Galileo Sees Dazzling Lava Fountain on Io

Douglas Isbell

Headquarters, Washington, DC

(Phone: 202/358-1753)

Jane Platt

Jet Propulsion Laboratory, Pasadena, CA

(Phone: 818/354-5011)

RELEASE: 99-148

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 surface.

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, November 25.

“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.”