2.3 Examining Europa's surface
It is all very well speculating about conditions in an ocean below Europa's ice, but what evidence is there that it actually exists? After all, tidal heating might not result in ice melting on a global scale, and current geophysical models of Europa's internal structure (e.g. Figure 14 in Section 1.5) cannot tell the difference between ice and liquid water. Fortunately, Voyager and Galileo have given us detailed images of Europa that we can use in the same way that a geologist uses aerial photographs or images from space to help decipher the processes that have shaped a particular tract of the Earth's surface.