Sycorax is the largest irregular satellite of

Uranus Uranus is the seventh planet from the Sun. It is a gaseous cyan-coloured ice giant. Most of the planet is made of water, ammonia, and methane in a Supercritical fluid, supercritical phase of matter, which astronomy calls "ice" or Volatile ( ...

. It was discovered in September, 1997 on the

Hale Telescope The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in San Diego County, California, US, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation in 1928, he orchestrated the planning, de ...

in California. Sycorax's orbit is retrograde, irregular, and much more distant than that of Oberon, the furthest of Uranus's regular moons. With a diameter of over , it is the largest irregular moon of Uranus. It has been hypothesized 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 Joseph Burns (March 22, 1941February 26, 2025) was a professor at Cornell University with a dual appointment in the Sibley School of Mechanical and Aerospace Engineering (MAE) and the Astronomy department. His primary area of research was dynamics ...

, and John J. Kavelaars using the 200-inch

, together with Caliban. At the time, it was given the temporary designation S/1997 U 2. Officially confirmed as Uranus XVII, it was named after

Sycorax Sycorax is an unseen character in William Shakespeare's play ''The Tempest'' (1611). She is a vicious and powerful witch and the mother of Caliban (character), Caliban, one of the few native inhabitants of the island on which Prospero, the he ...

, Caliban's mother in

William Shakespeare William Shakespeare ( 23 April 1564 – 23 April 1616) was an English playwright, poet and actor. He is widely regarded as the greatest writer in the English language and the world's pre-eminent dramatist. He is often called England's nation ...

's play ''

The Tempest ''The Tempest'' is a Shakespeare's plays, play by William Shakespeare, probably written in 1610–1611, and thought to be one of the last plays that he wrote alone. After the first scene, which takes place on a ship at sea during a tempest, th ...

''. This follows the trend that all Uranian moons are named after Shakespearean characters or those from Alexander Pope's '' The Rape of the Lock''.

Orbit

Sycorax follows a distant orbit, more than 20 times further from Uranus than the furthest regular moon,

Oberon Oberon () is a king of the fairy, fairies in Middle Ages, medieval and Renaissance literature. He is best known as a character in William Shakespeare's play ''A Midsummer Night's Dream'', in which he is King of the Fairies and spouse of Titania ...

. Its orbit is retrograde, moderately inclined and eccentric. The orbital parameters suggest that it may belong, together with Setebos and

Prospero Prospero ( ) is a fictional character and the protagonist of William Shakespeare's ''The Tempest''. Character Twelve years before the play begins, Prospero is usurped from his position as the rightful Duke of Milan by his brother Antonio, ...

, 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 An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

to the apocentre.

Physical characteristics

The diameter of Sycorax is estimated at , 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 The visible spectrum is the spectral band, band of the electromagnetic spectrum that is visual perception, visible to the human eye. Electromagnetic radiation in this range of wavelengths is called ''visible light'' (or simply light). The optica ...

( colour indices , , ), redder than Himalia but still less red than most

Kuiper belt The Kuiper belt ( ) is a circumstellar disc in the outer Solar System, extending from the orbit of Neptune at 30 astronomical units (AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt, but is far larger—20 times ...

objects. However, in the

near infrared Infrared (IR; sometimes called infrared light) is electromagnetic radiation (EMR) with wavelengths longer than that of visible light but shorter than microwaves. The infrared spectral band begins with the waves that are just longer than those o ...

, 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 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 In astronomy, a light curve is a graph (discrete mathematics), graph of the Radiance, light intensity of a celestial object or region as a function of time, typically with the magnitude (astronomy), magnitude of light received on the ''y''-axis ...

suggest it is being viewed at a near equator-on configuration. In this case, Sycorax may have a north pole

right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the equinox (celestial coordinates), March equinox to the (hour circle of the) point in questio ...

around 356° and a north pole

declination In astronomy, declination (abbreviated dec; symbol ''δ'') is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. The declination angle is measured north (positive) or ...

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 In thermodynamics, dissipation is the result of an irreversible process that affects a thermodynamic system. In a dissipative process, energy ( internal, bulk flow kinetic, or system potential) transforms from an initial form to a final form, wh ...

of energy. Possible capture processes include gas drag in the

protoplanetary disk A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may not be considered an accretion disk; while the two are sim ...

and many-body interactions and capture during the fast growth of Uranus's mass (so-called ''pull-down'').

References

Bibliography

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External links

Sycorax Profile
(b
NASA's Solar System Exploration

(by Scott S. Sheppard)
MPC: Natural Satellites Ephemeris Service
{{DEFAULTSORT:Sycorax (Moon) Moons of Uranus Irregular satellites 19970906 Moons with a retrograde orbit Discoveries by Brett J. Gladman The Tempest