Metal, rock, ice?


  • Elaine Friebele


Observations during two of Galileo's recent encounters with Jupiter's moon Europa suggest that its 100–200-km-thick outer shell is mostly ice and water. “We know that Europa has a very deep layer of water in some form, but we don't yet know whether that water is liquid or frozen,” said John Anderson, a planetary scientist at NASA's Jet Propulsion Laboratory, who reported the results with coworkers in the May 23 issue of Science. The measurements also indicated that Europa's deep inner core is very dense and may consist of either metal surrounded by rock or a mixture of metal and rock.

In the same issue of Science, Margaret Kivelson of the University of California at Los Angeles reported possible evidence of a magnetic field on Europa based on magnetometer data from Galileo's pass in December 1996.