Caliban (moon)

Brett J. Gladman, Philip D. Nicholson, Joseph A. Burns, John J. Kavelaars

Caliban (also Uranus XVI) is the twentieth of the 27 known and the second is the outer retrograde irregular moons of the planet Uranus. It is the second largest of the irregular natural satellite of the planet.

  • 3.1 surface

Discovery and designation

Caliban was taken on the night of 6 to 7 September in 1997 by a team of astronomers Philip D. Nicholson, Joseph A. Burns, and John J. Kavelaars on photographic images on the same night as the largest known irregular moon Uranus Sycorax. The recordings were made by the 5.0 -meter telescope of the Hale Observatory in California (USA). The actual discovery was made by the team member Brett J. Gladman early October, which tracked both moons on the recordings. Caliban and Sycorax were the first discovered irregular satellites of the planet. The discovery was announced on 30 April 1998; the moon was end of October 1997 the provisional designation S/1997 U initially 1

In 1999, the moon on the proposal by Brett Gladman, Phil Nicholson, Joseph Burns, JJ Kavelaars, Brian Geoffrey Marsden, Gareth V. Williams and Warren B. Offutt back then the official name Caliban obtained, as all irregular moons of Uranus except Margaret, after a figure in William Shakespeare's The Tempest. The wild monster Caliban, son of the witch Sycorax, is the grotesque slave of the magician Prospero show, which was held prisoner on an island of this and even tortured. Caliban is an anagram of canibal ( Cannibal ).

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/1997 U 1 corresponds to the classification of the International Astronomical Union ( IAU).

Web properties

Orbit

Caliban Uranus rotates on a retrograde irregular moon for a relatively slightly elliptical orbit 6599100-7730700 km from its center ( Large semi-major axis 7.1649 million kilometers or 280.329 Uranus radii ), ie approximately 7.139 million kilometers on whose cloud tops. The orbital eccentricity of 0.0789681, the orbit is inclined 139.88509 ° to the ecliptic. The inclination relative to the equator of Uranus is 120.28 °. Caliban is about 12 times as far from 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 0.1590 to 0.1812, the orbital inclination ( with respect to the ecliptic ) between 139.89 ° and 141.529 ° and the Great semi-major axis specified with 7.2311 million kilometers. The orbit of Caliban is surprisingly circular for an irregular moon, the eccentricity is probably the lowest of any irregular moons of Uranus.

Caliban is the largest and eponymous member of the Caliban group, a subgroup of the irregular moons with moderate eccentricity and high orbital inclinations of 140 to 170 °, which also includes Francisco, Stephano and Trinculo are. However, Caliban has a much redder color than the other moons of the group, the more likely to have a gray color.

The orbit of the next inner moon Francisco is in the middle distance, about 4 million km from Caliban's orbit, the distance of the path of the next outer moon Stephano is an average of about 800,000 km.

Caliban orbits Uranus in about 579 days, 9 hours and 22 minutes or about 1,586 Earth years. The orbital period is also specified with 579.73 days. Caliban thus requires longer than the earth to orbit Uranus around the sun.

Rotation

The light curve of Caliban has a rotation of 2 hours and 42 minutes ( 2.7 hours ) and a steeply inclined axis of rotation of 98.732 ° back, making the moon as the orbit would have a declining rotation.

Physical Properties

Caliban has a diameter estimated at 72 km ( according to other sources 96-98 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 acceleration due to gravity is 0.038 m/s2, equivalent to just 0.4% of the earthly.

Surface

Over the surface of Caliban is as good as nothing is known. According to some reports, he has a reddish appearance, red as the Jupiter moon Himalia, but less red than most Kuiper Belt objects. Caliban is possibly a little redder than the largest irregular moon Uranus Sycorax. He also absorbs light at a wavelength of 0.7 microns, and a group of astronomers believe that this was due to water ice, which renewed the surface of Caliban.

Formation

It is believed that Caliban 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 Caliban belongs to the same group dynamic as Stephano and Francisco and these moons therefore likely to have a common origin.

Research

Due to the large distance to Uranus and weak brightness of 22.4 like that is 1:5750000 opposite to the central planet Caliban was 2 1986 not found during the flyby of the Voyager spacecraft. Since the discovery in 1997 Caliban could be observed, while its orbital elements and its brightness can be determined only by ground-based telescopes.

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