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selvaarchi
2015-Apr-18, 02:27 AM
Do you know which moons have atmosphere? To answer that question you must first decide what is an atmosphere. Emily defines it as "atmospheres dense enough for weather." So do you have an answer to the question? Read the article by her for the answer.

Charon is not on the list but my money is on it being included in the next 3 months:D

http://www.planetary.org/blogs/emily-lakdawalla/2015/04081101-a-moon-with-atmosphere.html


What is the solar system moon with the densest atmosphere? Most space fans know that the answer is Titan; with a surface atmospheric pressure of 1.4 bars, its air is thicker than Earth's. A few of you might know that Triton's is the next densest. But what's the third? Fourth? Do any other moons even have atmospheres? In fact, they do; and one such atmosphere has just been discovered.

No other moon's atmosphere is quite like Titan's smoggy sky. From space, we can see straight to the other moons' surfaces, with no clouds or haze in the way. Most moons' atmospheres are extremely tenuous, so much so that their constituent molecules never collide with each other. Such collisionless atmospheres are called exospheres. The Moon has an exosphere, as does the planet Mercury.

A very few moons have atmospheres that are dense enough for their gas molecules to collide with each other. This can happen even in a pretty thin atmosphere. Triton's had a surface pressure of 14 microbars when Voyager 2 flew by. As the seasons have progressed on Triton the atmospheric pressure has increased by a factor of three or four, but it's still 20,000 times less dense than Earth's. Still, when air molecules can collide, you can have wind, and even weather. Such an atmosphere can also offer a moon's surface some protection from the particles flung around in giant planet magnetospheres. You can see on Triton how upper-level winds blow the tops of its geysers away. If we're very lucky, we'll see similar features when New Horizons passes Pluto this summer. (Pluto's atmosphere is denser than Triton's.)

Swift
2015-Apr-18, 01:43 PM
I've moved this thread from Space Exploration to Astronomy (even with the reference to New Horizons)

tony873004
2015-Apr-21, 06:34 AM
Do you know which moons have atmosphere? To answer that question you must first decide what is an atmosphere. Emily defines it as "atmospheres dense enough for weather." So do you have an answer to the question? Read the article by her for the answer.

Charon is not on the list but my money is on it being included in the next 3 months:D

http://www.planetary.org/blogs/emily-lakdawalla/2015/04081101-a-moon-with-atmosphere.html

All of them... and none of them (except Titan). It depends on what you mean by 'atmosphere'. By Emily's definition, only Titan, whose atmosphere at the surface is denser than Earth's. For the rest of them... the vacuum chamber in my classroom has them beat by probably a few orders of magnitude. I hope Charon is the exception, but I doubt it.