astro.wikisort.org - Asteroid

120347 Salacia, provisional designation 2004 SB₆₀, is a large planetoid in the Kuiper belt, approximately 850 kilometers in diameter. As of 2018, it is located 44.8 astronomical units from the Sun, and reaches apparent magnitude 20.7 at opposition.

120347 Salacia

Salacia and its moon Actaea, imaged by the Hubble Space Telescope on 21 July 2006.
Discovery[1][2]
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)[2]
Alternative designations	2004 SB60
Minor planet category	TNO[1] · Cubewano[3] Extended[4]
Adjectives	Salacian
Orbital characteristics[1]
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°
Argument of perihelion	312.294°
Known satellites	1 (Actaea)
Physical characteristics
Mean diameter	846±21 km[5][lower-alpha 1] 854±45 km (equal albedos)[6] 866±37 km[7]
Mass	(4.922±0.071)×1020 kg (system)[5] (4.38±0.16)×1020 kg (system mass)[6][8]
Mean density	1.5±0.12 g/cm3[5] 1.29+0.29 −0.23 g/cm3 (system)[6] 1.26±0.16 g/cm3[7]
Synodic rotation period	6.09 h (0.254 d)
Sidereal rotation period	6.09 h[1]
Geometric albedo	0.044±0.004[6] 0.042±0.004[7]
Spectral type	BB[9] B−V=0.66±0.06[9] V−R=0.40±0.04[9] V−I=0.83±0.04[9]
Apparent magnitude	20.7
Absolute magnitude (H)	4.360±0.011 (system)[8] 4.476±0.013 (Salacia)[8] 6.850±0.053 (Actaea)[8] 3.9[1]

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 124 times, with precovery images back to 25 July 1982.[2] 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.

Brown estimated that Salacia is nearly certainly a dwarf planet.[10] However, William Grundy et al. argue that objects in the size range of 400–1000 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.[11] 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.[5]

Orbit

Salacia is a non-resonant object with a moderate eccentricity (0.11) 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.,[12] which may be a non-distinction if they are part of a single population that formed during the outward migration of Neptune.[8] 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.[8]

Physical characteristics

As of 2019, the total mass of the Salacia–Actaea system is estimated at (4.922±0.071)×10²⁰ kg, with an average system density of 1.51 g/cm³; Salacia itself is estimated to be around 846 km in diameter.[5] Salacia has the lowest albedo of any known large trans-Neptunian object.[8] According to the estimate from 2017 based on an improved thermophysical modelling the size of Salacia is slightly different at 866 km and its density is therefore lower being 1.26 g/cm³ (based on old mass).[7]

Salacia was previously believed to have a mass of around (4.38±0.16)×10²⁰ kg, in which case it would also have had the lowest density (around 1.29 g/cm³) of any known large TNO;[6] William Grundy and colleagues proposed that this low density would imply that Salacia never collapsed into a solid body, in which case it would not be in hydrostatic equilibrium.[11] Salacia's infrared spectrum is almost featureless, indicating an abundance of water ice of less than 5% on the surface.[6][13] Its light-curve amplitude is only 3%.[8]

Satellite

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 Noll, Harold Levison, Denise Stephens and William Grundy with the Hubble Space Telescope.[14]

Actaea is 2.372±0.060 magnitudes fainter than Salacia,[6] implying a diameter ratio of 2.98 for equal albedos.[8] Hence, assuming equal albedos, it has a diameter of 286±24 km[6] According to the estimate from 2017 based on an improved modelling the size of Actaea is slightly larger being 290±21 km.[7]

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.[8]

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.[8] 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.[8] Salacia and Actaea will next occult each other in 2067.[8]

Name

This minor planet was named after Salacia (/səˈleɪʃə/), the goddess of salt water and the wife of Neptune.[2] Naming citation was published on 18 February 2011 (M.P.C. 73984).[15]

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

Planetary symbols are no longer much used in astronomy, so Salacia never received a symbol in the astronomical literature. There is no standard symbol for Salacia used by astrologers either. Denis Moskowitz, a software engineer in Massachusetts who designed the symbols for most of the dwarf planets, proposed a stylised hippocamp () as the symbol for Salacia, befitting Salacia as Neptune's consort.[16]

See also

• List of Solar System objects by size

Notes

References

External links

• (120347) Salacia at Johnston's Archive
• Salacia: As big as Ceres, but much farther away (Emily Lakdawalla – 2012/06/26)
• 120347 Salacia at the JPL Small-Body Database
  • Close approach · Discovery · Ephemeris · Orbit diagram · Orbital elements · Physical parameters

На других языках

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[de] (120347) Salacia

(120347) Salacia (frühere Bezeichnung 2004 SB60) ist ein großes transneptunisches Objekt im Kuipergürtel, das bahndynamisch als Cubewano oder als erweitertes Scattered Disc Object (DO) eingestuft wird. Aufgrund seiner Größe ist der Asteroid ein Zwergplanetenkandidat. Da Salacia über einen großen Begleiter namens Actaea verfügt, kann dieses System auch als Doppelasteroidensystem verstanden werden.

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- [en] 120347 Salacia

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[ru] (120347) Салация

Салация (120347 Salacia по каталогу Центра малых планет[3]) — транснептуновый объект, расположенный в поясе Койпера. Классифицируется и как кьюбивано (MPC)[4], и как отделённый объект (DES)[5]. Он был обнаружен 22 сентября 2004 года группой учёных из Паломарской обсерватории. Обладает одним из самых низких значений альбедо среди крупных ТНО. Майкл Браун считает его кандидатом на статус карликовой планеты. По оценке М. Брауна, при альбедо 4 % и абсолютной магнитуде 4,2 диаметр объекта составляет 921 км[6].

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