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This drawing shows the evolution of Callisto.
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Evolution of Callisto

Measurements by the Galileo spacecraft have been shown that Callisto is the same inside from the center to the surface. This means that Callisto does not have a core at the center.

This means that, unlike Ganymede, Callisto probably never warmed up enough while it was forming to allow for the materials inside to separate.

The lack of warmth prevented any movements of the crust which would have changed the appearance of the surface over time.

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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