellite, Actaea, that orbits its primary every 5.49380±0.00016 d at a distance of 5619±89 km and with an eccentricity of 0.0084±0.0076. It was discovered on 21 July 2006 by Keith S. Noll, Harold Levison, Denise Stephens and Will Grundy with the Hubble Space Telescope.[13]

Actaea is 2.372±0.060 magnitudes fainter than Salacia,[4] implying a diameter ratio of 2.98 for equal albedos.[5] Hence, assuming equal albedos, it has a diameter of 286±24 km[4] 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.[5]

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.[5] 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.[5] Salacia and Actaea will next occult each other in 2067.[5]


  1. ^ "MPEC 2009-R09 :Distant Minor Planets (2009 SEPT. 16.0 TT)". IAU Minor Planet Center. 2009-09-04. Retrieved 2011-07-05. 
  2. ^ Buie, Marc W. "Orbit Fit and Astrometric record for 120347" (2007-08-12 using 62 of 73 observations). SwRI (Space Science Department). Retrieved 2009-10-04. 
  3. ^ a b c d "JPL Small-Body Database Browser: 120347 Salacia (2004 SB60)" (2010-11-05 last obs). Retrieved 26 March 2016. 
  4. ^ a b c d e f g Fornasier, S.; Lellouch, E.; Müller, P., T.; et al. (2013). "TNOs are Cool: A survey of the trans-Neptunian region. VIII. Combined Herschel PACS and SPIRE observations of 9 bright targets at 70–500 µm". Astronomy & Astrophysics. 555: A92. arXiv:1305.0449v2Freely accessible. Bibcode:2013A&A...555A..15F. doi:10.1051/0004-6361/201321329. 
  5. ^ a b c d e f g h i j k l m n 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: 676–688. Bibcode:2012Icar..219..676S. CiteSeerX accessible. doi:10.1016/j.icarus.2012.03.029. 
  6. ^ MPC 73984
  7. ^ a b Brown, Michael E. "How many dwarf planets are there in the outer solar system? (updates daily)". California Institute of Technology. Retrieved 2016-11-29. 
  8. ^ Johnston's Archive
  9. ^ Gladman, B.; Marsden, B. G.; VanLaerhoven, C. (2008). "Nomenclature in the Outer Solar System". The Solar System Beyond Neptune (PDF). p. 43. 
  10. ^ Schaller, E. L.; Brown, M. E. (2008). "Detection of Additional Members of the 2003 EL61 Collisional Family via Near-Infrared Spectroscopy". Astrophysical Journal. arXiv:0808.0185Freely accessible. Bibcode:2008ApJ...684L.107S. doi:10.1086/592232. 
  11. ^ "Planetary Names: Planet and Satellite Names and Discoverers". Gazetteer of Planetary Nomenclature. International Astronomical Union (Working Group for Planetary System Nomenclature). Retrieved 10 June 2012. 
  12. ^ "List of Dwarf Planets". NASA. Retrieved 2012-06-09. 
  13. ^ "IAUC 8751: (120347) 2004 SB_60; 2006gi, 2006gj; V733 Cep". Cbat.eps.harvard.edu. Retrieved 2014-06-14. 

External links[edit]