Astronomy:Sycorax (moon)

Short description: Moon of Uranus

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	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°
|{{{apsis}}}|helion}}	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)
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
Physics	~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. 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.

Retrograde 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

Animation of Sycorax's orbit around Uranus.
   Uranus  ·    Sycorax ·    Francisco  ·    Caliban  ·    Stephano  ·    Trinculo

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 common origin.

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

Full discovery image of Sycorax, located at the top-right of the image

The diameter of Sycorax is estimated at 165 km based on the thermal emission data from Spitzer and 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.

The satellite appears light-red in the visible spectrum (colour indices B–V = 0.87 V–R = 0.44, B–V = 0.78 ± 0.02 V–R = 0.62 ± 0.01, B–V = 0.839 ± 0.014 V–R = 0.531 ± 0.005), 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 about 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°.

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).

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. doi:10.1038/31890. Bibcode: 1998Natur.392..897G. 
• 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. doi:10.1086/424997. Bibcode: 2004ApJ...613L..77G. 
• 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. doi:10.1086/426329. Bibcode: 2005AJ....129..518S. 
• 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. doi:10.1006/icar.2001.6715. Bibcode: 2001Icar..154..313R. 

External links

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