Sao (moon)
| Sao | |
|---|---|
| Provisional or systematic name | S / 2002 N 2 |
| Central body | Neptune |
| Properties of the orbit | |
| Major semi-axis | 22,182,010 km |
| Periapsis | 19,054,600 km |
| Apoapsis | 25,309,430 km |
| eccentricity | 0.1409888 |
| Orbit inclination to the equator of the central body | 65.22 ° |
| Orbit inclination to the ecliptic | 52.85491 ° |
| Orbital time | 2905.69 d |
| Mean orbital velocity | 0.55 km / s |
| Physical Properties | |
| Albedo | ≈ 0.16 |
| Apparent brightness | 25.4 mag |
| Medium diameter | ≈ 44 km |
| Dimensions | ≈ 8.9920 · 10 16 kg |
| Medium density | ≈ 1.5 g / cm 3 |
| Acceleration of gravity on the surface | ≈ 0.010 m / s 2 |
| discovery | |
| Explorer |
Matthew J. Holman et al. |
| Date of discovery | August 14, 2002 |
Sao (also Neptune XI ) is the fourth outermost moon on the planet Neptune . It is one of Neptune's prograde irregular moons .
Discovery and naming
Sao was founded on August 14, 2002 by a team consisting of Matthew J. Holman , John J. Kavelaars , Tommy Grav , Brett J. Gladman , Wesley C. Fraser, Dan Milisavljevic, Philip D. Nicholson, Joseph A. Burns, Valerio Carruba , Jean-Marc Petit, Philippe Rousselot, Oliver Mousis, Brian G. Marsden and Robert A. Jacobson discovered on recordings from August 14 to September 4, 2002 and August 10, 2001 together with Halimede and Laomedeia . The recordings were made by the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile and the 3.6-meter Canada-France-Hawaii Telescope in Hawaii . Several images were digitally combined until the moons, in contrast to the line-shaped stars, appeared point-like. The discovery was announced on January 13, 2003; the moon was initially given the provisional designation S / 2002 N 2 .
On February 3, 2007, the moon was named after Sao (Greek for "the rescuer"), one of the 50 or so Nereid sea nymphs from Greek mythology . They are the beautiful daughters of the wise old man Nereus , who was said to be prophecy and constant metamorphosis, and his wife, the Oceanid Doris . Sao was associated with sailing.
Track properties
Sao orbits Neptune on a prograde , elliptical orbit between 19,054,600 and 25,309,430 km from its center (major orbit half-axis 22,182,010 or 895.736 Neptune radii). The orbital eccentricity is 0.1409888, the orbit is 65.22 ° inclined to the equator of Neptune . The moon is in a so-called Kozai orbital resonance , which means that its orbital inclination and eccentricity are coupled to each other (the orbital inclination decreases when the eccentricity increases, and vice versa). It can therefore be assumed that these parameters are variable, since the eccentricity is also given as 0.2931, the orbit inclination (compared to the ecliptic ) with 48.511 ° and the major orbit half-axis between 22.228 and 22.422 million km.
The orbit of the next inner moon Halimede is on average about 5.6 million km from Sao's orbit, the distance of the orbit of the next outer moon Laomedeia is on average about 1.3 million km.
Sao orbit Neptune in around 2,905 days, 15 hours and 22 minutes or around 7,961 earth years, i.e. longer than the four inner planets, the dwarf planet Ceres and most of the asteroids of the main belt around the sun need.
Physical Properties
Sao is estimated to be 44 km in diameter based on its assumed reflectivity of 16%. The surface is therefore relatively dark. Their density is estimated at 1.5 g / cm 3 . This means that the moon is mostly composed of water ice .
The moon is believed to be a trapped asteroid.
exploration
Due to the great distance to Neptune and the weak brightness of 25.4 mag, which is 1: 12000000 compared to the central planet, Sao was not found during the flyby of Voyager 2 in 1989. Since its discovery in 2002, Sao could only be observed through earth-based telescopes and its orbital elements and their brightness could be determined.
Web links
- IAUC 8047: Satellites of Neptune Jan 13, 2003 (discovery)
- IAUC 8802: Satellites of Neptune February 3, 2007 (numbering and naming)
- IAU: Natural Satellites Ephemeris Service IAU: Orbital parameters and ephemeris of irregular moons
- NASA: Planetary Satellite Physical Parameters NASA: Physical Parameters (English)
- NASA: Planetary Satellite Mean Orbital Parameters NASA: Orbital Parameters (English)
- NASA: Neptunian Satellite Fact Sheet NASA: List of Parameters
- Scott S. Sheppard: Neptune's Known Satellites List with parameters of the Neptune system (English)
- USGS: Planet and Satellite Names and Discoverers Names of planets and satellites
- Polish moon page: Sao description and further links (English)