Plains and Ridges on Europa . ... Credit Copyright: Galileo Project , JPL , NASA Explanation: The ridges on Europa may be caused by cold water volcanoes. Europa , one of the largest moons of Jupiter , has been the source of intense scrutiny since speculation increased of there being oceans beneath its icy surface . ... The above image highlights features common to Europa's surface : pure blue water ice beneath lighter ridges that run for many kilometers. ... NASA Official: Jay Norris. ...