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This is a picture of dry ice (frozen CO2) sublimating.
Click on image for full size
JPL

Sublimation, and How Pluto comes to have an Atmosphere

Because the orbit of Pluto is so strange, Pluto is sometimes close enough to the sun for the ices on its surface to turn to gas. Sublimation describes what happens when a frozen material changes to gaseous form. (Evaporation describes what happens when a liquid changes to gaseous form).

The most common example of sublimation is that of dry ice, which is the common name of frozen CO2. When dry ice is exposed to the air it begins to sublimate, or change to vapor, before your very eyes. This happens to dry ice because at room temperature the frozen CO2 would rather be a gas than frozen solid.

When Pluto comes close enough to the sun, the surface of solid Nitrogen sublimates to produce a substantial atmosphere with winds and clouds. Because the planet is so small, however, it does not have enough gravity to bind an atmosphere for very long. Thus Pluto's atmosphere is being rapidly produced and rapidly lost at the same time. This means that the atmosphere is not in a balanced state.

By 1999, Pluto will leave the vicinity of Neptune and drift further away from the sun in its orbit. As it gets further from the sun it will no longer produce an atmosphere. Thus it will soon be too late for humankind to study Pluto's unique environment. These are good reasons to explore Pluto now.


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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