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This is an image of the surface of Io, looking down on a volcano and the lava plain surrounding it.
Click on image for full size

Surface of Io

The surface of Io is completely volcanic, with lava flows of sulfur from the interior, as shown in this image. White patches in the image indicate areas of surface SO2 frost.

The heat for this volcanism stems from tidal forces due to the unique position of Io relative to Jupiter and the other moons. Io is a small moon, very close to Jupiter, and well inside the other 3 main moons. Io feels the gravitational pull first of Jupiter, then of the outside moons when they sweep by. The alternating pull of gravity has a push-me, pull-me effect on Io, which deforms the moon, and warms it just the way a coat hanger warms when you bend it first one way, then the other way.

Due to this warming, the surface of Io has many volcanoes,.

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Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF