We discussed Europa's icy surface and possible sub-surface ocean last week. Some images that Galileo sent back showed bumpy features on Europa's surface, almost like blisters. These features (shown below) look similar to places on Earth where glaciers sit on top of undersea volcanoes. Basically, these underwater vents heat the water above them which melts the overlaying ice. Since these volcanoes are not active all the time, there are periods where the water can re-freeze on the surface. This re-freezing does not leave a smooth sheet, but rather a chaotic frozen pattern, much like the pattern seen on Europa. So what does this all mean? It suggests that there is some sort of internal heating mechanism within the moon, and therefore a subsurface ocean! The depth of this ocean, and the thickness of the ice sheet is still unknown, but further observations and hopefully future missions will enlighten us on Europa's mysterious structure.
Thera Macula (false color) is a region of likely active chaos production above a large liquid water lake in the icy shell of Europa. Color indicates topographic heights relative to background terrain. Purples and reds indicate the highest terrain. Image Credit: Paul Schenk/NASA
