Margaret (moon)
| Margaret | |
|---|---|
| Provisional or systematic name | S / 2003 U 3 |
| Central body | Uranus |
| Properties of the orbit | |
| Major semi-axis | 14,345,000 km |
| Periapsis | 4,862,955 km |
| Apoapsis | 23,827,045 km |
| eccentricity | 0.661 |
| Orbit inclination | 56.6 ° |
| Orbital time | 1694.8 d |
| Mean orbital velocity | 0.62 km / s |
| Physical Properties | |
| Albedo | ≈ 0.04-0.07 |
| Apparent brightness | 25.2 mag |
| Medium diameter | ≈ 20 km |
| Dimensions | ≈ 1.0-5.5 · 10 15 kg |
| surface | ≈ 1,300 km 2 |
| Medium density | ≈ 1.3-1.5 g / cm 3 |
| Acceleration of gravity on the surface | 0.0023 m / s 2 |
| Surface temperature | ≈ −184 to −208 ° C / 89–65 K |
| discovery | |
| Explorer | |
| Date of discovery | August 29, 2003 |
| Remarks | Physical data relatively imprecise |
Margaret (also Uranus XXIII ) is the twenty-fourth of the 27 known and the sixth and only prograde of the outer irregular moons of the planet Uranus .
Discovery and naming
Margaret was discovered on August 29, 2003 by the astronomer Scott S. Sheppard , on recordings by David C. Jewitt and himself. These recordings were made with the 8.2 meter Subaru Reflector Telescope at the Mauna Kea Observatory in Hawaii ( USA ). Actually, the moon could already be seen on August 13 and 25, 2001 by Matthew J. Holman and John J. Kavelaars on recordings with the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile , on which Francisco was also able to see , Trinculo and Ferdinand could be observed. However, no orbit could be calculated on the basis of the data obtained and the two astronomers did not recognize that it was a previously unknown moon, as they believed Margaret to be one of the moons that had already been discovered. The discovery was announced on October 9, 2003; the moon was initially given the provisional designation S / 2003 U 3 .
On December 29, 2005, the moon was officially named Margaret, as the only irregular moon after a character in William Shakespeare's comedy Much Ado About Nothing . Margaret was a maid of the hero who was mistaken for Hero , Leonato's daughter , when she entertained Boracchio at Hero's window; this led to a great embarrassment at Hero's wedding to Count Claudio .
Margaret was also the name of Reignier's daughter and later wife of King Henry VI. from Shakespeare's Henry VI.
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 / 2003 U 3 corresponds to the system of the International Astronomical Union (IAU).
Track properties
Margaret orbits Uranus on a prograde , very elliptical orbit between 4,862,955 and 23,827,045 km from its center ( major orbit half-axis 14,345,000 km or 561.3 Uranus radii), i.e. around 14,470,100 km above its cloud ceiling. The orbital eccentricity is 0.661; the orbit is inclined 56.6 ° to the ecliptic . Margaret is almost 25 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 0.6608 and 0.6772, the orbit inclination (compared to the ecliptic) between 51.455 ° and 57.367 ° and the major orbit half-axis between 14.1767 and 14.3450 million km. Due to the very high eccentricity for a moon - which according to current knowledge is the second highest in the solar system after that of the Neptune moon Nereid - Margaret Uranus comes closer in her periapsis than the four irregular moons Caliban , Stephano , Trinculo and Sycorax, which circle further inside .
Margaret is the only one of the outer irregular Uranus moons with a prograde orbit, i.e. that is, the moon moves around the planet in the direction of rotation of Uranus. It is therefore definitely not a member of the Sycorax group , a group of moons with orbital inclinations between 140 and 170 °. Margaret thus forms a separate group. All of the other eight outer irregular moons show retrograde orbits.
The orbit of the next inner moon Sycorax is on average about 2.24 million km from Margaret's orbit, the distance of the orbit of the next outer moon Prospero is on average about 1.74 million km.
Margaret orbits Uranus in around 1694 days and 19 hours or around 4.64 earth years. The orbital period is also given as 1661.0 and 1687.01 days. Margaret needs almost as long to orbit Uranus as the dwarf planet Ceres around the sun.
Physical Properties
Margaret has an estimated diameter of 20 km (according to other data 22 km), based on the assumed retroreflective power of 4%, which, however, can also be 7%. In any case, the surface is extremely dark. Their 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 0.0023 m / s 2 , which corresponds to about 2 ‰ of that on earth. Margaret appears in the spectrum in gray color.
Emergence
Margaret is believed to be a trapped object of the Kuiper Belt and not arose in the accretion disk that formed the Uranus 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.
exploration
Due to the great distance to Uranus and the weak magnitude of 25.2 mag, which is 1: 76,000,000 compared to the central planet, Margaret was not found when the Voyager 2 space probe flew by in 1986. Since the discovery in 2003 Margaret could only be observed through terrestrial telescopes and her orbital elements and their brightness could be determined.
Web links
- IAUC 8217: S / 2003 U 3 October 9, 2003 (discovery)
- IAUC 8648: Satellites of Uranus December 29, 2005 (numbering and naming)
- Polish moon page: Margaret description and further links (English)
Individual evidence
- ↑ Uranus' known satellites (Engl.)
- ^ IAU: Natural Satellites Ephemeris Service. IAU Minor Planet Center, accessed February 12, 2011 .