With regards to size, Europa pales in comparison to Jupiter.  When it comes to geological features, however, Europa is one of the most interesting objects in the solar system.  On its surface and especially beneath it lay many fascinating features.  It is believed that liquid water may be present and that tectonic activity was once at work and could possibly still be.  Leading the desire to explore Europa, though, is the idea that life may, just may, exist on this distant moon.