Titan - Ganymedes

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aerogi

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Hello all! I'm a newbie and altough space and astronomy is one of my favourite interests, I'm not an expert on the matter... so here's a first question I have for some time now.<br /><br />How come that Titan has such a dense atmosphere and Ganymedes has no atmosphere at all? is there an explanation for that? Did it ever had an atmosphere? <br /><br />Thanks!
 
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remcook

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One reason I can think of is that Ganymede is warmer than Titan, since it closer to the Sun. because of this, the molecules have more energy and escape more easily from the gravity field of the moon.
 
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titanian

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I also think ( as well as James Jeans) that the temperature at this distance from the Sun is the main factor to what we can call the "Titan Paradox" but there might be be other factors( how fast it rotates, volcanism...).You can refer to the following web site for attempts of explanation: www.titanexploration.com<br />Note that the theoretical temperature at the surface of a dark body orbiting the Sun at the same distance as Titan is only (around) 30 degrees lower than the theoritical temperature at the same distance as Ganymede.This would have made the difference for the amazing stability of the titanian atmosphere.
 
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odysseus145

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Could the intense radiation from Jupiter have prevented its moons from forming an atmosphere? <div class="Discussion_UserSignature"> </div>
 
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CalliArcale

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Possibly, but the solar wind ought to have even more of an affect on an atmosphere. A moon within its parent's magnetosphere would be protected from the worst of the solar wind, but counter-intuitively, Titan is only sometimes within Saturn's magnetosphere.<br /><br />Of course, another possibility for Titan's atmosphere is that it may be continuously replenished from within, but I'm not sure how; it's pretty dense.<br /><br />BTW, Ganymede does have a very thin atmosphere (probably roughly comparable to that of our moon, which is so thin it can easily be considered a vacuum; it's considerably thinner than the Earth's atmosphere at the ISS's altitude!), which may be produced by the continual bombardment of the moon by the solar wind. It is constantly being lost, however. Io has a more significant atmosphere, constantly replenished by Io's volcanoes, but it, too, is continually being lost to space. Io's constantly shedding atmosphere is trapped into the Io torus around Jupiter, and may actually be responsible for renewing at least some of the material in Jupiter's faint ring system. Europa also has an incredibly thin atmosphere. These atmospheres are quite unlike that of Titan, however. <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em>  -- The Tenth Doctor, "Blink"</font></p> </div>
 
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aaron38

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Is there an exact definition of an atmosphere? Some sort of lower pressure bound?<br /><br />A puddle is not an ocean. It doesn't seem right for a few atoms near a moon's surface to be called an atmosphere. But then, maybe there isn't any better name for it.
 
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Saiph

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I don't think there's a limit.<br /><br />IIRC they described the apollo landing craft as depositing more gas than the moon's atmosphere (or something like that).<br /><br />That implies a really low limit, if there is one. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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