MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
Contact: Guy Webster (818) 354-6278
FOR IMMEDIATE RELEASEOctober 24, 2000
SPACECRAFT DOUBLE-TEAM THE KING OF PLANETS
Two NASA spacecraft are teaming up to scrutinize Jupiter during
the next few months to gain a better understanding of the
planet's stormy atmosphere, diverse moons, faint rings and vast
bubble of electrically charged gas.
The joint studies of the solar system's largest planet by the
Galileo and Cassini spacecraft will also resemble the passing of
a baton from the durable veteran to the promising rookie, say
mission controllers at NASA's Jet Propulsion Laboratory (JPL) in
Galileo has been running laps around Jupiter since December 1995,
continuing to produce scientific discoveries after surviving more
than double the orbital time and triple the radiation exposure
originally intended. It will pass close to Jupiter's largest
moon, Ganymede, on Dec. 28.
Cassini left Earth on Oct. 15, 1997, bound for Saturn with a
dozen scientific instruments to carry into orbit there and a
European-made probe, Huygens, to drop onto Saturn's biggest moon
in 2004. Cassini will make its closest approach to Jupiter on
Dec. 30. It will still be nearly 10 million kilometers (six
million miles) away, well outside the orbits of Jupiter's four
large moons -- Io, Europa, Callisto and Ganymede -- but within
the orbits of nine small ones.
Cassini began transmitting Jupiter pictures and data this month.
"We have a chance to make observations with a well-instrumented
spacecraft that has more capabilities than any spacecraft that
has previously visited Jupiter," said Robert Mitchell, JPL's
Cassini program manager. "Fortunately, Galileo is still operating
there, so we can get a synergistic effect in studies of Jupiter
by having spacecraft at two different locations in the vicinity
of Jupiter at the same time. That's not something we could have
counted on in 1995."
One joint study will examine how the "solar wind" of charged
particles speeding away from the Sun buffets Jupiter's
magnetosphere, the bubble of charged gas rotating around Jupiter
under the control of the planet's magnetic field. In November,
Cassini will be in the solar wind upstream of where the wind hits
the magnetosphere, while Galileo will be inside the
magnetosphere. Cassini will monitor fluctuations in the solar
wind while Galileo watches the response of Jupiter's
magnetosphere to those fluctuations.
During the past five years, Galileo has measured frequent changes
in the density of particles in the magnetosphere, but researchers
have not had the opportunity to connect the effects to specific
changes in the solar wind, said Dr. Torrence Johnson, Galileo
project scientist at JPL.
JPL physicist Dr. Scott Bolton, on science teams for both Cassini
and Galileo, said, "Having two spacecraft there at once is
possibly the only chance in our lifetime to simultaneously
connect changes in the solar wind to conditions inside Jupiter's
Getting a better grasp on how Jupiter's magnetosphere acts and
reacts will advance understanding of the smaller magnetosphere
surrounding Earth and larger ones affecting areas of the galaxy
where stars are being born, Bolton said. Disturbances in Earth's
magnetosphere can disrupt electrical and communications systems.
Another study taking advantage of dual vantagepoints will focus
on a stream of dust, finer than particles in cigarette smoke,
originating from volcanoes on Jupiter's moon Io. Patterns in the
stream as it passes first one satellite, then another, could give
information about the dust's movement. Researchers also hope to
identify its composition, which would be a sampling of material
Both spacecraft will study eclipses of Jupiter's large moons.
While the moons are in the shadow of Jupiter, glows can be seen
that are overwhelmed by reflected sunlight at other times.
Excitation of the moons' thin atmospheres by energetic particles
in Jupiter's magnetosphere causes the glows. Researchers hope to
learn more about gases on the moons by studying these glows.
Cassini will study Jupiter's atmosphere from October through
March as the craft approaches from the sunny side, then recedes
from the dark side of the planet. "If we're lucky, we may even
see a storm arise, and see how it starts and how it evolves,"
said Dr. Dennis Matson, Cassini project scientist at JPL. The
Jupiter studies will also provide a dress rehearsal, checking out
equipment and procedures for Cassini's main mission at Saturn,
JPL manages the Cassini and Galileo missions for NASA's Office of
Space Science, Washington DC. JPL is a division of the
California Institute of Technology, Pasadena. Cassini is a
cooperative endeavor of NASA, the European Space Agency and the
Italian Space Agency.
More information on the joint spacecraft study of Jupiter is
available at http://www.jpl.nasa.gov/jupiterflyby . An expanded
press kit on the study is available at http://www.jpl.nasa.gov/presskits/jupiterflyby .