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Sycorax (moon)

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Discovered by Philip D. Nicholson,
Brett J. Gladman,
Joseph A. Burns,
John J. Kavelaars
using the Hale telescope
Discovered in September 6, 1997
Orbital characteristics
Mean radius 12,179,000 km
Orbital eccentricity 0.5224
Orbital period 1288.28 d
Inclination 159° (to the ecliptic)[1]
Is a moon of Uranus
Physical characteristics
Mean diameter ~150 km (estimate)[1]
Surface area ~70,000 km² (estimate)
Volume ~1,800,000 km³ (estimate)
Mass ~5.4×1018 kg (estimate)
Mean density ~1.5 g/cm³ (estimate)
Surface gravity ~0.040 m/s2 (estimate)
Escape velocity ~0.087 km/s (estimate)
Rotation period  ?
Axial tilt  ?°
Albedo 0.04 (assumed)[1]
Surface temp.
min mean max
~64 K (estimate)
Atmospheric pressure 0 kPa

Sycorax is the biggest retrograde non-spherical moon of Uranus. Sycorax was found on 1997-09-06 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 designation S/1997 U 2.[2]

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


Retrograde irregular satellites of Uranus.

Sycorax follows a far orbit, more than 20 times farther from Uranus than the farthest 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.[3]

The diagram illustrates the orbital parameters of the retrograde non-spherical moons 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 albedo of 0.04)[1] making it the biggest non-spherical moon of Uranus, comparable in size with Himalia, the biggest non-spherical moon of Jupiter.

The rotation period could not be estimated well (best fit ~4 h).

Other pages


  1. 1.0 1.1 1.2 1.3 Scott S. Sheppard, David C. Jewitt, and Jan Kleyna An Ultradeep Survey for Irregular Satellites of Uranus: Limits to Completeness, The Astronomical Journal, 129 (2005), pages 518–525 . Preprint
  2. GLADMAN, NICHOLSON, BURNS, KAVELAARS, MARSDEN, WILLIAMS & OFFUTT Discovery of two distant irregular moons of Uranus, Nature, 392 (1998), pp. 897 - 899
  3. Grav, Tommy; Holman, Matthew J.; Gladman, Brett J.; Aksnes, Kaare Photometric survey of the irregular satellites,Icarus, 166,(2003), pp. 33-45. Preprint
  1. Ephemeris IAU-NSES
  2. Mean orbital parameters NASA JPL

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