Europa

2. Europa Information From http://solarsystem.nasa.gov

3. Europa Intro • Jupiter's icy moon Europa is slightly smaller than the Earth's Moon. Like the Earth, Europa is thought to have an iron core, a rocky mantle and a surface ocean of salty water. Unlike on Earth, however, this ocean is deep enough to cover the whole surface of Europa, and being far from the sun, the ocean surface is globally frozen over.

4. Four hundred years ago, the astronomer Galileo's discovery of Jupiter's four large moons forever changed humanity's view of the universe, helping to bring about the understanding that Earth was not the center of all motion. Today one of these Galilean moons could again revolutionize science and our sense of place, for hidden beneath Europa's icy surface is perhaps the most promising place to look for present-day environments that are suitable for life.

5. These cracks had separated, and dark, icy material appeared to have flowed into the opened gaps, suggesting that the surface had been active at some time in the past. Voyager images showed only a handful of impact craters, which are expected to build up over time as a planetary surface is constantly bombarded by meteorites over billions of years until the surface is covered in craters. Thus, a lack of large impact craters suggested that the moon's surface was relatively young and implied that something had erased them - such as icy, volcanic flows, or settling of the icy crust under its own weight.

8. Scientists also found that the patterns of some of the longest linear features on the surface did not fit predicted patterns of fractures that should be created by tides as Europa orbits Jupiter. They determined that the patterns would fit very well if Europa's surface could move independently and was not locked to the rest of the interior, as would be the case if a layer of liquid or slightly warmer ice existed between the crust and deep interior.

9. Ridges criss-cross the surface, and are places where warm ice or water has pushed up the surface or erupted. Some ridges are cycloidal in shape, arcing across the surface: these probably formed along cracks that were influenced by the rising and falling tides. Bands are places where the icy surface has pulled apart, with new warm ice rising up, chilling, and cracking. Some water-filled cracks, or dikes, could shoot upward from the base of Europa's ice.

10. Thrace Macula • Thrace Macula is the largest dark spot on Europa and has been recently modified and resurfaced. The nature of the dark material is uncertain but may have a higher concentration of salts or sulfates associated with the water ocean lying perhaps around as few as 6 miles (10 kilometers) beneath the surface. Some of this dark material appears to have ponded in low areas indicating that some liquid might be involved.

12. The Conamara Chaos • The following image is a view of a small region of the thin, disrupted ice crust in the Conamara region of Jupiter's moon Europa showing the interplay of surface colors with ice structures. The white and blue colors outline areas that have been blanketed by a fine dust of ice particles ejected at the time of formation of the large, 26 kilometer (16 mile) in diameter crater Pwyll some 1000 kilometers (621 miles) to the south. The unblanketed surface has a reddish brown color that has been painted by mineral contaminants carried and spread by water vapor released from below the crust when it was disrupted. The original color of the icy surface was probably a deep blue color seen in large areas elsewhere on the moon. The image covers an area approximately 70 by 30 kilometers (44 by 19 miles).

15. Europa's Churning Ice Shell (Labeled Version) • Europa's bizarre surface features suggest an actively churning ice shell above a salty liquid water ocean. This artistic composite illustrates Europa's many different types of surface features and the interior processes that might form them.Heat is created within the floating ice shell by flexing and squeezing due to rising and falling tides as Europa orbits the giant planet Jupiter. It is this tidal heat that keeps the ocean liquid at a temperature near 0 degrees Celsius (32 degrees Fahrenheit), even though the surface is frigidly cold at a temperature of about -170 degrees Celsius (-275 degrees Fahrenheit). The cold near-surface ice can crack or crumble, while the tidal heat keeps the base of the ice shell close to the ice melting temperature, so the ice there can slowly flow, like a glacier.

16. Blobs, or diapirs, of relatively warm ice may slowly rise from the base of the floating ice shell to the cold near-surface ice, and they might melt and expel salts in their path. Diapirs might push the surface upward to create domes, or crumble the surface and erupt to form spot. Diapirs might merge and tidal heat can concentrate within the ice shell, perhaps partially melting it, to create the jumbled blocks of chaos terrain. Ice diapirs could be a sign of convection within the ice shell, like the rise of warm rock within the Earth's mantle.

17. Europa's surface shows few large impact craters, indicating that vigorous geological activity has wiped out the older ones. A large impact with bull's-eye rings may have once punched all the way through the ice shell to the watery ocean, though the icy hole has since healed.Europa's churning ice shell could allow surface contaminants to move downward into the ocean. It can also dredge up deep slushy ice, allowing material from the ocean -- including life, if it exists there -- to be carried to the surface.