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Fraser
2005-Mar-17, 05:40 PM
SUMMARY: NASA's Cassini spacecraft has made a surprising discovery about Saturn's moon Enceladus: it has an atmosphere of water vapour. Cassini detected the atmosphere during both of its recent close flybys. Scientists are sure what's causing this cloud of water vapour, but it could be caused by volcanoes, geysers, or gasses escaping from the moon's interior. Enceladus' gravity is very small, so it wouldn't be able to hold onto an atmosphere for very long. This means there must be some continuous source replenishing it.

View full article (http://www.universetoday.com/am/publish/enceladus_atmosphere.html)

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lswinford
2005-Mar-17, 08:16 PM
Couldn't hold a water vapor atmosphere very long because of low gravity? How about low temperatures? I expect that sunlight sublimates ice crystals (water ice going from solid to vapor, particularly when the crystals lense the light to a focal point in or on the crystal so as to provide the energy for the physical phase jump) and they then fall in snow back down on the surface as it turns away from the light.

Greg
2005-Mar-17, 10:13 PM
I agree with that. Temperatures are so cold out there that the presence of water vapor implies that volcanism is the source. The high reflectivity of the surface of course sugests that the vapor crystallizes as snow and ice on the surface later.
My question is why is such a small moon so geologically active. I imagine the answer must be tidal heating. If so, this would be another good example of how life as we know it could get a foothold in a seemingly unihhabitable region of the solar system.

TuTone
2005-Mar-18, 12:00 AM
Interesting, what makes a world active? Why can't a world just be composed with no volcanic eruptions?

rabeldin
2005-Mar-18, 12:19 AM
Gravity usually causes tides of some sort on satellites. I imagine Saturn's gravity causes tides even within its satellites. That could heat things up a bit.

wstevenbrown
2005-Mar-18, 03:23 AM
hmmm... 'significant', but no density estimate. Still, since detection was by means of magnetometers, resupply is very likely by sublimation, transport is by following magnetic field lines. Expect to see higher density 'atmosphere' on the dayside, fading surface streaks on the nightside, as charges recombine and gravity takes over. Print. Erase. Print. Erase. Like the polar patterns on Mars, but more gradual and diffuse. zzzzz ;) Steve