The United States sent two spacecraft, Pioneer 10 and 11, to Jupiter in the early 1970's. No one knew if a spacecraft could survive a flyby of Jupiter, but the Pioneers did survive, and they sent back valuable information for the next space mission. However, the Pioneer photographs of Jupiter's largest moons were fuzzy and dim. The twin Voyager spacecraft flew by Jupiter and its moons in 1979, giving us our first close-up view of Europa. Voyager pictures show pale-yellow icy plains with red and brown mottled regions.
Long cracks run for thousands of kilometers over the surface.
On Earth, these cracks would indicate such features as tall mountains and deep canyons. But none of these features are higher than a few kilometers on Europa, making it one of the smoothest objects in our Solar System. If we look at the surface more closely, as we have with the instruments on the Galileo spacecraft, we see some fascinating features. Europa looks like broken glass that is repaired by an icy glue oozing up from below. Low ridges, straight and curved, crisscross the surface.