Press Release

Cassini Visualizes the Invisible, Tracks Giant Storms

By SpaceRef Editor
December 30, 2000
Filed under ,

NASA’s Cassini spacecraft, which made its closest
approach to Jupiter early today, is providing ways to make
invisible features visible, to track daily changes in some of
the planet’s most visible storms, and to hear the patterns in
natural radio emissions near the edge of Jupiter’s magnetic
environment.

In collaboration with NASA’s Galileo spacecraft, which
has been orbiting Jupiter since 1995, Cassini is also
beginning to provide new insight in how the solar wind of
particles speeding away from the Sun affects a huge magnetic
region surrounding Jupiter.

Scientists using instruments on both Cassini and Galileo
gave a preview today at NASA’s Jet Propulsion Laboratory,
Pasadena, Calif., of what they are beginning to learn in the
joint studies, which will continue for another three months.

Large storms on Jupiter, which can be larger than Earth
and last for centuries, gain energy from swallowing smaller
storms, preliminary analysis of Jupiter movies from Cassini
spacecraft suggest. The smaller storms pull their energy from
lower depths, according to information collected by Galileo.

The Cassini spacecraft, which made its closest approach
to Jupiter today at 2:12 a.m. Pacific Standard Time, has taken
pictures of thunderstorms on Jupiter. As small storms pass
each other, they can be ripped apart, or merged together. This
shows that the small features in Jupiter’s atmosphere harvest
the energy from below the cloud surface, and the larger storms
encompass the small ones, just as a big fish eats smaller ones
for energy, said Dr. Andrew Ingersoll of the California
Institute of Technology.

He said a better understanding of storms on Jupiter helps
in understanding Earth’s atmosphere, too. “The weather is
different on Jupiter. You have a 300-year-old storm. We’d like
to know why Jupiter’s weather is so stable, and Earth’s is so
transient,” he said.

Dr. Carolyn Porco of the University of Arizona presented
planetwide movies of cloud movements on Jupiter, a sampling of
the Cassini camera results that scientists will be examining
in coming months.

“The camera has performed beyond our wildest imaginings –
– and that’s saying something, because we’ve been imagining
this for a decade now,” she said.

Both Cassini and Galileo have recently returned evidence
of the variability in size of Jupiter’s magnetosphere, a
bubble of charged particles trapped within Jupiter’s magnetic
field. The bubble is so big that if it were visible to the
eye, it would appear bigger to viewers on Earth than our own
Moon does, despite its much greater distance. While Galileo
was moving toward Jupiter this fall, it passed the
magnetosphere boundary, but then the boundary moved inward
toward Jupiter even faster than the spacecraft was moving,
temporarily putting Galileo back outside the magnetosphere,
said Dr. William Kurth of the University of Iowa.

Kurth played a sound recording based on natural radio
emissions created by the energy of the area where the solar
wind hits Jupiter’s magnetosphere. The emissions were detected
on an instrument onboard Cassini, which encountered the
boundary this week much farther out from Jupiter than
expected.

Another instument on Cassini is creating images never
before possible of the entire magnetosphere. Dr. Stamatios
(Tom) Krimigis of Johns Hopkins University’s Applied Physics
Laboratory presented one at the briefing that Cassini took
this week, showing some features of the structure within the
magnetosphere. Other Cassini measurements show that some
sulfur and oxygen spewed from volcanoes on Jupiter’s moon Io
are distributed much farther from the planet than the extent
of the magnetosphere, Krimigis said.

The evidence shows there is big nebula of material
surrounding Jupiter, originating from the volcanoes on Io, he
said.

Cassini passed about 9.7 million kilometers (6 million
miles) from Jupiter today in order to use Jupiter’s gravity
for a boost to take Cassini to its main destination, Saturn.
It will reach Saturn in 2004.

The images and sounds released at the briefing are
available online from JPL at
http://www.jpl.nasa.gov .

Cassini is a cooperative effort of NASA, the European
Space Agency and the Italian Space Agency. JPL, a division of
the California Institute of Technology in Pasadena, manages
Galileo and Cassini for the NASA Office of Space Science,
Washington, D.C.

SpaceRef staff editor.