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This is an drawing of the Galileo probe exploring Jupiter's environment.
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Image from: The Jet Propulsion Laboratory

The Atmosphere of Icy Moons

It is unlikely that the icy moons have an atmosphere. The reason they have no atmosphere is because they do not have enough gravity. Gravity depends upon the amount of substance (mass) contained in a body. The smaller the body is the lower its gravity, so moons have much less gravity than a planet has. The icy moons are made of ice, and because ice contains less substance than rock, icy moons have even less gravity than a rocky moon of the same size. Because there is little gravity, an icy moon cannot hold onto an atmosphere for very long.

An atmosphere can come from inside a moon. Some icy moons may have active surfaces, such as Europa, where the surface may "crack" and release molecules for an atmosphere from inside the moon.

However they get there, molecules may float around a moon for a while, but because of the low gravity, whatever "atmosphere" may be created rapidly drifts away.


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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