Building Ridges

Ridges appear in nearly every images of Europa's surface. In Chapter 2 we saw beautiful examples of simple double ridges, of global-scale complexes of multiple entwined ridges, and of terrain packed densely with criss-crossing ridges. Even within chaotic terrain, the rafts often display portions of earlier, ridged terrain that predated the chaos. We saw that the common denominator of ridges, in all their diversity, is the double ridge. Of the thousands of European ridges that I have surveyed, my favourite is shown in the spectular high-resolution view in Fig.7.1.

This view is so close-up that bumps as small as a house are visible. The view is at an angle, like looking sideways out the window of an airplane. A double ridge, curving down from top-center, rides over other ridges coming from the upper left. The double ridge is sliced off, revealing its interior, just as a roadcut created during highway construction reveals its interior, just as a roadcut created during highway construction reveals the layers of different materials below the surface. The terrain in the foreground is probably chaos, and most likely it was during its formation that the ridges were cut off and the interiors were revealed. What makes this image so special is not only that the view is amazingly close-up, but that it allows us to look inside the ridges.

Another reason I like this picture so much is that it was hidden away for a time, until my student Greg Hoppa dug it up and started showing it around. Even members of the imaging team were surprised that it existed. Naturally, I like to call it The Picture the US Government Did Not Want You to See.