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This drawing shows the possible interior of Callisto.

Interior of Callisto

When the Galileo spacecraft flew by Callisto, it made measurements which showed that Callisto was made almost entirely of the same thing. This means that Callisto never separated into layers, but is probably formed of a unusual material which is made of rock and ice combined. The fact that Callisto never separated, early in its history, probably means that Callisto never warmed up after formation.

At the same time, there were some measurements that suggested that there might be a thin salty-slushy layer of watery-ice that creates current. Water supports current. That is why people donít drop electric appliances into the bathtub! An instrument on the spacecraft that is sensitive to current measured something that, like on Callisto, suggested a watery layer was present on Ganymede and Europa as well.

This is a picture that shows the interiors of Io, Europa, Ganymede and Callisto together.

Last modified September 19, 2003 by Jennifer Bergman.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA