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Closest Europa Flyby Marks Start of Galileo Mission Part II

Donald Savage
Headquarters, Washington, DC                  December 16, 1997
(Phone:  202/358-1547)

Jane Platt 
Jet Propulsion Laboratory, Pasadena, CA
(Phone:  818/354-5011)

RELEASE:  97-286

CLOSEST EUROPA FLYBY MARKS START OF GALILEO MISSION "PART II" 

     NASA's Galileo spacecraft today successfully made its 
closest-ever flyby of Jupiter's icy moon Europa, marking the 
start of an extended mission that will focus on new and 
tantalizing scientific questions raised by its just-completed, 
highly successful two-year primary mission.

     "Galileo has earned a place in history as the first 
mission to orbit an outer planet," said Dr. Wesley T. Huntress, 
Jr., NASA's associate administrator for space science, 
Washington, DC.  "Galileo already has returned a wealth of new 
information in its two-year scientific exploration of Jupiter's 
atmosphere and system of moons.  But the best yet may still be 
ahead of us as Galileo continues its mission at Jupiter with a 
focus on the moons Europa and Io in the next two years."

     Galileo dipped over Europa at an altitude of only 124 
miles (200 kilometers), with the signal received on Earth at 
7:49 a.m. EST.  This was the first encounter of the Galileo 
Europa mission, which began formally on Dec. 8, following the 
end of Galileo's primary mission.  The Galileo Europa mission 
will study Jupiter's icy satellite in detail in hopes of 
shedding more light on the intriguing prospect that liquid 
oceans may lie under Europa's ice crust. 

     New images released today from Galileo's Europa encounter 
of Nov. 6 show more evidence that the moon has been subjected 
to intense geological deformation.  The pictures show a mottled 
region of dark and splotchy terrain that scientists say 
represents some of the most recent geologic activity on Europa.  
It is believed the mottled appearance was created when chaotic 
areas of the bright, icy crust broke apart and exposed darker 
material underneath.  The new images also show a smooth, gray 
band where the Europan crust has been fractured, separated, and 
filled in with material from the interior.  Numerous isolated 
mountains or "massifs" are visible. 

     The new images represent a small portion of the 1,800 
images obtained during Galileo's primary mission, including 
hundreds of high-resolution images of Jupiter's moons.  The 
images and other information gathered by Galileo's science 
instruments have dramatically revised our knowledge of Jupiter 
and its moons, according to mission scientists.

     The Galileo Europa mission is designed to follow up on 
these discoveries and will include eight consecutive Europa 
flybys through February 1999, followed by four Callisto flybys 
and one or two Io encounters in late 1999, provided the 
spacecraft remains healthy. 

     "The Galileo Europa mission really builds upon the success 
of the prime mission which has forced us to re-think many of 
our perceptions of the Jovian system," said Galileo project 
scientist Dr. Torrence Johnson.  "We've acquired a tremendous 
pool of knowledge about Jupiter, its magnetosphere and its four 
largest moons." 

     The key findings of Galileo's primary mission include: 

*    The existence of a magnetic field on Jupiter's largest 
moon, Ganymede;
*    The discovery of volcanic ice flows and melting or 
"rafting" of ice on the surface that supports the premise of 
liquid oceans underneath at some point in Europa's history;
*    The observation of water vapor, lightning and aurora on 
Jupiter;
*    The discovery of an atmosphere of hydrogen and carbon 
dioxide on the moon Callisto;
*    The presence of metallic cores in Europa, Io and Ganymede 
and the lack of evidence of such a core in Callisto;
*    Evidence of very hot volcanic activity on Io and 
observations of dramatic changes compared to previous 
observations and even during the period of Galileo's 
observations.

     "We look forward to providing even more fascinating 
science results over the next two years," said newly appointed 
Galileo Europa mission project manager Bob Mitchell of NASA's 
Jet Propulsion Laboratory (JPL), Pasadena, CA.

     JPL manages the Galileo mission for NASA's Office of Space 
Science, Washington, DC.  The new images shown at today's 
briefing are available on the Galileo Internet home page at the 
following URL: 

              http://www.jpl.nasa.gov/galileo/ 

     Members of the Galileo mission will answer questions from 
the public during a Galileo WebChat on Wednesday, Dec. 17 from 
6 to 9 p.m. EST, at URL: http://www.jpl.nasa.gov/galileo/chat/ 

                         -end-