Sycorax (moon)

Sycorax (/ˈsɪkəræks/ SIK-or-aks) is the largest retrograde irregular satellite of Uranus. Sycorax was discovered on 6 September 1997 by Brett J. Gladman, Philip D. Nicholson, Joseph A. Burns, and John J. Kavelaars using the 200-inch Hale telescope, together with Caliban, and given the temporary designation S/1997 U 2.^[1]

Retrogade irregular satellites of Uranus

Officially confirmed as Uranus XVII, it was named after Sycorax, Caliban's mother in William Shakespeare's play The Tempest.

Orbit

Sycorax follows a distant orbit, more than 20 times further from Uranus than the furthest regular moon, Oberon.^[1] 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 common origin.^[8]

The diagram illustrates the orbital parameters of the retrograde irregular satellites of Uranus (in polar co-ordinates) 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 150 km (assuming an albedo of 0.04),^[4][5] making it the largest irregular satellite of Uranus, comparable in size with Puck and with Himalia, the biggest irregular satellite of Jupiter.

The satellite appears light-red in the visible spectrum (colour indices B–V = 0.87 V–R = 0.44,^[9] B–V = 0.78 ± 0.02 V–R = 0.62 ± 0.01,^[8] B–V = 0.839 ± 0.014 V–R = 0.531 ± 0.005^[6]), 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.^[7]

The rotation period of Sycorax is estimated at about 3.6 hours. Rotation causes periodical variations of the visible magnitude with the amplitude of 0.07.^[6]

Origin

Sycorax is hypothesized to be a captured object: it did not form in the accretionary disk, which existed around Uranus just after its formation. The exact capture mechanism is not known, but capturing a moon requires the dissipation of energy. The possible capture processes include: gas drag in the protoplanetary disk, many-body interactions and the capture during the fast growth of the Uranus's mass (so called pull-down).^[10][6]

See also

• Moons of Uranus
• Irregular moons

References

• Gladman, B. J.; Nicholson, P. D.; Burns, J. A.; Kavelaars, J. J.; Marsden, B. G.; Williams, G. V.; Offutt, W. B. (1998). "Discovery of two distant irregular moons of Uranus". Nature 392 (6679): 897–899. Bibcode:1998Natur.392..897G. doi:10.1038/31890. 
• Grav, Tommy; Holman, Matthew J.; Fraser, Wesley C. (2004-09-20). "Photometry of Irregular Satellites of Uranus and Neptune". The Astrophysical Journal 613 (1): L77–L80. arXiv:astro-ph/0405605. Bibcode:2004ApJ...613L..77G. doi:10.1086/424997. 
• Sheppard, S. S.; Jewitt, D.; Kleyna, J. (2005). "An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness". The Astronomical Journal 129: 518. doi:10.1086/426329. 
• Rettig, T. W.; Walsh, K.; Consolmagno, G. (December 2001). "Implied Evolutionary Differences of the Jovian Irregular Satellites from a BVR Color Survey". Icarus 154 (2): 313–320. Bibcode:2001Icar..154..313R. doi:10.1006/icar.2001.6715. 

External links

Wikimedia Commons has media related to Sycorax (moon).

• Sycorax Profile (by NASA's Solar System Exploration)
• David Jewitt pages
• Uranus' Known Satellites (by Scott S. Sheppard)
• MPC: Natural Satellites Ephemeris Service

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