120347 Salacia

Discovery 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. although this symbol is not widely used. == Orbit and classification ==

's, except for a near opposite longitude of ascending node. Its current position is near its most northern position above the ecliptic. Orbital characteristics Salacia orbits the Sun at a distance of 37.7–46.7 AU with a semi-major axis of 42.2 AU, finishing its orbit once every 274.0 years. Salacia is a non-resonant object with a moderate eccentricity of approximately 0.11 and a large inclination of 23.9° with respect to the ecliptic. Classification Classical Kuiper belt object Salacia is located in the classical region of the Kuiper belt (approximately 39–48 AU) from the Sun, therefore, it is classified as a typical member of a classical Kuiper belt object (also known as a "cubewano"). The high orbital inclination of Salacia also makes it a dynamically "hot" member of the classical Kuiper belt. The hot classical Kuiper belt objects are believed to have been scattered by Neptune's gravitational influence when the Solar System was still young. Scattered–extended object Gladman et al. suggested that the large inclination of Salacia's orbit makes it a scattered–extended object in the classification of the Deep Ecliptic Survey but a hot classical Kuiper belt object in the classification system of Gladman et al., which might be from the same population that formed during the outward migration of Neptune. Salacia's orbit is within the parameter space of the Haumea collisional family, however; Salacia is not part of it, as evidenced by its lack of the strong water-ice absorption bands. == Physical characteristics ==

Size, mass and density In 2025, the total mass of the Salacia–Actaea system was estimated to be at , with an average system density of which was estimated in 2019; Salacia itself was estimated to be around 838 km in diameter. Salacia has the lowest albedo of any known large trans-Neptunian object. According to the estimate from 2017 based on an improved thermophysical modelling, the size of Salacia is slightly larger at around 866 km and its density therefore is slightly lower (calculated at with the old mass estimate discussed below). Possible dwarf planet William Grundy et al. describe Salacia as a 'dwarf planet–sized TNO'. They had earlier rejected it as a dwarf planet due to its low estimated density, but backed off that position when they later found out it have a relatively high density of . Salacia's extremely low albedo of 4% remains consistent with a lack of geological activity that is thought to be typical for many dwarf planets. Surface and spectrum Salacia has a dark gray surface with an extremely low albedo of that was measured by Kiss et al. in 2025, and a B-V color index of approximately , which is considered a neutral color. Salacia's infrared spectrum is almost featureless, indicating an abundance of water ice of less than 5% on the surface. Near-infrared spectroscopy by the James Webb Space Telescope (JWST) in 2022 revealed the presence of water ice on Salacia's surface. No signs of volatile ices such as methane were detected in JWST's spectrum of Salacia. Near-infrared spectroscopy that was done by the James Webb Space Telescope (JWST) in 2022 detected that there is amorphous water ice ,crystalline water ice and carbon dioxide ice on Salacia's surface. Other mid to large trans-Neptunian objects such as 307261 Máni, 90482 Orcus and 208996 Achlys also have Salacia's neutral spectrum and has a water ice-rich surface or composition. These objects are all classified as "prominent water" ()-type TNOs according to Wong. Rotation and light curves Salacia exhibits a very low light curve amplitude of only approximately 3%, which means that its brightness does not significantly vary as it rotates, which indicates it is likely spheroidal. Salacia is tidally locked to its moon, meaning the two bodies always show the same face to each other. Actaea orbits Salacia once every . Hence, Salacia rotates once on its axis every . == Binary system ==

Moon Salacia has one known moon, Actaea, that orbits its primary every at a distance of km and with an eccentricity of . It was discovered on 21 July 2006 by Keith Noll, Harold Levison, Denise Stephens and William Grundy with the Hubble Space Telescope. Actaea is probably between and in diameter. That is approximately one-half the diameter of Salacia; thus, Salacia and Actaea are viewed by William Grundy et al. as a binary system. Actaea has an extremely low albedo of just , which is approximately half that of Salacia (). Tidal evolution 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. The ratio of Actaea's semi-major axis to its primary's Hill radius is 0.0023, which is the tightest out of every known trans-Neptunian binary with a calculated orbit. Salacia and Actaea will occult each other the next time in 2067. == See also ==