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Contact: Guy Webster, JPL, (818) 354-6278
Jim Scott, University of Colorado, (303) 492-3114
FOR IMMEDIATE RELEASEJanuary 24, 2001, 2001
CASSINI 'SEES' INVISIBLE GAS DOUGHNUT AROUND JUPITER
NASA's Cassini spacecraft is helping scientists see the
structure and hour-to-hour changes of a giant doughnut-shaped
gaseous ring around Jupiter in unprecedented detail.
The doughnut, called the Io torus, draws its raw material
from gases spewed into space by volcanoes on Io, one of Jupiter's
The torus was detected in the 1970s, but almost all of its
light is invisible to the human eye. It is big enough that if
Earth were in the middle, the orbit of Earth's Moon would fit
inside the hole of the doughnut.
The first movie clip of the gyrating Io torus in extreme
ultraviolet light is available online from NASA's Jet Propulsion
Laboratory, Pasadena, Calif., at
"We're visualizing the torus and seeing it evolve and change
in a level of detail that people haven't seen before," said
Dr. Larry Esposito, a planetary scientist at the University
of Colorado, Boulder, and principal investigator for Cassini's ultraviolet imaging spectrograph instrument.
He and University of Colorado's Ian Stewart and other colleagues
are examining what the ultraviolet information can add to
understanding about the composition and temperature of the torus
and the processes that produce it.
The source of specific wavelengths of ultraviolet glow coming
from the torus can be identified as positively charged ions of
oxygen and sulfur, Esposito said.
Cassini, built, operated and managed by JPL, is monitoring the
concentrations, temperatures and distribution of the ions over a
six-month period to check and build upon current explanations for
the torus. Gases from Io's volcanoes contain oxygen and sulfur.
The torus apparently gets its ingredients and shape when some of
the neutral oxygen and sulfur atoms around Io become ionized by
exposure to radiation from the Sun or from a radiation belt that
surrounds Jupiter. As ions, they are stuck to lines of magnetic
force in Jupiter's strong magnetic field. That field twirls along
with the planet's rotation, dragging the ions in circular paths
around Jupiter, so a shape that begins as a sphere around Io
becomes a torus around Jupiter.
The ultraviolet instrument on Cassini has checked the Io torus
almost daily since Oct. 1, 2000. So far, the monitoring shows a
gradual decline in overall brightness. The torus material
apparently dissipates and cools over time, to be replenished and
re-energized by the next episode of volcanic activity from Io.
"We might be seeing the tail end of one of those episodes,"
Esposito said. "We're hoping Io will give us a new injection of
material so we can track the effects."
Cassini passed its closest to Jupiter on Dec. 30, gaining a
gravitational boost needed for reaching its main destination,
Saturn. It will continue studying the environment around Jupiter
until March 22.
Esposito said he looks forward to investigating clues of a
related phenomenon at Saturn involving gases from the dense
atmosphere of Saturn's largest moon, Titan. Cassini will reach
Saturn in July 2004. Information about the dynamics of the Io
torus and its possible cousin at Saturn could deepen
understanding of other phenomena linked to magnetic fields, said
Espositio. These phenomena include powerful magnetic storms that
can disrupt communications on Earth, and the shaping of nascent
solar systems called planetary accretion discs that can exist
within the magnetic-field influence of newly forming stars.
Cassini is a cooperative mission of NASA, the European Space
Agency and the Italian Space Agency. JPL, a division of the
California Institute of Technology in Pasadena, manages Cassini
for NASA's Office of Space Science, Washington, D.C. Further
information about the mission is available at
[NOTE TO BROADCASTERS: A video file with animation to accompany
this release will air Jan. 25 on NASA Television at noon, 3 p.m.,
6 p.m. and 9 p.m. Eastern Standard Time. Opportunities for live
interviews from JPL with Dr. Esposito are available Jan. 26
between 4:30 p.m and 8 p.m. Eastern Standard Time. To arrange an
interview time, contact Jack Dawson at 818-354-0040. NASA
Television is broadcast on GE-2, transponder 9C, C-Band, located
at 85 degrees West longitude. The frequency is 3880.0 MHz.
Polarization is vertical and audio is monaural at 6.8 MHz. For
general questions about the NASA Video File, contact: Fred Brown,
NASA Television, Washington, D.C. (202) 358- 0713.]