Setebos (moon)

John J. Kavelaars, Brett J. Gladman, Matthew J. Holman, Jean -Marc Petit, Hans Scholl

Setebos (also Uranus XIX) is the twenty-sixth of the 27 known and the eighth of the outer irregular satellites of the planet Uranus. He is one of the smaller natural satellite of the planet.

Discovery and designation

Setebos was discovered on July 18, 1999 a team of astronomers John J. Kavelaars, Brett J. Gladman, Matthew J. Holman, Jean -Marc Petit and Hans Scholl on photographic images together with the Uranian moons Stephano and Prospero. The recordings were made by the 3.6-meter Canada -France - Hawaii Telescope on Mauna Kea in Hawaii (USA). The discovery was announced on 27 July 1999; the moon first received the provisional designation S/1999 U 1

On 21 August 2000 the moon will then receive the official name of Setebos, like all irregular moons of Uranus except Margaret, after a figure in William Shakespeare's The Tempest. Setebos is a deity from South America (Patagonia, Argentina), which is worshiped by the witch Sycorax and her son, the monster Caliban.

So far, all the moons of Uranus are named after characters from Shakespeare or Alexander Pope. The first four moons discovered Uranus ( Oberon, Titania, Ariel, Umbriel ) were proposed by John Herschel, the son of Uranus discoverer William Herschel, named. Later, the tradition of naming was retained.

The provisional designation S/1999 U 1 corresponds to the classification of the International Astronomical Union ( IAU).

Web properties

Setebos Uranus rotates on a retrograde, highly elliptical orbit 7451800-27386730 km from its center ( Large semi-major axis 17,419,270 km or 681.532 Uranus radii ), or about 17.3937 million km on whose cloud tops. The orbital eccentricity is 0.572209, the orbit is inclined 145.8835 ° from the ecliptic. Setebos times as far from just under 30 of Uranus as the outermost regular moon Oberon.

Due to the large distance to Uranus and gravitational disturbances caused by the sun and other factors, the orbital parameters are thus possibly variable; the moon could perhaps get ( back ) into a heliocentric orbit. The eccentricity is therefore 0.5843 to 0.5914, the orbital inclination ( with respect to the ecliptic ) between 158.161 and 158.235 ° ° and the Great semi-major axis between 17,418 und 17.501 million kilometers indicated.

Setebos is a member of Sycorax group, a subgroup of the irregular moons with very high eccentricity and high orbital inclinations of 140 to 170 °, which also Sycorax, Prospero and Ferdinand belong.

The orbit of the next inner moon Prospero is removed an average of 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 kilometers.

Setebos revolves around Uranus in 2196 days 8 hours and 24 minutes or about 6,013 Earth years. The orbital period is also specified with 2225.08 to 2234.77 days. Setebos thus requires more than half of the orbital period of the planet Jupiter around the Sun to orbit Uranus.

Physical Properties

Setebos has a diameter estimated at 47 km ( according to other sources 48 km), based on the assumed for him albedo of 4 %, which may be as well as 7%. The surface is thus in any case very dark. Its density is estimated to be between 1.3 and 1.5 g/cm3. So the moon is likely to be composed predominantly of water ice and silicate rock. On its surface, the gravitational acceleration is 0.0063 m/s2, corresponding to about 6 ‰ of the earth. Setebos appears in the spectrum in gray.

Formation

It is believed that Setebos is a captured Kuiper belt object and is not in the accretion disk that formed the Uranus system, created. It is conceivable that the moon of a Kuiper Belt object first became a centaur and was subsequently captured by Uranus. The exact trapping mechanism is not known, but the entrapment of a moon requires the dissipation of energy. The hypotheses range from withdrawal of gas from the protoplanetary disk, interactions within the framework of the multi- body problem and capture by the strongly growing mass of Uranus. The orbital parameters suggest that Setebos belongs to the same group dynamic as Sycorax and Prospero and these moons therefore likely to have a common origin.

Research

Because of the great distance to Uranus and weak brightness of 23.3 like the 1:13200000 is opposite to the central planet, Setebos was 2 1986 not found during the flyby of the Voyager spacecraft. Since the discovery in 1999 Setebos could only be observed by ground-based telescopes, while its orbital elements and its brightness can be determined.

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