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December 17, 1999
Galileo Sees Dazzling Lava Fountain on Io
During a recent close flyby of Jupiter's moon Io, NASA's Galileo spacecraft
observed a fiery lava fountain shooting more than a mile above the moon's
The images, showing a curtain of lava erupting within a giant volcanic
crater, will be unveiled today during the American Geophysical Union's fall
meeting in San Francisco. Galileo took the pictures on Thanksgiving night,
"We've finally caught a close-up of a massive volcanic eruption in action
on Io," said Galileo project scientist Dr. Torrence Johnson of NASA's Jet
Propulsion Laboratory, Pasadena, CA. "The erupting lava was so hot and
bright, it over-exposed part of the camera picture and left a bright blur
in the middle."
These lava fountains were hot enough and tall enough to be observed by the
NASA Infrared Telescope atop Mauna Kea, HI. By combining data from this
telescope and Galileo observations, scientists have their best chance ever
to pin down temperatures of the extremely hot lava on Io.
The images show a region of giant calderas, or crater depressions, in Io's
northern latitudes. They came from two of Galileo's onboard instruments --
the camera and near-infrared mapping spectrometer, which observes
wavelengths invisible to the unaided eye.
Lava fountains provide the most spectacular volcanic show on Earth,
although the fountains found in Hawaii and elsewhere on Earth rarely exceed
a few hundred yards in height. Because their appearances are infrequent
and brief, it is very difficult to target these events. "Catching these
fountains was a one-in-500-chance observation," said Galileo scientist Dr.
Alfred McEwen from the University of Arizona in Tucson.
New results from the most powerful volcano in the solar system, Loki, will
also be discussed at the press conference. These include recent
observations of Io by infrared telescopes in Hawaii and Wyoming, and two
other Galileo instruments -- the photopolarimeter radiometer and
near-infrared mapping spectrometer. These data show large changes in the
output of heat at Loki over time, with huge portions of the lava surface
appearing to be of a uniform temperature.
The telescope observations show that Loki began a period of major eruption
in early September, and Galileo caught the eruption in full force during
its October flyby of Io. While observing Loki's 120-mile (193-kilometer)
wide caldera, one Galileo instrument found a sharply defined region that
was much hotter than the rest.
"We think the hot region is the site of the eruption that began in
September," said Dr. John Spencer of Lowell Observatory, Flagstaff, AZ, a
co-investigator for the photopolarimeter radiometer, which maps surface
temperatures by measuring heat radiation. "Eventually the new lava may
spill out to cover the rest of the caldera."
The Io flybys were challenging and risky, because Io lies in an area of
intense radiation from Jupiter's radiation belts, and radiation can harm
spacecraft components. In fact, radiation-related problems garbled some of
the pictures taken by Galileo during its October 10 Io flyby. Galileo team
members thought the images were a lost cause, but engineers at JPL's
Measurement Technology Center were able to fix them with the help of
LabVIEW software from National Instruments in Austin, TX.
"It would be like watching a scrambled cable signal on television, and then
using software to unscramble the signal," Johnson said. "JPL engineers had
to break the code that was inadvertently introduced by the radiation near Io."
"They only had one-fourth of the data needed to reconstruct the images,"
said Dr. Laszlo Keszthelyi, a Galileo research associate at the University
of Arizona. "These guys found a way to intelligently guess the missing
bits. It seemed to be mathematically impossible, but they pulled it off."
The new Io images are available at http://www.jpl.nasa.gov/pictures/io .
Additional information and pictures taken by Galileo are available at
The mission is managed for NASA's Office of Space Science, Washington,
DC., by NASA's Jet Propulsion Laboratory, Pasadena, CA. JPL is a division
of the California Institute of Technology, Pasadena, CA.