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These views of Callisto were taken in May 2001 by the Galileo spacecraft. The top insert shows the sharp, knobby terrain experiencing erosion. As they stand now, the knobs are about 80 to 100 meters (260 to 330 feet) tall. As these knobs erode and disappear, the terrain will look more and more like the bottom insert. The smallest features discernable in these images are about 3 meters (10 feet) across.
Click on image for full size
Courtesy of NASA/JPL/Arizona State University

A Revealing Look at Callisto
News story originally written on September 5, 2001

The Galileo spacecraft was only 86 miles (138 km) above the surface of Callisto when it took the pictures to the left. These are the highest resolution views ever seen of any of Jupiter's moons. You can see features in these pictures just 10 feet (3 m) across!

The knobby landscape shown in the top insert was of most interest to scientists. Scientists thought Callisto was geologically dead, but this landscape appears to be experiencing erosion. Scientists aren't exactly sure how these hills were originally formed or why they are experiencing erosion. Scientists think the hills might have been leftover from some large impact billions of years ago. Whatever the cause of their formation, each icy hill is now surrounded by darker dust that appears to be slumping off the peak. "One theory for an erosion process is that, as some of the ice sublimes away into vapor, it leaves behind dust that was bound in the ice. The accumulating dark material may also absorb enough heat from the Sun to warm the ice adjacent to it and keep the process going." (Text courtesy of JPL News) The hills will eventually disappear as erosion continues. The lower insert shows a portion of the surface where the hills have more completely eroded away, leaving a plain of dark material.

Callisto is one of the Jupiter's Galilean moons. Callisto is an icy moon about the same size as Mercury.

Last modified September 4, 2001 by Jennifer Bergman.

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