Pluto may lose its "planetary" status

Originally Posted by Acro-nym

Does Pluto have an atmosphere? I mean, given that they'd established Charon is a satellite, I can see why it couldn't be a planet. Part of the definition of a planet, if I remember correctly, is that it has to have atmosphere. Thus, these asteroids and moons that people may have wanted to become planets due to their size just don't fit the criteria.

That's one of the reasons why New Horizons was launched to Pluto. Pluto is believe to have a temporary atmosphere. Once it's reached out far enough, it sublimes onto the surface because of the sheer cold at such distances. By getting nearer to the sun, such as when it has crossed Neptune's orbit, it's enough heat to sublime back into a gas. New Horizons is supposed to investigate it right around when this freeze happens.

Originally Posted by guyinrubbersuit

Mercury doesn't have an atmosphere and it's still a planet.

Oh yes it does. A very thin one that is made up of the particles blasted off the surface from impacts and solar wind. The heat allows for the thin veil to escape the planet very easily. Go check it out at Nine Planets.

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