Pluto & Charon

• Pluto is actually smaller than Neptune's largest moon, Triton
• Pluto's only known moon, Charon, is almost half its size.  Because of this, astronomers sometimes look at them as a 'double-planet system'. 
• They are both dark, featureless worlds made of rock and are extremely cold.  You would freeze before you got as far as them.  
• So far, no spacecraft has landed on the surface of Pluto or Charon and so we are not really sure what the surface looks like.  It is the only planet which has not yet been visited by a spacecraft.
• Pluto was not discovered until 1930.  It is the smallest planet in the solar system.
• While Pluto is closest to the Sun, the methane and nitrogen frozen at its poles thaw out, and temporarily form an atmosphere.  As it moves away from the Sun again, the atmosphere freezes and falls back to the planets surface.

< 'Double Planet'

Some scientists consider Pluto and Charon to be a double planet, as Pluto's atmosphere appears to extend out to include Charon, suggesting that they may share it.

Pluto and Charon >

Other astronomers do not believe Pluto is a real planet at all, but may be a moon which escaped from Neptune's gravitational pull.

What do you think?