This is an image of Pluto with its moon Charon.
Click on image for full size
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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