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JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
Contact: Jane Platt
FOR IMMEDIATE RELEASEJuly 2, 1998
GALILEO SPACECRAFT SEES VOLCANIC FIREWORKS ON JUPITER'S MOON IO
New observations by NASA's Galileo spacecraft reveal dozens
of volcanic vents on Jupiter's fiery moon Io where lava sizzles
hotter than any surface temperatures recorded on any planetary
body in our solar system. Temperatures this high are not known
to have occurred on Earth for billions of years. At one such
volcanic vent, known as Pillan Patera, two of Galileo's
instruments have indicated the lava temperature may be 2,000
Kelvin (3,140 degrees Fahrenheit). These results are reported in
the July 3 issue of the journal Science.
"The most likely explanation for these very high
temperatures is that the eruptions contain magnesium-rich
silicates," said Dr. Alfred McEwen of the University of Arizona,
Tucson, AZ, a member of Galileo's solid state imaging camera
team. "We've tentatively identified magnesium-rich orthopyroxene
in lava flows around these hot spots. This leads us to conclude
that silicate volcanism is taking place with lava compositions
expected to melt at a very high temperature. We must now think
of Io's volcanoes in terms of the type of very high-temperature
silicate volcanism which was found on Earth during its early
days, and which we suspect occurred also on Venus and Mars."
The new findings by the Galileo camera and the spacecraft's
near infrared mapping spectrometer have updated scientists'
information on Io's volcanic processes. Previously, Io
observations made by the Voyager spacecraft in 1979 put the
highest temperature estimates at about 650 Kelvin (710 degrees
Fahrenheit). This led many scientists to believe that Io's
volcanic activity was caused by low-temperature sulfur volcanism.
In 1986, ground-based telescope observations increased the
temperature estimates to above 900 Kelvin (1,160 degrees
Fahrenheit), which suggested that silicate volcanism was
occurring at least occasionally, just as it does on Earth today.
In 1996 and 1997, Galileo identified 30 locations with
temperatures higher than 700 Kelvin (800 degrees Fahrenheit).
"This new data indicate that high-temperature eruptions on
Io are a basic and common part of its active volcanic processes,"
said Dr. Torrence Johnson of JPL, Galileo project scientist.
Johnson led the group that found the high temperature eruption in
1986. He is also a member of the near infrared mapping
spectrometer team. "Io's current volcanic activity may have a
lot in common with ancient volcanic processes on Earth and other
planets. Since the geologic record from those times is very
sparse, it's quite exciting to be able to study this type of
volcanism going on today."
"This discovery of high-temperature silicate volcanism
provides us with an extremely important clue to understanding the
geophysical processes within Io," McEwen explained. Io is heated
by periodic tides as it orbits Jupiter, along with the other
Galilean satellites (Europa, Ganymede and Callisto).
Armed with this new information, scientists also hope to
learn more about the composition of Io's crust. "Io's extreme
volcanic activity is expected to result in a low-density crust
rich in silica, sodium and potassium," said McEwen. "However,
the high-temperature volcanism suggests that the crust may be
composed of heavier lavas."
Galileo's solid state imaging camera observed Io during 11
eclipses in 5 orbits, when Io was in Jupiter's shadow, and
sunlight was blocked so the camera could better see the glowing
volcanic vents. Io's hot spots were also studied by the
spacecraft's near infrared mapping spectrometer during 11 orbits,
mostly when Io was not in eclipse. The camera provides high
spatial resolution to image the hottest features and map color
variations, while the spectrometer can observe at many
wavelengths and is sensitive to a wider temperature range. Thus,
the combination of both instruments provides a powerful means to
study Io's volcanism. The camera and spectrometer together have
discovered a total of 41 hot spots on Io.
Scientists hope to gather more detailed information about Io
with two planned close flybys in late 1999, as long as the
Galileo spacecraft remains healthy. Galileo has been orbiting
Jupiter and its four largest moons, including Io, for 2-1/2
years. It is currently in the midst of an extended journey,
known as the Galileo Europa Mission, with eight flybys of Europa
and four of Callisto, in addition to the Io flybys.
Galileo Europa Mission is managed by JPL, a division of
California Institute of Technology, Pasadena, CA.
Additional information and images taken by the Galileo
spacecraft are available on the Internet at
http://www.jpl.nasa.gov/galileo . Images are also available at