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Harvard-Smithsonian
Center for Astrophysics Press Release
For Release: September 20,
1999
http://cfa-www.harvard.edu/cfa/ep/uranus92099.html
BUZZING LIKE A BEEHIVE: URANUS NOW
SWARMING WITH DISTANT MOONS
Until just a few years ago,
many astronomers believed the planet Uranus
was a bit strange. That's
because, unlike the other giant members of the
Solar System, Uranus did
not appear to have any so-called irregular
satellites, or, distant
moons with unusual orbits. However, recent
observations have found
what appear to be three new irregular moons
around Uranus, thus suggesting
that the seventh planet from the Sun is
just one of the gang after
all.
Using the Canada-France-Hawaii
Telescope (CFHT) on Mauna Kea, Hawaii,
an international team of
astronomers made very careful observations over
the summer to find these
extremely faint objects. If confirmed, and tallied
with two other irregular
satellites discovered in 1997, Uranus would have 16
regular and five irregular
moons, making it the most populated planetary
satellite system known.
Irregular satellites do not
follow the normal, near-circular orbits of most
satellites, such as the
Earth's Moon. Instead, these irregular objects either
travel in highly elliptical
orbits, or follow paths that are severely tipped to
the plane of the planet's
equator.
"The discovery of these irregular
satellites is very important because it
means that Uranus is not
some oddball, but rather is just like Neptune,
Saturn, and Jupiter," says
Matthew Holman, a planetary scientist at
the Harvard-Smithsonian
Center for Astrophysics and a member of the
team that made the discovery.
"It might also help us better understand
how the irregular satellites
of the giant gas planets originated and how
they've evolved."
These newly discovered objects
are being referred to as "candidate"
irregular satellites because
further observations are necessary to
absolutely confirm that
these bodies are not comets or asteroids on
planet-encountering orbits.
However, based on the data so far, the eam
is confident these are true
moons of Uranus. "Given how these bodies
are following the planet
exactly, it is highly unlikely that these are some
sort of Solar System interlopers,"
says Brett Gladman of the Observatory
of Nice, France, and
leader of the team. Gladman and his colleague J.J. Kavelaars of McMaster
University, Canada, were both members of the
team that found Uranus's
first two irregular moons in 1997.
The three new candidate satellites
were discovered in a search using the
world-class wide-field imaging
camera, known as CFH12K, which is a
mosaic of CCD detectors
covering a very large patch of sky (currently
35x28 arcmin, or roughly
the area of the full moon). This instrument
allowed the team to
explore more than 90 percent of the region around
Uranus in which satellite
orbits are stable and to find these extremely
faint objects, which are
no more than 20 kilometers in diameter and orbit
Uranus at a distance of
10 to 25 kilometers.
Other members of the discovery
team include Jean-Marc Petit and Hans
Scholl (Observatory
of Nice, France), and P. Nicholson and J. A.Burns
(Cornell University.)
Follow-up observations were obtained at the Mount
Palomar 5-meter and Kitt
Peak 4-meter telescopes, the latter in
conjunction with D. Davis
and C. Neese of the Planetary Science Institute
in Tucson, AZ. Brian Marsden
and Gareth Williams of the International
Astronomical Union's Minor
Planet Center computed preliminary orbits for
the reported objects.
Contact information:
United States:
Matthew Holman, Harvard-Smithsonian
Center for Astrophysics,
mholman@cfa.harvard.edu,
617-496-7775,
http://cfa-www.harvard.edu/~mholman
Canada:
J.J. Kavelaars, McMaster
University, kavelaars@physics.mcmaster.ca,
905-525-9140 x2716
France:
Brett Gladman, Observatory
of Nice, gladman@obs-nice.fr, 011 33 4 9200
3126, http://www.obs-nice.fr/gladman
(English and French versions)
Jean-Marc Petit, Observatory
of Nice, petit@obs-nice.fr, 011 33 4 9200
3126 Hans Scholl,
Observatory of Nice, scholl@obs-nice.fr,
011 33 4 9200 3041
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