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With Explore the Planets, investigate the planets, their moons, and understand the processes that shape them. By G. Jeffrey Taylor, Ph.D. See our DVD collection.
This is an image of Pluto with its moon Charon.
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Image courtesy of NASA/JPL. This image is in the public domain.

Pluto & Charon, a double planet

Of all the planets and moons in the solar system, Pluto and Charon are the two which are the most alike. They are almost the same size, and they are very close together. Pluto and Charon are so close that they may even share an atmosphere. Air may be drawn from Pluto by the gravity of Charon to reform on Charon.

The only other planet and moon in the solar system which could be a double planet are the Earth and the Moon. The origin of such a double planet is hard to explain. The best explanation may be that some large object struck Pluto (and the Earth) and tore out a blob which became Charon (and the Moon) from the crust of the planet.

In the case of the Moon, the Moon seems to be made of rock which is very much like the Earth's crust and not like the Earth's iron interior. Likewise Charon may be made of more icy material which looks like Pluto's surface, rather than the more rocky interior of Pluto.


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Charon - Pluto's biggest moon

Charon is a moon of Pluto. Pluto has // Call the moon count function defined in the document head print_moon_count('pluto'); moons. Charon is much bigger than Pluto's other moons. James Christy discovered...more

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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