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The Universe at Your Fingertips 2.0 DVD from the Astronomical Society of the Pacific is in our online store, filled with Earth and space science resources.
This is a cutaway drawing of the proposed structure of Ganymede's interior.
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Differentiation is a scientific term which really means "to separate". In their earliest history, elements which made the planets would part into separate regions, if the planet were warm enough. This is the akin to the process whereby an oil & vinegar salad dressing will part into regions made only of oil and only of vinegar.

Planetary elements which separate include iron, which is heavy and silicate rock, which is lighter. Iron falls to the center of a planet and forms a core, silicate material stays in the middle, ice stays near the top, as shown in this drawing of the moon Ganymede.

Earth/Mars are examples of contiguous planets which did/did not differentiate early in their histories. Ganymede/Callisto are examples of contiguous moons which did/did not differentiate early in their histories. The lack of differentiation may say something about how warm these planets were upon formation.

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Our online store includes issues of NESTA's quarterly journal, The Earth Scientist, full of classroom activities on different topics in Earth and space science, ranging from seismology, rocks and minerals, oceanography, and Earth system science to astronomy!

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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