JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
Contacts: Guy Webster, JPL, (818) 354-6278
Lori Stiles, University of Arizona, (520) 626-4402
FOR IMMEDIATE RELEASEOctober 26, 2000
VOLCANIC MOON IO WEARS SULFUR-RICH "SNOW" IN NEW NASA IMAGES
New pictures of the most volcanically active world in our
solar system show it also has surface activity that resembles the
accumulation and disappearance of bright snow or ice.
The images from NASA's Galileo spacecraft include the
highest-resolution view yet of Io, one of Jupiter's large moons.
A bumpy plain in that image has dark and light patches
interspersed like dark rocks reappearing through a shrinking
layer of springtime snow. Elsewhere on Io, plains appear fully
blanketed by the snow-like material.
It's not frozen water like Earth's snow, but a sulfur-rich
material that looks like white snow, said Dr. Alfred McEwen, a
planetary scientist at the University of Arizona, Tucson. In some
of Io's active volcanic plumes, the volatile material apparently
even falls to the ground as frozen particles or crystals, like
"We see this volatile material everywhere on Io where we've
had a close-up look," McEwen said. It includes sulfur dioxide and
probably other sulfur-rich substances, he said. On Earth, sulfur
dioxide is a gas. On Io, it can be either a solid or a gas at the
surface or a subsurface liquid.
The textures on Io's plains suggest that some material that had
been solid has dissipated by sublimating from a solid to a gas.
"It looks like this volatile material is sublimating or eroding
away by some means, yet it's still there," McEwen said. "We'd
like to know where it's coming from, how the surface layer is
New images also add evidence that many bowl-shaped
depressions in volcanic areas may be linked to fracturing and
shifting of Io's crust, not just to collapses above underground
magma chambers, like the large volcanic craters called calderas
The new images of Io are available online from the Jet
Propulsion Laboratory (JPL), Pasadena, Calif., at:
and from the University of Arizona Lunar and Planetary
Laboratory, Tucson, Ariz., at:
Galileo took the images during a flyby that passed within
199 kilometers (124 miles) of Io in February, and transmitted
them to Earth during the following eight months. To approach Io,
the spacecraft had to enter a region of hazardous radiation
"It's gratifying to see Galileo continuing to provide us
with new discoveries after enduring more than three times the
radiation dosage it was designed to handle," said Duane
Bindschadler, manager of Galileo's science planning and
operations team at JPL.
McEwen and other researchers have been analyzing the new images
and are describing some of their observations during meetings of
the American Astronomical Society's Division of Planetary
Sciences conference in Pasadena, Calif., this week.
Heat from many of Io's active volcanoes plays a part in
redistributing the snow-like volatiles, said University of
Arizona researcher Moses Milazzo. A bluish haze appears at edges
of lava spreading from Io's Prometheus volcano. The lava's heat
turns the volatile solids into gas, and the haze is likely
crystallization of the gas back into solid particles, like
snowflakes, above the ground, Milazzo said.
Milazzo said, "We see the bright volatiles being redeposited up
to about a kilometer away" (about a half mile away). Still,
researchers are puzzled why, over many years, the volatile stuff
has not been lost into space or become concentrated at Io's
older polar regions instead of being distributed widely across
the moon's surface.
"There's still a lot we don't understand about Io," McEwen said.
The new pictures raise questions about large depressions in Io's
surface. These features resemble some volcanic calderas on Earth,
though they are not generally found on top of mountains and their
shapes are less circular. A spectacular mosaic of pictures
covering an area with 11 of these holes suggests many are related
to cracks in Io's crust. Seven of them form a chain that makes a
right-angle bend, and the angular edges of some of the individual
depressions seem to follow the alignments of the group.
JPL, a division of the California Institute of Technology in
Pasadena, manages the Galileo mission for NASA's Office of Space
Science, Washington, D.C. The spacecraft was launched in 1989
aboard NASA's Space Shuttle Atlantis. It has been orbiting
Jupiter since late 1995.