Sycorax (moon)
Sycorax is the largest irregular satellite of Uranus, with a diameter of approximately 157 km. It was discovered on 6 September 1997 on the Hale Telescope in California. Sycorax's orbit is retrograde, irregular, and much more distant than that of Oberon, the furthest of Uranus's regular moons. It has been hypothesized that Sycorax is a captured object, as opposed to one that formed with Uranus.
Discovery and Naming
Sycorax was discovered by Brett J. Gladman, Philip D. Nicholson, Joseph A. Burns, and John J. Kavelaars using the 200-inch Hale Telescope, together with Caliban. At the time, it was given the temporary designation S/1997 U 2. Officially confirmed as Uranus XVII, it was named after Sycorax, Caliban's mother in William Shakespeare's play The Tempest. This follows the trend that all Uranian moons are named after Shakespearean characters or those from Alexander Pope's The Rape of the Lock.Orbit
Sycorax follows a distant orbit, more than 20 times further from Uranus than the furthest regular moon, Oberon. Its orbit is retrograde, moderately inclined and eccentric. The orbital parameters suggest that it may belong, together with Setebos and Prospero, to the same dynamic cluster, suggesting a common origin. However, Sycorax has a much redder color than the other moons, which tend to be gray in color.The diagram illustrates the orbital parameters of the retrograde irregular satellites of Uranus with the eccentricity of the orbits represented by the segments extending from the pericentre to the apocentre.
Physical characteristics
The diameter of Sycorax is estimated at 157 km, based on the thermal emission data from Herschel Space telescopes making it the largest irregular satellite of Uranus, comparable in size with Puck and with Himalia, the biggest irregular satellite of Jupiter. At the same time, Sycorax is the seventh largest moon of Uranus.The satellite appears light-red in the visible spectrum, redder than Himalia but still less red than most Kuiper belt objects. However, in the near infrared, the spectrum turns blue between 0.8 and 1.25 μm and finally becomes neutral at the longer wavelengths.
The rotation period of Sycorax is estimated at 6.9 hours. Rotation causes periodical variations of the visible magnitude with the amplitude of 0.12. The rotation axis of Sycorax is unknown, though measurements of its light curve suggest it is being viewed at a near equator-on configuration. In this case, Sycorax may have a north pole right ascension around 356° and a north pole declination around 45°.