Images Reveal Callisto as Jagged and Bleak

Aug. 23 -- It's jagged with bright peaks of ice and it's full of holes.

High-resolution pictures taken of Jupiter's moon, Callisto, reveal a place that has likely not seen any geological activity such as volcanoes or tectonic shifting for millions of years. The images, snapped a few months ago by NASA's Galileo spacecraft about 86 miles above Callisto's surface, are the best yet taken of any of Jupiter's moons.

"We haven't seen terrain like this before," James Klemaszewski of Academic Research Lab in Phoenix, Ariz., said in a NASA release. "It looks like erosion is still going on, which is pretty surprising."

Several impact craters pockmark the ice and rock surface of the most distant of Jupiter's four large moons. The fact that no volcanoes or earthquakes have erased the craters suggests the moon has long been a very still planet.

Vaporizing Ice Peaks

The surface also features jagged peaks of what scientists believe is dust-filled ice. One theory is the icy material splashed outward from a powerful impact billions of years ago. NASA scientists report each bright peak is surrounded by rings of dark dust that appear to be eroding off the peak.

"They are continuing to erode and will eventually disappear," said Klemaszewski about the peaks.

Klemaszewski and his colleagues, David Williams and Ronald Greeley of Arizona State University suggest the dark dust rings are formed as the ice peaks turn into vapor. Dust that had been bound in the ice is then left behind. The dust rings could then attract sunlight which would heat the ice and continue the vaporization process.

Counting Craters

Close-up images of the craters reveal the smallest measure about 10 feet across. The NASA team hopes to count the number of small craters on the moon since this is one way to estimate the age of a moon's surface.

And because Callisto is considered to be a very inactive moon, crater estimates of its surface could then be useful in gauging the age of Jupiter's other moons.