Images Reveal Interesting Landscape on a Jupiter Moon - Callisto

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Aug 23, 2001

When the Galileo spacecraft performed a scheduled fly-by in May of one of Jupiter's larger moons - Callisto, it transmitted some very interesting images back to Earth that caused some excitement among many NASA scientists.

The Galileo spacecraft was originally launched to study Jupiter, but currently, it is on an extended mission to study the mammoth planet's four largest moons, especially Europa and Io. Galileo used its onboard cameras to capture the best images of Callisto as it flew 86 miles over its surface. The surface shows a spiky landscape of bright ice and dark dust with active signs of erosion.

"We haven't seen terrain like this before. It looks like erosion is still going on, which is pretty surprising," said James Klemaszewski of Academic Research Lab in Phoenix, Ariz. He is processing and analyzing the Gelileo Callisto images along with Dr. David Williams and Dr. Ronald Greeley of Arizona State University in Tempe.

The icy surface has more craters than any other body within the Solar System. With no volcanoes, winds or rain to cause the eroding, planetary scientists believe the terrain is old and caused from occasional impacts with meteorites over a long period of time.

The jagged hills in the new images may be icy material thrown outward from a large impact billions of years ago, or the highly eroded remains of a large impact structure, Williams said. Each bright peak is surrounded by darker dust that appears to be slumping off the peak.

"They are continuing to erode and will eventually disappear," Klemaszewski said. NASA scientists believe that 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. The new images show portions of the surface where the sharp knobs have apparently eroded away, leaving a plain blanketed with dark material.

Scientists are also analyzing the high-resolution images to determine how many smaller craters (about 10 feet width) are on the surface, which is a good indication of estimated the actual age of the planet.

The fly-bys by Galileo have also indicated that Callisto also has the largest saltwater ocean in the Solar System, hidden under the icy surface.