are abundant on Jupiter's moon Io
NASA/Jet Propulsion Laboratory
Abundant volcanoes, including
some that turn on and off, and puzzling surface textures are some
of the new findings from NASA's Galileo spacecraft during the closest flyby ever of Jupiter's
An active volcanic eruption on Jupiter's moon
Io was captured in this image taken on February 22, 2000 by
NASA's Galileo spacecraft
Images and other data
gathered by Galileo during a flyby of Io on February 22 will be
released today at the American Geophysical Union's spring meeting
in Washington, D.C.
observations made by one of the instruments on Galileo, the near-infrared
mapping spectrometer, revealed 14 volcanoes in a region that was
previously known to have only four. The region covers about five
percent of Io's surface and is about three times larger than Texas.
Before the flybys, Io was known to have only about 81 active volcanoes.
"Since the distribution
of active volcanoes on Io appears to be uniform, we can expect Io
to have some 300 active volcanoes, most of which have not been discovered," said Dr.
Rosaly Lopes- Gautier, research scientist at NASA's Jet
Propulsion Laboratory, Pasadena, Calif.
Detail of one of the calderas, or collapsed volcanic
craters, on Jupiter's moon Io, is seen in these images acquired
on February 22, 2000 by NASA's Galileo spacecraft. Taken from
a distance of 700 to 800 kilometers (roughly 400 to 500 miles).
The five partial images on the right comprise all of the data
that could be returned from an eight-image mosaic.
Scientists have detected
changes in the months between the three different flybys in October
1999, November 1999 and February 2000. Some of the smaller, fainter volcanoes appear to
turn on and off, changing from hot and glowing to cool and dim within
a few weeks. The larger or brighter volcanoes tend to remain active
for years or even decades, based on previous observations by Galileo
and the Voyager spacecraft that flew through the Jovian system in
Loki, the most powerful
volcano in the solar system, was scanned by Galileo's photopolarimeter/radiometer
during the October 1999 flyby and again this past February. These two close-
up views showed Loki near the beginning and end of one of its periodic
This image shows one of many intriguing mountains on Jupiter's moon Io. The image was made by combining a recent high- resolution, black and white image with earlier low-resolution color data to provide a high-resolution, color view.
"Most of the surface
of its caldera, a region of more than 10,000 square kilometers (about
4,000 square miles) or half the size of Massachusetts, seems to
have been covered by hot lava in the intervening four and a half
months," said Dr. John Spencer of Lowell Observatory, Flagstaff,
Ariz., co- investigator for the radiometer instrument.
New images show that
Chaac Patera has a caldera wall that is about 2.8 kilometers (1.7
miles) high with a 70-degree slope -- about twice as high and steep
as the typical slopes of the Grand Canyon.
"The wall rocks
must be very strong to support this topography," said Dr. Alfred
S. McEwen of the University of Arizona, Tucson, a member of the
Galileo imaging team. "Each volcanic center on Io is proving
to have unique characteristics."
Observations also show
a smaller caldera filled with bright white deposits containing sulfur
dioxide that is purer than at any other place observed on Io. Scientists
believe it may be a frozen layer of sulfur dioxide ice.
One of the most spectacular
volcanic eruptions observed by Galileo was from Tvashtar Catena
in November 1999. The February images show that the eruption seen in November has waned,
but there is a new eruption with extremely hot lava
The February Io flyby
has yielded more images with higher resolution than previous flybys.
They show unprecedented views of small surface areas that give new clues about the volcanic
terrain but also reveal landforms that are perplexing to geologists.
There are views of one surface area that appears eroded, showing
thin, alternating bright and dark layers. Scientists don't yet understand
how the layers formed and were eroded or how other plains textures
on Io have formed.
"There are processes
on Io for which we have no terrestrial experience," said McEwen.
"Strange new observations like these will provide fodder to current and future scientists for understanding
the processes that have shaped this fascinating world."