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Sycorax
	Animation of discovery images taken by the Hale Telescope in September 1997
Discovery
Discovered by	Philip D. Nicholson; Brett J. Gladman; Joseph A. Burns; John J. Kavelaars;
Discovery site	Hale Telescope at Palomar Obs.
Discovery date	6 September 1997
Designations
Designation	Uranus XVII
Pronunciation	/ˈsɪkɒræks/
Named after	Sycorax
Alternative names	S/1997 U 2
Adjectives	Sycoraxian /sɪkɒˈræksiən/
Orbital characteristics
	Epoch 31 July 2016 (JD 2457600.5)
Observation arc	32.37 yr (11,815 d)
Earliest precovery date	2 June 1984
Semi-major axis	12,193,230 km (0.0815067 AU)
Eccentricity	0.4841889
Orbital period (sidereal)	3.52 yr (1,286.28 d)
Mean anomaly	160.58731°
Mean motion	0° 16m 47.56s / day
Inclination	153.22796° (to the ecliptic); 159.403° (to local Laplace plane)
Longitude of ascending node	258.56478°
Argument of perihelion	16.29680°
Satellite of	Uranus
Physical characteristics
Mean diameter	157+23; −15 km; 165+36; −42 km
Mass	~2.5×1018 kg (estimate)
Mean density	~1.3 g/cm3 (assumed)
Synodic rotation period	6.9162±0.0013 hr (double-peaked); 3.6 hr (single-peaked)
Albedo	0.065+0.015; −0.011; 0.049+0.038; −0.017
Temperature	~65 K (mean estimate)
Apparent magnitude	20.8 (V)
Absolute magnitude (H)	7.5±0.04; 7.83±0.06

Sycorax /ˈsɪkɒræks/ is the largest irregular satellite of Uranus. It was discovered in 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' regular moons. With a diameter of over 150 kilometres (93 mi), it is the largest irregular moon of Uranus. It has been theorized that Sycorax is a captured object, as opposed to one formed with Uranus.

Discovery

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. At the time, it was given the temporary designation S/1997 U 2.^[1] 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.^[11]

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.^[12]

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 165 kilometres (103 mi), based on the thermal emission data from Spitzer and Herschel Space telescopes^[8] 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,^[13] B–V = 0.78 ± 0.02 V–R = 0.62 ± 0.01,^[12] B–V = 0.839 ± 0.014 V–R = 0.531 ± 0.005^[9]), 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^{[clarification needed]} and finally becomes neutral at the longer wavelengths.^[10]

The rotation period of Sycorax is estimated at 6.9 hours.^[7] Rotation causes periodical variations of the visible magnitude with the amplitude of 0.12.^[7] 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°.^[7]

Origin

It is hypothesized that Sycorax is a captured object; it did not form in the accretion disk which existed around Uranus just after its formation. No exact capture mechanism is known, but capturing a moon requires the dissipation of energy. Possible capture processes include gas drag in the protoplanetary disk and many-body interactions and capture during the fast growth of Uranus's mass (so-called pull-down).^[14]^[9]

References

^ ^a ^b ^c Gladman Nicholson et al. 1998.
^ Shakespeare Recording Society (1995) The Tempest (audio CD)
^ Benjamin Smith (1903) The Century Dictionary and Cyclopedia
^ Goldberg (2004) Tempest in the Caribbean
^ "M.P.C. 102109" (PDF). Minor Planet Circular. Minor Planet Center. 14 November 2016.
^ ^a ^b ^c "Planetary Satellite Mean Parameters". Jet Propulsion Laboratory, California Institute of Technology. 2023. Retrieved 2024-08-16.
^ ^a ^b ^c ^d ^e ^f ^g Farkas-Takács, A.; Kiss, Cs.; Pál, A.; Molnár, L.; Szabó, Gy. M.; Hanyecz, O.; et al. (September 2017). "Properties of the Irregular Satellite System around Uranus Inferred from K2, Herschel, and Spitzer Observations". The Astronomical Journal. 154 (3): 13. arXiv:1706.06837. Bibcode:2017AJ....154..119F. doi:10.3847/1538-3881/aa8365. S2CID 118869078. 119.
^ ^a ^b ^c ^d Lellouch, E.; Santos-Sanz, P.; Lacerda, P.; Mommert, M.; Duffard, R.; Ortiz, J. L.; Müller, T. G.; Fornasier, S.; Stansberry, J.; Kiss, Cs.; Vilenius, E.; Mueller, M.; Peixinho, N.; Moreno, R.; Groussin, O.; Delsanti, A.; Harris, A. W. (September 2013). ""TNOs are Cool": A survey of the trans-Neptunian region. IX. Thermal properties of Kuiper belt objects and Centaurs from combined Herschel and Spitzer observations" (PDF). Astronomy & Astrophysics. 557: A60. arXiv:1202.3657. Bibcode:2013A&A...557A..60L. doi:10.1051/0004-6361/201322047. Retrieved 7 November 2014.
^ ^a ^b ^c Maris, Michele; Carraro, Giovanni; Parisi, M.G. (2007). "Light curves and colours of the faint Uranian irregular satellites Sycorax, Prospero, Stephano, Setebos, and Trinculo". Astronomy & Astrophysics. 472 (1): 311–319. arXiv:0704.2187. Bibcode:2007A&A...472..311M. doi:10.1051/0004-6361:20066927. S2CID 12362256.
^ ^a ^b Romon, J.; de Bergh, C.; et al. (2001). "Photometric and spectroscopic observations of Sycorax, satellite of Uranus". Astronomy & Astrophysics. 376 (1): 310–315. Bibcode:2001A&A...376..310R. doi:10.1051/0004-6361:20010934.
^ "Planetary Names § Uranian System". planetarynames.wr.usgs.gov. Archived from the original on 24 Mar 2024. Retrieved 2024-06-06.
^ ^a ^b Grav, Holman & Fraser 2004.
^ Rettig, Walsh & Consolmagno 2001.
^ Sheppard, Jewitt & Kleyna 2005.

Bibliography

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. S2CID 4315601.
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. S2CID 15706906.
Sheppard, S. S.; Jewitt, D.; Kleyna, J. (2005). "An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness". The Astronomical Journal. 129 (1): 518–525. arXiv:astro-ph/0410059. Bibcode:2005AJ....129..518S. doi:10.1086/426329. S2CID 18688556.
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.