MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011

Contact: Jane Platt (818) 354-0880

FOR IMMEDIATE RELEASE February 18, 2000

NASA’s Galileo spacecraft is trying to go “three for three” as it attempts its third and closest flyby of
Jupiter’s fiery moon Io, the most volcanic body in the solar system.

The spacecraft will dip to only 200 kilometers (124 miles) above Io’s surface — roughly the distance
between Los Angeles and San Diego — at 6:32 a.m. Pacific Standard Time on Tuesday, February 22.
Galileo gathered a wealth of pictures and other scientific information during its flybys of Io in October and
November of 1999.

“Io’s volcanoes are so active that the moon’s surface is always changing, and with each flyby we get
new and different observations,” said Dr. Torrence Johnson, Galileo project scientist at NASA’s Jet
Propulsion Laboratory. “This time we expect to be able to observe the effects of the eruptions we saw in
the October and November Io flybys.”

The Io flybys represent a classic case of “no pain, no gain,” since Io orbits close to Jupiter in a region
bombarded by radiation from the huge planet’s radiation belts. That radiation can disrupt spacecraft systems
or even knock out instruments, but mission planners believe potential gains in scientific knowledge outweigh
the risks of the Io flybys. Nonetheless, the encounters were planned near the end of Galileo’s extended
missions, when the spacecraft has already returned volumes of pictures and information from Jupiter and its
moons.

“Although we gathered some great images and data during the previous Io flybys, the radiation did
cause some problems, and we won’t be surprised if that happens again this time,” said Galileo Project
Manager Jim Erickson of JPL. “Galileo has already survived more than twice the radiation it was designed
to withstand, so we’re keeping our fingers crossed that it will complete this encounter with flying colors.”

Galileo engineers often say that the spacecraft has “lived well past its warranty.” Galileo entered orbit
around Jupiter in December 1995. It was originally assigned to spend two years studying Jupiter, its moons
and its magnetic environment. When that original mission ended in December 1997, it was followed by a
two-year extended mission, which ended in January 2000. This Io flyby is part of an additional extension,
called the Galileo Millennium Mission.

Additional information about the Galileo mission is available at
http://galileo.jpl.nasa.gov.

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.

#####

2/17/00 JP
#2000-018