Smoothest Body Around
Europa, pictured in the image to the right,
may be the smoothest solid body in the Solar System. It
appears to be covered with a frozen water ocean and has very few craters.
As the adjacent image indicates, it is covered with cracks, but these seem
to have little vertical relief (Ref).
Details of the crazed cracks criss-crossing Europa's frozen surface are apparent in this mosaic of the Galileo spacecraft's latest images of Jupiter's ice-covered moon shown to the left (Ref). Here is a further discussion of these Cracked Ice Plains of Europa.
History of Europa
Europa, like Io, is heated internally by the tidal tug-of-war with Jupiter, but because Europa is further from Jupiter than Io the tidal effect is less dramatic. In the case of Europa, the effect of the tides induced by Jupiter is to heat the interior of Europa sufficiently to keep the surface soft. Thus, no vertical relief features can survive for long on Europa's surface, explaining its smooth appearance.
Information supplied by: http://csep10.phys.utk.edu