The sharpest images ever taken of Jupiter's icy moon Callisto show features never seen before on the remote body–icy, knoblike spires that show slow but steady signs of erosion. That's a puzzle because other evidence indicates that Callisto, the most distant of Jupiter's four largest moons, has been inactive for billions of years.
The Galileo spacecraft recorded the spires, which are 80 to 100 meters high, when it passed just 138 kilometers above the moon last May. The images, unveiled Aug. 22, provide the highest-resolution view of any of Jupiter's moons, showing features as small as 3 m across.
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