Jupiter has four main moons, which were discovered by Galileo, as well as many smaller ones (47 Jovian moons are currently known). Europa, seen here photographed by Voyager 1, is the second closest of Jupiter's main moons. It has a very smooth surface with few craters and no volcanoes, but features distinct long markings. Scientists believe that it is posible that liquid water, heated by tidal energy, exists beneath Europa's icy surface, making it a posible home for extraterrestrial life. A tenuous oxygen atmosphere also exists. This computer generated, false colour image of Europa shows red line features thought to be cracks in the moon's water ice crust.
© National Aeronautics & Space Administration / Science & Society