Galileo Millennium Mission Status 19 June 2000

NASA’s Galileo spacecraft has left the powerful influence of
Jupiter’s magnetosphere, marking the first time since early 1996
that Galileo has been outside Jupiter’s magnetic area. The
spacecraft has now entered the solar wind, which is a stream of
particles emitted continually from the Sun that flows at roughly
400 kilometers per second (about 1 million miles per hour.)

This transition from the magnetosphere to the solar wind
could be thought of as marking the beginning of the joint data
gathering by the Galileo and Cassini spacecraft. Galileo will
return close to Jupiter in October of this year, and Cassini is
preparing to swing by Jupiter in December 2000 to slingshot
toward Saturn. While both spacecraft are in Jupiter’s
neighborhood, their measurements will be compared to gain new
understanding about how the solar wind changes as it flows
outward near Jupiter’s orbit. Later this year, the simultaneous,
joint observations of the two spacecraft will allow investigators
to discover more about how the solar wind influences Jupiter’s
magnetic field and the charged particles trapped within it.

“One of the elements of study will be to try to determine
the influence of the solar wind on Jupiter’s magnetosphere,” said
Galileo Project Scientist Dr. Torrence Johnson. “We know from
previous missions that the magnetosphere is affected by the solar
wind — expanding and contracting depending on solar wind
conditions — but this will be new territory, an opportunity to
find out exactly what the solar wind is doing to the
magnetosphere.”

“We have now passed through the boundary of Jupiter’s
magnetosphere and look forward to studying its properties,” said
Dr. Margaret Kivelson, principal investigator for Galileo’s
magnetometer instrument at the Institute of Geophysics and
Planetary Physics, University of California, Los Angeles. “We
know that the boundary has two components — the shock, which is
like the sound barrier, and the magnetopause, where the direct
influence of Jupiter’s magnetic field ends. In the last week,
Galileo passed though this boundary.”

In preparation for its observations of Jupiter, Cassini
performed a flight path adjustment last week, on June 14. It is
now on the path to fly by the huge planet and will be closest to
Galileo at the end of December. This maneuver will also allow it
to pass by Saturn’s outermost moon, Phoebe, at a distance of
2,000 kilometers (about 1,250 miles). Cassini will leave the
solar wind and enter Jupiter’s magnetosphere at the end of the
year. Until then, Cassini will be analyzing cosmic dust and
continuing to make fields and particles measurements.

Additional information about the Galileo mission is
available at http://galileo.jpl.nasa.gov , and information on the
Cassini mission is at http://www.jpl.nasa.gov/cassini/ .

Galileo has been orbiting Jupiter and its moons since
December 7, 1995, and successfully completed its two-year primary
mission on December 16, 1997. That was followed by a two-year
extended mission which concluded in December 1999, and Galileo is
now continuing its studies under yet another extension, called
the Galileo Millennium Mission. JPL, a division of the California
Institute of Technology in Pasadena, manages the Galileo mission
for NASA’s Office of Space Science, Washington, D.C. Cassini is a
joint mission of NASA, the European Space Agency and Italian
Space Agency, and is managed by JPL for NASA’s Office of Space
Science, Washington, D.C.

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