This Week On Galileo
October 12-18, 1998
Galileo's sole task this week is to process and transmit to Earth science images stored on the spacecraft's onboard tape recorder. The images were acquired on September 25 by the spacecraft's camera, during Galileo's 3582 kilometer (2226 mile) altitude flyby of Europa, Jupiter's icy moon.
Two camera observations are returned to Earth this week. The first is a set of images that look at a region of Europa featuring a prominent strike-slip fault zone and associated ridges and pull-apart fractures. In a strike-slip fault, the blocks of terrain on either side move relative to each other horizontally in a direction along the line of the fault, like the San Andreas fault in California. These faults and their associated features give planetary geologists clues to the stresses within Europa's crust at the time the features were formed. Ridges typically form as a result of compression (pushing together), which is typically oriented perpendicular to the long axis, or strike, of the ridge. Fractures, on the other hand, form as the result of tensional stresses (pulling apart) that crack the brittle crust. These features provide indications that Europa's surface has experienced repeated occurrences of tension and compression throughout its history.
The second observations is a single image that captures the Rhiannon crater. Rhiannon is one of only a handful of large impact craters on Europa, which have a variety of forms believed to be related to the thickness of Europa's crust in the region of the impact and/or at the time of the impacts. By comparing Rhiannon's features to those of other craters, scientists should get closer to clarifying this relationship between form and crust thickness, and closer to shedding light on any global-scale differences in crustal thickness and how the thickness has changed over geologic time.