Prospero (moon)

Prospero
Sequence of images from the discovery of Prospero, 1999
Provisional or systematic name	S / 1999 U 3
Central body	Uranus
Properties of the orbit
Major semi-axis	16,162,240 km
Periapsis	10,834,570 km
Apoapsis	21,489,900 km
eccentricity	0.3296367
Orbit inclination	146.01704 (ecliptic) °
Orbital time	1962.95 d
Mean orbital velocity	0.60 km / s
Physical Properties
Albedo	≈ 0.04-0.07
Apparent brightness	23.2 mag
Medium diameter	≈ 50 km
Dimensions	≈ 2.1-8.5 · 10 16 kg
surface	≈ 8,000 km 2
Medium density	≈ 1.3-1.5 g / cm 3
Acceleration of gravity on the surface	0.0063 m / s 2
Surface temperature	≈ −184 to −208 ° C; 89-65 K
discovery
Explorer	Matthew J. Holman , John J. Kavelaars , Brett J. Gladman , Jean-Marc Petit , Hans Scholl
Date of discovery	July 18, 1999
Remarks	Physical data relatively imprecise

Prospero (also Uranus XVIII ) is the twenty-fifth innermost of the 27 known and the seventh of the outer irregular moons of the planet Uranus . It is one of the smaller natural satellites on the planet.

Discovery and naming

Prospero was discovered on July 18, 1999 by a team consisting of the astronomers Matthew J. Holman , John J. Kavelaars , Brett J. Gladman , Jean-Marc Petit and Hans Scholl on photographic recordings together with the Uranus moons Stephano and Setebos . The recordings were made with the 3.6 meter Canada-France-Hawaii Telescope on Mauna Kea in Hawaii ( USA ). The discovery was announced on September 4, 1999; the moon was initially given the provisional designation S / 1999 U 3 .

On August 21, 2000, the moon was officially named Prospero, like all irregular Uranus moons except Margaret after a character in William Shakespeare's comedy The Storm . The magician Prospero was the rightful Duke of Milan . His brother Antonio , with the help of Alonso , King of Naples , seized power in the duchy . Prospero was forced to flee to an island in the Mediterranean with his daughter Miranda , where he perfected his magical powers in order to regain his duchy. He caused Alonso and Antonio to be shipwrecked on his island. He was finally reconciled with them and again became master of his duchy.

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 / 1999 U 3 corresponds to the system of the International Astronomical Union (IAU).

Track properties

Classification in the irregular moons

Prospero orbits Uranus on a retrograde , relatively strongly elliptical orbit between 10,834,570 and 21,489,900 km from its center ( major orbit half-axis 16,162,240 km or 632,350 Uranus radii), i.e. around 16,136,700 km above its cloud ceiling. The orbit eccentricity is 0.3296367, the orbit is 146.01704 ° inclined to the ecliptic . Prospero is almost 28 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 0.4431 and 0.4448, the orbit inclination (with respect to the ecliptic) between 151.83 ° and 152.0 ° and the major orbit half-axis between 16.2430 and 16.2768 million km.

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

The orbit of the next inner moon Margaret is on average about 1.74 million km from Prospero's orbit, the distance of the orbit of the next outer moon Setebo is on average about 1.26 million km.

Prospero orbits Uranus in around 1962 days, 22 hours and 48 minutes, or around 5,374 earth years. The orbital period is also given as 1977.0 and 1978.37 days. Prospero needs about 9 months longer to orbit Uranus than the dwarf planet Ceres around the sun.

Physical Properties

Prospero has an estimated diameter of 50 km (according to other information 30 km), based on the assumed reflectivity of 4%, which, however, can also be 7%. In any case, the surface is extremely dark. Its 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 0.0063 m / s ² , which corresponds to about 6 per thousand of that on earth. Prospero appears in the spectrum in gray color.

Emergence

Prospero is believed to be a trapped object of the Kuiper Belt and not arose in the accretion disk that formed the uranium 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. The orbital parameters indicate that Prospero belongs to the same dynamic group as Sycorax and Setebos , and therefore these moons likely have a common origin.

exploration

Due to the great distance to Uranus and the weak brightness of 23.2 mag, which is 1: 7600000 compared to the central planet, Prospero was not found when the Voyager 2 space probe flew by in 1986. Since its discovery in 1999, Prospero could only be observed through earth-based telescopes and its orbital elements and its brightness could be determined.

Web links

• IAUC 7248: Probable new Satellites of Uranus September 4, 1999 (discovery)
• IAUC 7447: S / 1999 U 3 April 7, 1998 (rediscovery)
• IAUC 7479: Satellites of Uranus August 21, 2000 (designation)
• Polish moon page: Prospero description and further links (English)

Individual evidence

1. ^ IAU: Natural Satellites Ephemeris Service. IAU Minor Planet Center, accessed February 11, 2011 .