Cracks and Ridges on Europa . ... What appears to be a caricature of a complex highway system on Earth is actually a system of ridges and cracks on the icy surface of Jupiter's moon Europa . The distance between parallel ridges in the above photograph is typically about 1 kilometer. The complexity of the cracks and ridges tell a story of Europa 's past that is mostly undecipherable -- planetary geologists try to understand just the general origin of the overall features. ...