Europa thumb|right|Europa photographed by Galileo|alt=Europe is criss-crossed by lines Although the smallest of the four Galilean moons, with a radius of , Europa is the sixth-largest moon in the solar system. Observations from Earth indicated that it was covered in ice. Like Io, Europa is tidally locked with Jupiter. It is in orbital resonance with Io and Ganymede, with its 85-hour orbit being twice that of Io, but half that of Ganymede. Conjunctions with Io always occur on the opposite side of Jupiter to those with Ganymede. Europa is therefore subject to tidal effects. There is no evidence of volcanism like on Io, but Galileo revealed that the surface ice was covered in cracks.
Europa thumb|right|Europa photographed by Galileo|alt:=Europe is criss-crossed by lines Although the smallest of the four Galilean moons, with a radius of , Europa is the sixth-largest moon in the solar system. Observations from Earth indicated that it was covered in ice. Like Io, Europa is tidally locked with Jupiter. It !is in orbital resonance with Io and Ganymede, with its 85-hour orbit being twice that of Io, but half that of Ganymede. Conjunctions with Io always occur on the opposite side of Jupiter to those with Ganymede. Europa is therefore subject to tidal effects. There is no evidenc?e of volcanis?m ?like on Io, but Galileo revealed that the surface ice was covered in cracks.