Sycorax (moon)

Sycorax
Discovery pictures from Sycorax, 1997
Provisional or systematic name	S / 1997 U 2
Central body	Uranus
Properties of the orbit
Major semi-axis	12,175,560 km
Periapsis	5,957,740 km
Apoapsis	18,393,380 km
eccentricity	0.5106803
Orbit inclination	152.49571 °
Orbital time	1283.48 d
Mean orbital velocity	0.69 km / s
Physical Properties
Albedo	≈ 0.04-0.07
Apparent brightness	20.8 mag
Medium diameter	≈ 150 km
Dimensions	≈ 2.3 · 10 18 kg
surface	≈ 70,000 km 2
Medium density	≈ 1.3-1.5 g / cm 3
Sidereal rotation	0.1542 days (3.7 h)
Acceleration of gravity on the surface	0.040 m / s 2
Surface temperature	≈ −184 to −208 ° C; 89-65 K
discovery
Explorer	Brett J. Gladman , Philip D. Nicholson , Joseph A. Burns , John J. Kavelaars
Date of discovery	September 6, 1997
Remarks	Physical data relatively imprecise
Size comparison of irregular moons in the solar system, including Sycorax

Sycorax (also Uranus XVII ) is the fifth outermost of the 27 known and the fifth innermost of the outer retrograde irregular moons of the planet Uranus . It is the largest of the planet's irregular natural satellites.

Discovery and naming

Sycorax was photographed on the night of September 6-7, 1997 by a team of astronomers Philip D. Nicholson , Joseph A. Burns and John J. Kavelaars on the same night as the second largest known irregular Uranus moon Caliban . The images were taken with the 5-meter reflector telescope at the Hale Observatory in California ( USA ). The actual discovery was made by team member Brett J. Gladman in early October, who tracked down both moons on the images. Sycorax and Caliban were the first irregular moons on the planet to be discovered. The discovery was announced on April 30, 1998; the moon was initially given the provisional designation S / 1997 U 2 at the end of October 1997 .

In 1999, at the suggestion of Brett Gladman, Phil Nicholson, Joseph Burns, JJ Kavelaars, Brian Geoffrey Marsden , Gareth V. Williams and Warren B. Offutt, the moon was given the official name Sycorax, like all irregular Uranus moons except Margaret after a figure in William Shakespeare's comedy The Tempest . Sycorax was a witch who had died before the action began. She was banished to the island in the Mediterranean , where she gave birth to Caliban and where Prospero was later banished. She was responsible for the unjust capture and enslavement of the air spirit Ariel , who was later freed by Prospero.

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 / 1997 U 2 corresponds to the system of the International Astronomical Union (IAU).

Track properties

Classification in the irregular moons

Orbit

Sycorax orbits Uranus on a retrograde , strongly elliptical orbit between 5,957,740 and 18,393,380 km from its center ( major orbit half-axis 12,175,560 km or 476,371 Uranus radii), i.e. around 12,150,000 km above its cloud ceiling. The orbital eccentricity is 0.5106803, the web is 152.49571 ° relative to the ecliptic inclined . Sycorax is almost 21 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). According to calculations by a Russian astronomer, the inclination of the orbit has changed by around 7 ° and the eccentricity by around 10%. The eccentricity is therefore also given between 0.5219 and 0.5224, the orbit inclination (compared to the ecliptic) between 152.456 ° and 159.420 ° and the major orbit half-axis with 12.1794 million km. Due to its high eccentricity, Sycorax comes closer to Uranus in its periapsis than the three further inward orbiting moons Caliban , Stephano and Trinculo .

Sycorax is the largest and eponymous 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 Prospero , Setebos and Ferdinand also belong. However, Sycorax has a much redder color than the other moons in the group, which are more gray in color.

The orbit of the nearest inner moon Trinculo is on average about 3.67 million km from the orbit of Sycorax, the distance of the orbit of the next outer moon Margaret is on average about 2.24 million km.

Sycorax orbits Uranus in around 1283 days, 11 hours and 31 minutes, or around 3.514 earth years. The orbital period is also given as 1288.28 and 1288.38 days. Sycorax needs almost as long to orbit Uranus as the asteroid Vesta around the sun.

rotation

The Sycorax light curve indicates a rotation of between 3 hours and 42 minutes (3.7 h ) and 4 hours and 6 minutes (4.1 h).

Physical Properties

Sycorax has an estimated diameter of 150 km (according to other data 190 km), based on the assumed reflectivity 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 0.040 m / s ² , which corresponds to about 0.4% of that on earth.

surface

Almost nothing is known about the surface of Sycorax. According to some reports, it has a reddish appearance, redder than Jupiter's moon Himalia or the Sun, but less red than most Kuiper belt objects . Sycorax may also be a little less red than the second largest irregular Uranus moon, Caliban , which indicates a different origin. In general, it is similar in color to the trans-Neptunian objects like Pluto and others, but in contrast to them, reflects less light. In the near infrared , the spectrum becomes blue between wavelengths of 0.8 to 1.25 meters and finally neutral at longer wavelengths.

Emergence

Sycorax is believed to be a trapped object of the Kuiper Belt and not originated 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 Sycorax belongs to the same dynamic group as Setebos and Prospero , and therefore these moons likely have a common origin.

exploration

Due to the great distance to Uranus and the weak brightness of 20.8 mag, which is 1: 1300000 compared to the central planet, Sycorax was not found when the Voyager 2 space probe flew by in 1986. Since its discovery in 1997, Sycorax could only be observed through earth-based telescopes and its orbital elements and their brightness could be determined.

Web links

• IAUC 6764: Satellites of Uranus October 31, 1997 (discovery)
• IAUC 6869: S / 1997 U 2 April 7, 1998 (rediscovery)
• IAUC 7132: Satellites of Uranus March 27, 1999 (numbering and naming)
• Polish moon page: Sycorax description and further links (English)
• Discovery of two distant irregular moons of Uranus April 30, 1998 (discovery report )
• Update on New Satellites of Uranus February 2000 (proposed name)

Individual evidence

1. ^ IAU: Natural Satellites Ephemeris Service. IAU Minor Planet Center, accessed February 11, 2011 . 
2. ^ M. Maris, G. Carraro, G. Cremonese, M. Fulle: Multicolor Photometry of the Uranus irregular satellites Sycorax and Caliban. Iopscience, accessed February 11, 2011 . 
3. ↑ Richard W. Schmude, jr .: Uranus, Neptune, Pluto and how to observe them. Springer, accessed February 12, 2011 .