They could be frozen remnants of cryovolcanic activity which occured when water or partly molten water ice erupted on the Europan surface, freezing almost instantly in the extremely low temperatures so far from our sun. Dark spots, several kilometers in diameter, are distributed over the surface. A geologically older, smoother surface, bluish in tone, underlies the ridge system. The blue surface is composed of almost pure water ice, whereas the composition of the dark, brownish spots and ridges is not certain. One possibility is that they contain evaporites such as mineral salts in a matrix of high water content.
North is to the lower left of the picture and the sun illuminates the surface from the upper left.
The colors have been enhanced to bring out the details. An astronaut orbiting this smallest of the four Galilean satellites would see the icy surface of Europa somewhat brighter, but with less intense colors. Combining the lower resolution and high resolution images enables scientists to investigate both the surface features in great detail as well as the color or compositional information in a regional context. The ASU Planetary Geology Group is under the direction of Dr. Ronald Greeley.