If there's one thing space exploration has taught us about moons, it's that they're as diverse and dynamic as the planets they orbit. Nowhere is this more evident than among the gas giants of our outer solar system where the diminished solar heat and water-rich environment allow dozens of ice-covered moons to thrive. Here, spacecraft have helped make valuable discoveries regarding two of our solar system's most frigid satellites: Europa and Enceladus.
One of Jupiter's four largest moons, Europa has intrigued astronomers since its discovery by Galileo in 1610. Its icy landscape was first revealed in 1979 when the Voyager Spacecraft captured images of its smooth frozen crust strewn with long dark streaks. These geological features suggest that beneath Europa's cold shell lies a warm ocean that may be resting on rock -- an environment astrobiologists say is suitable for harboring primitive life. NASA and the European Space Agency plan to launch the Europa Orbiter in 2020 to further investigate this possibility of life biologic life beyond Earth.
Neighboring Jupiter are Saturn and its moon, Enceladus. Most land-based telescopes show Enceladus as a faint dot. But images retrieved by the Cassini Spacecraft portray it more dramatically. Like Europa, it is covered in a thick layer of what is thought to be sea ice. Its stark, white color reflects 100 percent of the sunlight it receives, making it the brightest object in our solar system apart from the sun. From this surface, vapor and ice crystals erupt in jets of water hundreds of kilometers high. Much of this material is then attracted by Saturn's gravity and then incorporated into Saturn's massive ring system.
Europa and Enceladus prove that the satellites of our solar system offer more than splendor. They demonstrate that our understanding of our universe is just as enhanced by a frozen moon as it is by a blazing of a star.