A slumping cliff, migrating eruptions and churning lava
lakes appear in new images of Jupiter’s sizzling moon Io from
NASA’s Galileo spacecraft.

The images and explanatory captions are available online
at http://www.jpl.nasa.gov/images/io from NASA’s Jet
Propulsion Laboratory, Pasadena, Calif.

A high-resolution view of a cliff named Telegonus gives
information about erosion on a world that has neither surface
water nor wind. The cliff is slumping outward due to gravity.

The Tvashtar area on northern Io, where no volcanic
activity was seen prior to December 1999, now has a cluster of
hot spots. An infrared mapping image from Galileo’s Aug. 6,
2001, flyby of Io shows that the surface within the Tvashtar
area is hot at the sites observed in 1999 and 2000, as well as
at newly observed sites. “The most explosive phase of the
Tvashtar eruption may have ceased, but these observations
reveal that the area is still active,” said Dr. Rosaly Lopes,
a volcanologist at JPL. Tvashtar appears to be an example of a
volcanic site where activity starts vigorously then gradually
declines, similar to many eruptions on Earth, she said.

Io’s most powerful volcano, Loki, offers a contrasting
style of eruption. The Loki hot spot brightens and fades over
periods of several months, possibly in periodic cycles, a
pattern not known on Earth. Scientists have proposed that
Loki is either an active lava lake or a caldera whose floor is
flooded by frequent lava flows.

Infrared mapping images of Loki from Galileo’s Oct. 16,
2001, flyby of Io weigh in favor of the lava lake
interpretation. They show a concentration of high temperatures
along one edge, like a glowing shoreline. This suggests that
hotter lava from underneath is showing through where a cooler
lava crust is breaking up as it hits the crater wall. High-
resolution nighttime pictures of another of Io’s hot spots,
Pele, also show the apparent overturning of cooler crust on a
lava lake.

JPL, a division of the California Institute of Technology
in Pasadena, manages Galileo for NASA’s Office of Space
Science, Washington, D.C. For more about Galileo, visit
http://galileo.jpl.nasa.gov .