PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
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http://www.jpl.nasa.gov

Contact:  Mary Beth Murrill                       August 13, 1996

EMBARGOED FOR RELEASE: AUGUST 13, 1996 AT 11 A.M. PDT/2 P.M. EDT

JUPITER'S EUROPA HARBORS POSSIBLE 'WARM ICE' OR LIQUID WATER 

     Tantalizing new images of Jupiter's moon Europa from NASA's 
Galileo spacecraft indicate that 'warm ice' or even liquid water 
may have existed and perhaps still exists beneath Europa's 
cracked icy crust.

     The Europa results are one of several new Galileo findings, 
including an image of a huge erupting geyser-like volcano on the 
moon Io and new information about Jupiter's Great Red Spot, 
released today at a news briefing held at NASA's Jet Propulsion 
Laboratory. 

     Galileo scientists are poring over images that show places 
on Europa resembling ice floes in Earth's polar regions, along 
with suggestions of geyser-like eruptions and details of long 
dark bands centered with white stripes that stretch like 
interstate highways across Europa's face.

     "This moon is a marvelous place," said Galileo imaging team 
scientist Dr. Ronald Greeley, a geologist at Arizona State 
University in Tempe, Ariz.  "We're seeing evidence of a lot of 
geological activity on Europa."
     
     "In some areas, the ice is broken up into large pieces that 
have shifted away from one another but that obviously fit 
together like a jigsaw puzzle," said Greeley.  "This shows the 
ice crust has been or still is lubricated from beneath by warm 
ice or maybe even liquid water."   

     The results bring scientists a step closer to discovering 
whether Europa has environmental "niches" warm and wet enough to 
meet the requirements to host life, Greeley said.

     Europa is about the size of Earth's Moon and is covered 
largely with smooth white and brownish-tinted ice instead of 
large craters like so many other bodies in the solar system.  
Scientists believe its cracked cue-ball appearance is due to 
stressing caused by the contorting tidal effects of Jupiter's 
strong gravity.  They speculate that the warmth generated by 
tidal heating may have been or may still be enough to soften or 
even liquefy some portion of Europa's icy covering.

     Europa has long been considered by scientists and celebrated 
in science fiction as one of the handful of places in the solar 
system (along with Mars and Saturn's moon Titan) that could 
possess an environment where primitive life forms could possibly 
exist.

     "A major goal of Galileo's studies of Europa is to search 
for signs of current or past activity to help answer the 
question:  Is there a liquid zone on Europa?" said Greeley.  "We 
are interested in identifying the time and places on Europa where 
liquid water might exist.  We want to go back to some of these 
areas that suggest soft ice or liquid water under the ice and 
test some of the questions we're asking now."  

     The current images, taken from more than 155,000 kilometers 
(about 95,700 miles) distance, show just 1.6 kilometer-per-pixel 
resolution, or features about one mile across.  Moon flybys later 
in the mission will bring Galileo to within 600 kilometers (370 
miles) of Europa's surface.  During those flybys, the best 
resolution from the camera will average about 22 to 30 meters per 
pixel (72 to 98 feet) and as fine as 11 meters (36 feet) per 
pixel, so that objects the size of buildings on Earth could be 
discerned, Greeley said.  

     Galileo's close Europa flybys will occur Dec. 19, 1996, Feb. 
20, 1997 and Nov. 6, 1997.  Additional non-flyby observations 
will be made this September and November and in April, June and 
September 1977.

     Galileo's images are shedding new light on the nearly 
global, highway-like stripes that scientists call "triple bands" 
because of their dark-bright-dark appearance. Originally 
discovered in data from NASA's Voyager spacecraft in 1979, the 
cracks are thought to reflect tidal stressing in Europa's icy 
crust.  "The scale of fracture patterns -- extending a distance 
equivalent to the width of the western United States -- dwarf the 
San Andreas fault in length and width," said Greeley.

     Planetary geologists have proposed several models that could 
be responsible for creating the banded roadway look of these 
features.  One set of models calls for combinations of tectonic 
faulting and flooding caused by liquid water or warm ice mixed 
with darker silicates that well up through cracks and then freeze 
over. 

     Galileo scientists say the new data suggest another model 
where 'dirty geysers' erupt along a line, ejecting a mixture of 
ice and darker silicate debris along the surface. These events 
may be followed by a more gentle, continuous flow of cleaner 
water ice that paints the white stripe down the center of the 
feature. 

     One new Galileo image of the moon Io shows a huge new blue-
colored volcanic plume extending about 100 kilometers (about 60 
miles) into space.  Scientists believe the blue color of the 
plume coming from the feature, called Ra Patera, is probably 
sulfur dioxide gas and "snow" that condenses from the gas as the 
plume expands and cools.  

     "This is very different from what we see with volcanic 
eruptions on Earth," said Galileo project scientist Dr. Torrence 
V. Johnson of JPL. "Terrestrial eruptions cannot throw materials 
to such high altitudes.  We believe that on Io we are seeing 
geyser-like eruptions that are driven by sulfur dioxide or sulfur 
gas that erupts and freezes in Io's extremely tenuous 
atmosphere."

     Galileo images have also shown that the Ra Patera plume 
glows in the dark, perhaps due to the fluorescence of sulfur and 
oxygen ions created by the breaking apart of sulfur dioxide 
molecules by energetic particles in the Jovian magnetosphere. 

     Comparing the Galileo Io images with Voyager images taken 17 
years ago, scientists have found that Ra Patera is the site of 
dramatic surface changes.  An area around the volcano of about 
40,000 square kilometers, or about the size of New Jersey, has 
been covered by new volcanic deposits since 1979.  

     Fresh Galileo images of Jupiter's Great Red Spot show new 
detail in the hurricane, which has been observed for at least 300 
years.  Winds blow counterclockwise around the Great Red Spot at 
about 400 kilometers per hour (250 miles per hour).  The size of 
the storm is more than one Earth diameter (13,000 kilometers or 
8,000 miles) in the north-south direction and more than two Earth 
diameters in the east-west direction. Galileo images are allowing 
scientists to detect varying altitudes of clouds within and 
surrounding the storm, and are showing new details in the 
structure of the giant storm.

     Galileo's next flyby of a moon of Jupiter occurs Sept. 6, 
1996, when the spacecraft will come within 250 kilometers (155 
miles) of the surface of Ganymede -- the largest
moon in the solar system.  The spacecraft accomplished its first 
encounter of Ganymede on June 27 and found remarkable tectonic 
features on the big moon.  September's flyby
of Ganymede will be about 600 kilometers (about 370 miles) closer 
than Galileo's first encounter of that moon on June 27 1996, when 
the spacecraft flew 855 kilometers (531 miles) above the surface.

     The Galileo mission is managed by the Jet Propulsion 
Laboratory for NASA's Office of Space Science, Washington, D.C.

                           #####

EDITORS NOTE:      Images to illustrate this release are 
available to media representatives by calling JPL at 818/354-
5011.  Images and other information about the Galileo mission are 
available electronically through the Galileo Internet home page 
at the following URL:  http://www.jpl.nasa.gov/galileo
     
8/13/96 MBM
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