A few hours before its close flyby of Io last November, Galileo flew within a few thousand kilometers of Europa and took the first really good pictures of the moon's Jupiter-facing side, which were shown at the Conference and described by Gregory Hoppa. This 12-frame mosaic provides the highest resolution view ever obtained of the side of Jupiter s moon Europa that faces the giant planet. Lower resolution context was provided by images acquired during earlier Galileo orbits. Numerous linear features in the center of the mosaic and toward the poles may have formed in response to tides strong enough to fracture Europa's icy surface. Bright white spots near the western limb are the ejecta blankets of young impact craters.
North is to the top of the picture and the sun illuminates the surface from the left.
The image, centered at 0 latitude and 10 longitude, covers an area approximately 2,500 by 3,000 kilometers. Some of the new chains run over 1600 km, with individual arcs of 50 to 400 km length. On the basis of the similar ridges already known to exist on the side of Europa facing outward from Jupiter, Hoppa and Richard Greenberg had announced last fall that the cycloids are probably cracks produced in Europa's surface ice shell by repeated cycles of stresses produced in the ice layer by Jupiter's tidal pull. The additional cycloidal ridges turning up on Europa's Jupiter-facing side provide strong further support for their theory. But the cycloids weren't their only prediction borne out by the new photos.