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This is an image of Io.
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Io was first discovered by Galileo in 1610, making it one of the Galilean Satellites. Of the 60 moons it is the 5th closest to Jupiter, with a standoff distance of 421,600 km. It is the 4th largest moon of Jupiter, with a diameter about 2/3 the distance across the United States, of 3630 km (2256 miles).

Io is named after one of Jupiter's many lovers, from Roman mythology. It is the only moon known to have active volcanism, which is visible on the surface.

Io is mostly made of sulfur, iron, and silicates, which means that Io is nothing at all like the other icy satellites of Jupiter, and has had a very different evolution.

The particles comprising Io's atmosphere readily find their way into the magnetosphere, and create a donut-shaped cloud called the torus. This cloud has a very profound effect on Jupiter's magnetosphere.

Because of all the volcanic activity, the environment of Io is pretty inhospitable to life as we know it.

Last modified September 16, 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