Margaret (moon)

Scott S. Sheppard David C. Jewitt

Margaret (also Uranus XXIII ) is the twenty-fourth of the 27 known and the sixth and only prograde irregular moons of the outer planets Uranus. He is the moon with the largest previously known orbital eccentricity in the solar system.

Discovery and designation

Margaret was discovered by the astronomer Scott S. Sheppard, David C. Jewitt on photographs of him and even, on 29 August 2003. These images were taken with the 8.2-meter Subaru Telescope on Mauna Reflector Kea Observatory in Hawaii (USA). Actually, the moon could be seen on pictures with the 4.0 -meter Blanco telescope on 13 and 25 August 2001 by Matthew J. Holman and John J. at Cerro Tololo Inter- Kavelaars American Observatory in Chile, where also Francisco, Trinculo and Ferdinand could be observed. However, no path could be calculated from the data obtained and the two astronomers did not realize that it was a previously unknown moon, and there they mourned Margaret for one of the already discovered moons. The discovery was announced on 9 October 2003; the moon first received the provisional designation S/2003 U 3

On 29 December 2005 the moon has then received the official name of Margaret, the only irregular moon after a figure in William Shakespeare's comedy Much Ado About Nothing. Margaret was a maid of the hero, who was with Hero, daughter of Leonato, confused, as she talked to Boracchio Heros window; this resulted in a major embarrassment to Heros marriage to Count Claudio.

Margaret was also the name of the daughter Reigniers and later wife of King Henry VI. from Shakespeare's Henry VI.

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/2003 U 3 corresponds to the classification of the International Astronomical Union ( IAU).

Web properties

Margaret Uranus rotates on a prograde, highly elliptical orbit 2913700-25926970 km from its center ( Large semi-major axis 14,420,340 km or 564.198 Uranus radii ), or about 14.3948 million km on whose cloud tops. The orbital eccentricity of 0.7979451, the orbit is inclined 51.45588 ° from the ecliptic. Margaret is almost 25 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 0.6608 to 0.6772, the orbital inclination ( with respect to the ecliptic ) between 51 455 ° and 57.367 ° and the Great semi-major axis between 14,1767 und 14.345 million kilometers indicated. By a moon extremely high eccentricity - which is the highest according to the current state of knowledge in the solar system, even higher than that of Neptune moon Nereid - comes Margaret Uranus closer in its periapsis than five further inside circular irregular moons Francisco, Caliban, Stephano, Trinculo and Sycorax ( ).

Margaret is the only of the outer irregular moons of Uranus with a prograde path, ie, the moon moves in the direction of rotation of Uranus around the planet. He is certainly not a member of Sycorax group, a group of moons with orbital inclinations of 140 to 170 °. Margaret thus forms a separate group. All other outer eight irregular moons have retrograde orbits.

The orbit of the next inner moon Sycorax is on average about 2.24 million kilometers away from Margaret's orbit, the distance of the path of the next outer moon Prospero is on average about 1.74 million kilometers.

Margaret revolves around Uranus in 1654 days 7 hours and 41 minutes or about 4,529 Earth years. The orbital period is also specified with 1661.0 and 1687.01 days. Margaret takes almost as long as the dwarf planet Ceres around the sun to orbit around Uranus.

Physical Properties

Margaret has a diameter estimated at 20 km ( according to other sources 22 km), based on the assumed for them albedo of 4 %, which may be as well as 7%. The surface is thus in any case very dark. Their 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 0.0023 m/s2, this corresponds to about 2 ‰ of the earthly. Margaret appears in the spectrum in gray.

Formation

It is believed that Margaret 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.

Research

Because of the great distance to Uranus and weak brightness of 25.2 like the 1:76000000 is opposite to the central planet, Margaret was 2 1986 not found during the flyby of the Voyager spacecraft. Since the discovery in 2003 Margaret could only be observed by ground-based telescopes, while their orbital elements and their brightness can be determined.

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