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Actaea (moon)

Moon of 120347 Salacia

Field	Value
name	Actaea
image	Salacia and Actaea Keck-NIRC2 brightened.jpg
caption	Salacia and its moon Actaea, imaged by the Keck telescope on 3 August 2010. Actaea is the fainter object to the left of Salacia.
discoverer	Keith S. Noll, Harold F. Levison, Denise C. Stephen, William M. Grundy
discovered	21 July 2006
mpc_name	Salacia I
alt_names	S/2006 (120347) 1
pronounced
adjectives	Actaean
orbit_ref
semimajor	km
eccentricity
period	days
inclination	°
asc_node	°
arg_peri	°
satellite_of
mean_diameter
mass	≈
density	~0.63 g/cm3
sidereal_day	(synchronous)
albedo
spectral_type	V–I =
abs_magnitude

Actaea, formal designation (120347) Salacia I, is the only known moon of the classical Kuiper belt object 120347 Salacia. Its diameter is estimated to be 393 km, which is approximately one-half the diameter of Salacia; thus, Salacia and Actaea are viewed by William Grundy et al. to be a binary system. Assuming that the following size estimates are correct, Actaea is about the fifth-biggest known moon of a trans-Neptunian object, after Charon (1212 km), Dysnomia (615 km), Vanth (443 km), and Ilmarë (403 km).

Discovery and name

It was discovered on 21 July 2006 by Keith S. Noll, Harold Levison, Denise Stephens, and Will Grundy with the Hubble Space Telescope. On 18 February 2011, it was officially named Actaea after the Nereid nymph Actaea.

Orbit

Actaea orbits its primary every at a distance of and with an eccentricity of . 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.

Physical characteristics

The mass of the system is , with Actaea constituting perhaps 4% of this. Actaea is magnitudes fainter than Salacia, implying a diameter ratio of 2.98 for equal albedos. Hence, assuming equal albedos, it has a diameter of . Actaea has the same color as Salacia (V−I = and , respectively), supporting the assumption of equal albedos. 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 be tidally locked. Salacia and Actaea will next occult each other in 2067.

References

(1 October 2023). "Masses and Densities of Dwarf Planet Satellites Measured with ALMA". The Planetary Science Journal.
(1 February 2019). "A stellar occultation by Vanth, a satellite of (90482) Orcus". Icarus.
(2025-07-09). "ALMA submm measurements of the trans-Neptunian binary system satellites Ilmarë, Actaea, Hi'iaka and Namaka". Copernicus Meetings.
(2025). "Synchronous Rotation in the (120347) Salacia-Actaea System".

Info: Wikipedia Source

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120347-salacia astronomical-objects-discovered-in-2006 discoveries-by-denise-c.-stephens moons-of-dwarf-planets trans-neptunian-satellites

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