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Europa: The Facts
By Robert Roy Britt
Senior Science Writer
posted: 11:29 am ET
26 January 2000
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europa_core_000126 Europa has a core of iron and nickel (shown in gray in the image above) surrounded by a rocky shell (brown). A shell of water in ice or liquid form (blue and white) surrounds the rock layer. The surface layer is shown as white. The smallest of the four Galilean moons (the others are Io, Ganymede and Callisto) Europa is about the size of Earth's moon. Europa seems to contain a vast ocean of beneath its surface that may be liquid. But with a surface temperature of minus 260 degrees Fahrenheit (minus 162 degrees Celsius), it's hard to imagine how there could be liquid below, as many scientists believe. Jupiter itself may hold the clue: Its vast gravity could be tugging at Europa's sub-surface, creating enough warmth to keep large parts of its ocean liquid. Scientists call this "tidal friction," and it's the same process thought to spur intense volcanic activity on Io. Brown ridges on Europa's surface are thought to be frozen remnants of cold volcanoes, which occur when liquid or partially frozen water erupts to the surface. Europa is 1,950 miles (3,138 kilometers) in diameter. It is 416,900 miles (670,936 kilometers) from Jupiter, orbiting once every 3.6 days.
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