Francisco (moon)

John J. Kavelaars, Matthew J. Holman, Dan Milisavljevic, Tommy Grav, Brett J. Gladman

Francisco ( also Uranus XXII) is the nineteenth of the 27 known and the innermost of the outer retrograde irregular moons of the planet Uranus. He is one of the smaller natural satellite of the planet.

Discovery and designation

Francisco was discovered on 13 August 2001 by a team of astronomers Matthew J. Holman, John J. Kavelaars, Dan Milisavljevic and Tommy Grav on photographic shots at about the same time as the outermost known moon Uranus Ferdinand. The recordings were made by the 4.0 -meter Blanco telescope at the Cerro Tololo Inter- American Observatory in Chile. Soon after the shooting, on which Ferdinand, Trinculo and actually Margaret were to be seen, astronomers unfortunately lost the track of the moon again, although three further observations were made. Since the orbit therefore could not be saved, the International Astronomical Union decided not to publish the discovery. It was Brett J. Gladman, who tracked Francisco in September 2003 on recordings from 2002 with the 8.2-meter Very Large Telescope in Chile again. The discovery was announced on 7 October 2003; the moon first received the provisional designation S/2001 U 3

On 29 December 2005 the moon has then received the official name Francisco, like all irregular moons of Uranus except Margaret, after a figure in William Shakespeare's The Tempest. Francisco is a nobleman who has suffered with King Alonso ( the father of Ferdinand ) and other shipwreck. He tried to comfort the king into the alleged loss of his son Ferdinand.

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/2001 U 3 corresponds to the classification of the International Astronomical Union ( IAU).

Web properties

Francisco orbiting Uranus retrograde, for an irregular moon relatively easily elliptical orbit 3690480-4861340 km from its center ( Large semi-major axis 4.27591 million kilometers or 167.296 Uranus radii ), or about 4.25 million km on whose cloud tops. The orbital eccentricity of 0.1369138, the orbit is inclined 147.45993 ° to the ecliptic. Francisco is about 7 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 0.1324 to 0.1459, the orbital inclination ( with respect to the ecliptic ) between 145.22 ° and 147.25 ° and the Great semi-major axis between 4,2760 und 4.2829 million kilometers indicated. The orbit of Francisco is surprisingly circular for an irregular moon, the eccentricity is the lowest of all the irregular moons of Uranus, but with the possible exception of Caliban, vary its information to the eccentricity, however strong.

Francisco is a member of the Caliban group, a subgroup of the irregular moons with moderate eccentricity and high orbital inclinations of 140 to 170 °, to which Caliban, Stephano and Trinculo are.

The orbit of the next inner moon Oberon is an average of 3.7 million km away from Francisco's orbit, the distance of the path of the next outer moon Caliban is, on average, about 4 million km.

Francisco orbits Uranus in about 267 days, 2 hours and 53 minutes or about 0.731 Earth years. The orbital period is also specified with 266.56 and 267.09 days. Francisco takes longer than the planet Venus to orbit Uranus around the sun.

Physical Properties

Francisco has a diameter estimated at 22 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 0.0025 m/s2, this corresponds to about 2 ‰ of the earth. Francisco appears in the spectrum in gray.

Formation

It is believed that Francisco is a captured Kuiper belt object and is not in the accretion disk that formed the Uranus system emerged. 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 Francisco belongs to the same group dynamic as Caliban and Stephano and these moons therefore likely to have a common origin.

Research

Because of the great distance to Uranus and weak brightness of 25.0 like the 1:63100000 is opposite to the central planet, Francisco was 2 1986 not found during the flyby of the Voyager spacecraft. Since the discovery in 2001 and the rediscovery in 2003 Francisco could only be observed by ground-based telescopes, while its orbital elements and its brightness can be determined.

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