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This is a composite image of the interior of the Galilean satillites.
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Warming of an Icy Moon from Inside

If the satellite has means of warming itself, then the interior may go through many startling changes as the moon evolves. The moon may change its size, and grow or shrink as the layers inside go through stages of freezing or warming. The moon may also have water inside, and water may exist close enough to the surface to produce conditions favorable for life.

The moon will exhibit proof of all these interior changes in it's features on the surface.

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Cool It! Game

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Evolution of the Interior of Icy Moons

No one really knows how a moon changes as it gets older. The moon may change it's size, and/or have water oceans inside as it changes. The graph to the left predicts what kind of ice occurs inside the...more

Amalthea

Amalthea was discovered by E Barnard in 1872. Of the 17 moons it is the 3rd closest to Jupiter. Amalthea is about the size of a county or small state. Amalthea is named after the goat in Greek mythology...more

Callisto

Callisto was first discovered by Galileo in 1610. It is the 2nd largest moon in the solar system, and is larger than the Earth's moon. It is about as big as the distance across the United States. Callisto...more

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...more

Very Large Impact Crater

Many different types of surface are shown in this picture. In the front is a huge crater, which goes for a long way over the surface. This crater could be compared to that of Mimas. They both show that...more

Surface of Callisto

The surface of Callisto is deeply marked with craters. Craters are the little white marks in the picture. It looks like it might be the most heavily cratered body in the whole solar system. And some of...more

Europa

Europa was first discovered by Galileo in 1610, making it one of the Galilean Satellites. It is Jupiter's 4th largest moon, 670,900 km ( miles) from Jupiter. Europa's diameter is about half the distance...more

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