Internal processes and the possible presence of liquid water beneath the ice are indicated by features such as 'dark spots', lobe- shaped flow features, 'puddles', 'mottled terrain', knobs, pits, and the darker areas along ridges and triple bands. Europa is subjected to constant tugging from the giant planet, Jupiter, as well as from its neighboring moons, Io and Ganymede. This causes 'tidal' forces that affect Europa's interior and surface. Evidence for such forces includes ridges, fractures, wedge- shaped bands, and areas of 'chaos'. Some of these features result from alternate extension and compression buckling and pulling apart Europa's icy shell.
Impact craters document external effects on a planet's surface.
Although present on Europa, impact craters are relatively scarce compared to the number seen on Ganymede, Callisto, and on the surfaces of most other 'rocky' planets and moons in our solar system. Maculae' on Europa may be the scars from large impact events. Ridges and lineaments crisscross the icy shell of Europa's surface. These are the most common landform on Europa and may represent either ejection of material from beneath its icy shell, or crumpling of the shell itself. Triple bands , seen by Voyager as linear features with a bright center and dark flanks, crisscross the surface of Europa.