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Fraser
2005-Apr-27, 05:27 PM
SUMMARY: NASA's Cassini spacecraft has discovered an unusual cloud of particles around Enceladus, one of Saturn's many moons. They could be stray particles from Saturn's outermost E-ring or a previously unseen dust cloud. The discovery is so interesting to researchers that they'll have Cassini change its altitude on its next flyby - scheduled for July 14 - lowering the spacecraft so that it passes only 175 km (108 miles) above the surface of the moon.

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

What do you think about this story? Post your comments below.

piersdad
2005-Apr-27, 07:49 PM
175 kilometers fly by
and the moon is 500 km diameter
thats not a fly by its a mear miss.
I wait with bated breath for the next near miss

lswinford
2005-Apr-27, 08:48 PM
In the article it said, "The amount of gravity it exerts is not enough to hold an atmosphere very long. Therefore a strong, continuous source is required to maintain the atmosphere." What makes them think that this is a "continuous" phenomenon? I could see, ala Mt. St. Helens or any of a hundred others, how pressures could build, as discussed, and an eruption happen, followed by a period of relative dormancy until the next critical degree of pressure develops (also a common geyser could be an example). We may just happened to have had a probe in the right place and the right time, or is there more to the picture?

I also hope that "dust" is pretty dusty, not clumpy, and we blink when passing through or we may have pitted lenses or worse. :blink:

VanderL
2005-Apr-27, 09:15 PM
I haven't seen any calculations, but I would be very surprised if any "gravitational flexing" could produce geysers on a moon only 500 km in diameter. More likely the dust is electrically "machined" from it's surface. This would work in the highly magnetic/electric environment of Saturn, and is maybe even strong enough on this and other (atmosphere-less) moons to produce and maintain the rings. It is known the rings are an active part of the magnetosphere, so it wouldn't be a big leap to assumeelectromagnetic forces could be responsible for dust "emission" from a moon's surface.

Cheers.

wstevenbrown
2005-Apr-27, 10:48 PM
More likely the dust is electrically "machined" from it's surface.

I think you are needlessly complicating matters. Even at low intensity, solar radiation still has a percentage of high-energy photons sufficient to cause sublimation of water and other solids of low molecular weight. Some of them will even be dissociated or ionized, in which case, because of the very low gravityand lack of other atmosphere, they will drift with the local magnetic field. The field does not cause the particles, it only transports them. They either recombine and fall to the surface, or get hit again while aloft and enter the orbital plane to become ring material. The process is supplemented by meteor spalls. These processes are prosaic for small worlds-- they don't need to be sensationalized.

This is clearly an ongoing process, continually resupplying particles. If your 'electrical machining' is going on, where are the actinic flashes? Where are the fulgurites? Why are Cassini's magnetometers not fried by the overload?

If the only tool in your box is a hammer, everything starts to look like a nail.

Best regards-- :P Steve

VanderL
2005-Apr-28, 08:17 AM
This is clearly an ongoing process, continually resupplying particles. If your 'electrical machining' is going on, where are the actinic flashes? Where are the fulgurites? Why are Cassini's magnetometers not fried by the overload?


Good questions, but the magnetometers wouldn't show much unless it was measuring at the moon's surface. Fulgurites are small features, have various shapes, and thus would need to be sampled on-site. (btw Mars should also show fulgurites, and the rovers could find that out).
If the surface is producing the particles through sunlight, why is only Enceladus showing a cloud (called strange by the researchers, hopefully not just for PR reasons), and not every other object without a significant atmosphere. I think the cloud can be likened to comet dust. Would be interesting to compare the particles.

[/b][/quote]I think you are needlessly complicating matters.


[quote][b]If the only tool in your box is a hammer, everything starts to look like a nail.

Both possibly true, but the same applies to the explanations offered thusfar B)
I don't want to turn this discussion into something that should be in the alternative section. So maybe I'll post it there as well.

Cheers.

Nick4
2005-Apr-28, 03:28 PM
Thats cool i wonder what we will find.

lswinford
2005-Apr-28, 07:56 PM
Ah, some new words to look up, ( or is it look up again? ) actinic and fulgarites. Thanks.