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1996-01-12
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PHOTO RELEASE NO.: STScI-PRC94-50a RELEASE DATE: November 2, 1994
HUBBLE OBSERVES THE MOONS AND RINGS OF THE PLANET URANUS
This NASA Hubble Space Telescope image of the planet Uranus reveals
the planet's rings, at least five of the inner moons, and bright clouds in the
planet's southern hemisphere. Hubble now allows astronomers to revisit
the planet at a level of detail not possible since the Voyager 2 spacecraft
flew by the planet briefly, nearly a decade ago.
Hubble's new view was obtained on August 14, 1994, when Uranus was
1.7 billion miles (2.8 billion kilometers) from Earth. Similar details, as
imaged by the Wide Field Planetary Camera 2, were only previously seen
by the Voyager 2 spacecraft that flew by Uranus in 1986 (the rings were
discovered by stellar occultation experiments in 1977, but not seen directly
until Voyager flew to Uranus). Since the flyby, none of these inner
satellites has been observed further, and detailed observations of the rings
and Uranus' atmosphere have not been possible, because the rings are lost
in the planet's glare as seen through ground-based optical telescopes.
Each of the inner moons appears as a string of three dots in this picture
because it is a composite of three images, taken about six minutes apart.
When these images are combined, they show the motion of the moons
compared with the sky background. Because the moons move much more
rapidly than our own Moon, they change position noticeably over only a
few minutes. (These multiple images also help to distinguish the moons
from stars and imaging detector artifacts, i.e., cosmic rays and electronic
noise).
Thanks to Hubble's capabilities, astronomers will now be able to determine
the orbits more precisely. With this increase in accuracy, astronomers can
better probe the unusual dynamics of Uranus' complicated satellite system.
Measuring the moons' brightness in several colors might offer clues to the
satellites' origin by providing new information on their mineralogical
composition. Similar measurements of the rings should yield new insights
into their composition and origin.
One of the four gas giant planets of our solar system, Uranus is largely
featureless. HST does reveal a high altitude haze which appears as a bright
"cap" above the planet's south pole, along with clouds at southern latitudes
(similar structures were observed by Voyager). Unlike Earth, Uranus' south
pole points toward the Sun during part of the planet's 84-year orbit.
Thanks to its high resolution and ability to make observations over many
years, Hubble can follow seasonal changes in Uranus' atmosphere, which
should be unusual given the planet's large tilt.
Credit: Kenneth Seidelmann, U.S. Naval Observatory,
and NASA
These observations were conducted by a team led by Dr. Ken Seidelmann
of the U.S. Naval Observatory as Principal Investigator. These images
have been processed by Professor Douglas Currie and Mr. Dan Dowling in
the Department of Physics at the University of Maryland. Other team
members are Dr. Ben Zellner at Georgia Southern University, Dr. Dan
Pascu and Mr. Jim Rhode at the U.S. Naval Observatory, and Dr. Ed
Wells, Mr. Charles Kowal (Computer Science Corporation) and Dr. Alex
Storrs of the Space Telescope Science Institute.