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Home :: Archive :: 1998 :: May ::
Caliban and Sycorax: Moons of Uranus
The Shakespeare Conference: SHK 9.0423  Tuesday, 5 May 1998.

From:           Mark Perew <
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Date:           Monday, 4 May 98 16:55:42 GMT
Subject:        Caliban and Sycorax: Moons of Uranus

Cornell University News Service

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FOR RELEASE: May 1, 1998

Caliban and Sycorax: Astronomers propose names for their two recently
discovered icy moons of Uranus

ITHACA, N.Y.-Cornell University astronomer Philip Nicholson and his
colleagues have proposed names for the two recently discovered moons of
the planet Uranus. They are Caliban and Sycorax, both characters in
Shakespeare's play "The Tempest." The names are likely to be approved by
the International Astronomical Union.

The astronomers detail their discovery of the two moons in a report in
the April 30 issue of the magazine Nature. They confirm that Caliban and
Sycorax are the faintest planetary moons yet imaged by ground-based
telescopes. The discovery of the two moons was reported on Oct. 31 by
Nicholson and colleagues Joseph Burns, professor of engineering and
astronomy at Cornell, Brett Gladman of the Canadian Institute for
Theoretical Physics at the University of Toronto, and J.J. Kavelaars of
McMaster University, Canada.

The team used light-sensitive semiconductors, called charge-coupled
devices, attached to the 5-meter Hale telescope on Mount Palomar,
Calif., to track the irregular, or non-circular, orbits of the two
moons. Regular satellites orbit near a planet's equatorial plane. The
two moons are the first irregular satellites discovered around Uranus.

Both Caliban and Sycorax, the astronomers write, are unusually red in
color, which suggests a link with the recently discovered populations of
comet-like bodies called trans-Neptunian objects, which orbit the sun
beyond the orbit of Neptune, and Centaurs, which cross the orbits of the
outer planets.

Both trans-Neptunians and Centaurs, say the researchers, have a wide
range of reddish colors, perhaps resulting from the bombardment of their
organic-rich icy surfaces. Nicholson says this bombardment could be from
cosmic rays or from the sun's ultraviolet radiation. The methane on the
moons' surfaces, he says, would be "cooked" by the radiation into
hydrocarbons, showing up as a dark red through a telescope's filters.

The two moons, say the researchers, are presumed to have been captured
by Uranus early in the history of the solar system. "My guess is that
the moons were once trans-Neptunians and they became Centaurs and were
captured by Uranus and became satellites," says Nicholson. Since the
newly discovered moons are likely to have been captured by Uranus soon
after its formation, the Nature article notes, "their physical
properties may provide clues to conditions in the early solar system."

The process of capture could have taken two forms, Nicholson says. The
moons could have been trapped by Uranus gravity as they came close to
the planet.  Another theory, he says, is that in the early days of the
solar system Uranus might have been surrounded by a gaseous nebula that
would have caused a drag on the objects' movement as they came close to
the planet.

Nicholson estimates that Caliban, the smaller of the two moons, has a
diameter of 60 kilometers (37 miles) and is orbiting Uranus at an
average distance of about 7.2 million kilometers (4.5 million miles),
taking 1.6 years to complete one revolution. Sycorax, he estimates, has
a diameter of 120 kilometers (74.5 miles) and takes 3.5 years to
complete one orbit of Uranus at a mean distance of about 12.2 million
kilometers (7.5 million miles) from the planet. However, he says,
Sycorax has a much more elliptical orbit than Caliban, bringing it as
close as 6 million kilometers (3.7 million miles) to the planet.

The composition of the two moons, says Nicholson, "is probably a
plum-pudding mixture of rocks and ice."

All 15 previously known satellites of Uranus lie on fairly evenly
spaced, nearly circular orbits. Most recently Voyager 2, in 1985 and
1986, discovered 10 small, dark inner moons.

Jupiter has eight known irregular satellites, of which the last, Leda,
was discovered in 1974. Saturn has one, Phoebe, discovered in 1898, and
Neptune has one, Nereid, discovered in 1949.

To see images of the two newly discovered moons of Uranus, go to
Gladman's page on the World Wide Web at
http://www.cita.utoronto.ca/~gladman/uranus.html.
 

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