Europa
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- Europa displayed a large number
of intersecting linear features in the distant, low-resolution photos from Voyager 1.
Scientists at first believed the features might be deep cracks, caused by crustal rifting
or tectonic processes. Closer, high- resolution photos by Voyager 2, however, left
scientists puzzled: The features were so lacking in topographic relief that they
"might have been painted on with a felt marker," one scientist commented. There
is a possibility that Europa may be internally active due to tidal heating at a level
one-tenth or less that of Io. Models of Europa's interior show that beneath a thin crust
(5 kilometers or 3 miles) of water ice, Europa may have oceans as deep as 50 kilometers
(30 miles) or more.
