The press release regarding the Europa imaging results...

SAR Moderator
+++++

Douglas Isbell
Headquarters, Washington, DC          August 13, 1996 (Phone:  202/358-1753)

Mary Beth Murrill
Jet Propulsion Laboratory, Pasadena, CA 
(Phone: 818/354-5011)

RELEASE:  96-164

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 today 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 Jupiter's moon Io and new
information about Jupiter's Great Red Spot, released today in a news briefing
at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.

        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 Dr. Ronald Greeley, a Galileo
imaging team scientist and a geologist at Arizona State University, Tempe,
AZ.  "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 obviously fit together like a jigsaw
puzzle," said Greeley.  "This shows the ice crust has been or still is
lubricated from below by warm ice or maybe even liquid water."   

        The results bring scientists a step closer to determining whether
Europa has environmental "niches" warm enough 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 sufficient 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 forms of life 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 a distance of about 95,700 miles
(155,000 kilometers), show features about one mile across (1.6 kilometer per
pixel resolution).  Moon flybys later in the mission will bring the Galileo
spacecraft to within 370 miles (600 kilometers) of Europa's surface.  During
those flybys, the best resolution from the camera will average about 72 to 98
feet (22 to 30 meters- per-pixel) and as fine as 36 feet (11 meters) per
pixel, so that objects the size of buildings on Earth could be discerned,
Greeley said.   

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

        Galileo's detailed images are shedding new light on the nearly global,
highway-like stripes on Europa 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.  This event may be followed by a more
gentle, continuous flow of cleaner water ice that paints the white stripe
down the center of the feature. 

        In other mission results, one new Galileo image of the moon Io shows
a huge new blue-colored volcanic plume extending about 60 miles (about 100
kilometers) into space.  Scientists believe the blue color of the plume coming
from the feature, called Ra Patera, is probably due to tiny particles of
sulfur dioxide "snow" that condense 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 about the size of the state of New Jersey
(about 40,000 square kilometers) 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 250 miles per hour (400
kilometers per hour).  The size of the storm is more than one Earth diameter
(8,000 miles or 13,000 kilometers) 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 155 miles (250 kilometers) 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 370
miles (about 600 kilometers) closer than Galileo's first encounter of that
moon in the previous flyby, when the spacecraft flew 531 miles (855
kilometers) above the surface.

      The Galileo mission is managed by JPL for NASA's Office of Space
Science, Washington, DC.

EDITOR'S NOTE:  Images to illustrate this release are available to media
representatives by calling JPL at 818/354-5011.  Images released today, and
other information about the Galileo mission, will be available electronically
through the Galileo Internet home page at the following URL: 

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

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