Setebos (moon)
| Setebos | |
|---|---|
|
|
| Discovery picture of Setebos | |
| Provisional or systematic name | S / 1999 U 1 |
| Central body | Uranus |
| Properties of the orbit | |
| Major semi-axis | 17,419,270 km |
| Periapsis | 7,451,800 km |
| Apoapsis | 27,386,730 km |
| eccentricity | 0.5722090 |
| Orbit inclination | 145.88350 (ecliptic) ° |
| Orbital time | 2196.35 d |
| Mean orbital velocity | 0.57 km / s |
| Physical Properties | |
| Albedo | ≈ 0.04-0.07 |
| Apparent brightness | 23.3 mag |
| Medium diameter | ≈ 47 km |
| Dimensions | ≈ 2.1-7.5 · 10 16 kg |
| surface | ≈ 7,200 km 2 |
| Medium density | ≈ 1.3-1.5 g / cm 3 |
| Acceleration of gravity on the surface | 0.0063 m / s 2 |
| Escape speed | 20.4 m / s |
| Surface temperature | ≈ −184 to −208 ° C; 89-65 K |
| discovery | |
| Explorer |
John J. Kavelaars , |
| Date of discovery | July 18, 1999 |
| Remarks | Physical data relatively imprecise |
Setebos (also Uranus XIX ) is the second outermost of the 27 known and the eighth innermost of the outer irregular moons of the planet Uranus . It is one of the smaller natural satellites on the planet.
Discovery and naming
Setebos was discovered on July 18, 1999 by a team consisting of the astronomers John J. Kavelaars , Brett J. Gladman , Matthew J. Holman , Jean-Marc Petit and Hans Scholl together with the Uranus moons Stephano and Prospero . The recordings were made with the 3.6 meter Canada-France-Hawaii Telescope on Mauna Kea in Hawaii ( USA ). The discovery was announced on July 27, 1999; the moon was initially given the provisional designation S / 1999 U 1 .
On August 21, 2000, the moon was given the official name Setebo, like all irregular Uranus moons except Margaret after a character in William Shakespeare's comedy The Tempest . Setebos is a deity from South America ( Patagonia , Argentina ) who is worshiped by the witch Sycorax and her son, the monster Caliban .
So far, all Uranus moons have been named after characters from Shakespeare or Alexander Pope . The first four Uranus moons discovered ( Oberon , Titania , Ariel , Umbriel ) were named after suggestions by John Herschel , the son of the Uranus discoverer Wilhelm Herschel . Later the tradition of naming was retained.
The provisional designation S / 1999 U 1 corresponds to the system of the International Astronomical Union (IAU).
Track properties
Setebos orbits Uranus in a retrograde , strongly elliptical orbit between 7,451,800 and 27,386,730 km from its center ( major orbit half-axis 17,419,270 km or 681,532 Uranus radii), i.e. around 17,393,700 km above its cloud ceiling. The orbital eccentricity is 0.572209, the web is 145.8835 ° relative to the ecliptic inclined . Setebos is almost 30 times as far from Uranus as the outermost regular moon Oberon .
Due to the great distance to Uranus and gravitational disturbances from the sun and other factors, the orbit parameters are possibly variable; the moon could perhaps also enter a heliocentric orbit (again). The eccentricity is therefore also given between 0.5843 and 0.5914, the orbit inclination (with respect to the ecliptic) between 158.161 ° and 158.235 ° and the major orbit half-axis between 17.418 and 17.501 million km.
Setebos is a member of the Sycorax group , a subgroup of the irregular moons with very high eccentricity and high orbital inclinations between 140 ° and 170 °, to which Sycorax , Prospero and Ferdinand also belong.
The orbit of the next inner moon Prospero is on average about 1.26 million km from the orbit of Setebos, the distance of the orbit of the outermost Uranus moon Ferdinand is on average about 3.09 million km.
Setebos orbits Uranus in around 2196 days, 8 hours and 24 minutes, or around 6,013 earth years. The orbital period is also given as 2225.08 to 2234.77 days. Setebos therefore needs more than half the orbit time of the planet Jupiter around the sun for one orbit around Uranus .
Physical Properties
Setebos has an estimated diameter of 47 km (according to other information 48 km), based on the assumed reflectivity of 4%, which, however, can also be 7%. In any case, the surface is extremely dark. Its density is estimated to be between 1.3 and 1.5 g / cm 3 . The moon is therefore likely to be composed mainly of water ice and silicate rock. On its surface, the acceleration due to gravity is 0.0063 m / s 2 , which corresponds to about 6 ‰ of that on earth. Setebos appears in the spectrum in gray.
Emergence
Setebos are believed to be a trapped object of the Kuiper Belt and not originated in the accretion disk that formed the uranium system. It is conceivable that the moon first went from a Kuiper belt object to a centaur and was then captured by Uranus. The exact trapping mechanism is unknown, but trapping a moon requires dissipating energy. The hypotheses range from the entry of gas into the protoplanetary disk , interactions in the context of the multibody problem and capture by the rapidly increasing mass of Uranus. The orbital parameters indicate that Setebos belongs to the same dynamic group as Sycorax and Prospero , and therefore these moons likely have a common origin.
exploration
Due to the great distance to Uranus and the weak brightness of 23.3 mag, which is 1: 13200000 compared to the central planet, Setebos was not found when the Voyager 2 space probe flew by in 1986. Since its discovery in 1999, Setebos could only be observed through earth-based telescopes and its orbital elements and its brightness could be determined.
Web links
- IAUC 7230: Probable new Satellites of Uranus July 27, 1999 (discovery)
- IAUC 7248: Probable new Satellites of Uranus September 4, 1999 (discovery)
- IAUC 7450: S / 1999 U 1 July 8, 2000 (rediscovery)
- IAUC 7479: Satellites of Uranus August 21, 2000 (designation)
- Polish moon page: Setebo's description and further links (English)
Individual evidence
- ^ IAU: Natural Satellites Ephemeris Service. IAU Minor Planet Center, accessed February 11, 2011 .