Caliban (pronounced /ˈkælɨbæn/ KAL-i-ban, or /ˈkælɨbən/ KAL-ə-bən) is the second largest retrograde irregular moon of Uranus. It 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 Sycorax and given the temporary designation S/1997 U 1.
Designated Uranus XVI it was named after the monster character in William Shakespeare's play The Tempest.
Caliban follows a distant orbit, more than 10 times further from Uranus than the furthest regular moon Oberon. Its orbit is retrograde, moderately inclined and slightly eccentric. The orbital parameters suggest that it may belong, together with Stephano and Francisco 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.
Its diameter is estimated at 72 km (assuming albedo of 0.04) making it the second largest irregular satellite of Uranus, half the size of Sycorax, the biggest irregular satellite of Uranus.
Somewhat inconsistent reports put Caliban in light-red category (B–V = 0.83 V–R = 0.52, B–V = 0.84 ± 0.03 V–R = 0.57 ± 0.03), redder than Himalia but still less red than most Kuiper Belt objects. Caliban may be slightly redder than Sycorax. It also absorbs light at 0.7 um, and one group of astronomers think this may be a result of liquid water that modified the surface.
The light curve suggests the rotation period of Caliban is about 2.7h.
Caliban 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' mass (so called, pull-down).
* Moons of Uranus
1. ^ a b c Gladman, Brett J.; Nicholson, Philip D.; Burns, Joseph A. et al. (1998). "Discovery of two distant irregular moons of Uranus". Nature 392: 897–899. doi:10.1038/31890.
* Caliban Profile by NASA's Solar System Exploration
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