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Saturn's A-ring Soaks Up Debris Ejected from Nearby Moon
ScienceDaily is running a story about the recently discovered interaction between Saturn's A-ring and one of Saturn's small moons, Enceladus. Thanks to data from Cassini, scientists have discovered that ejected matter from Enceladus' ice geysers is absorbed into the A-ring, where it is then trapped. We discussed the geysers themselves a few years ago, and researchers have been working since then to determine where the material was going. Quoting:
"This is the latest surprising phenomenon associated with the ice geysers of Enceladus to be discovered or confirmed by Cassini scientists. Earlier, the geysers were found to be responsible for the content of the E-ring. Next, the whole magnetic environment of Saturn was found to be weighed down by the material spewing from Enceladus, which becomes plasma -- a gas of electrically charged particles. Now, Cassini scientists confirm that the plasma, which creates a donut-shaped cloud around Saturn, is being snatched by Saturn's A-ring, which acts like a giant sponge where the plasma is absorbed."
I often have the same problem with Enchiladas and my A-ring.
To put it more exactly, tidal forces will tear apart anything within, roughly, the A ring. (Cavaets: this applies to bodies with no internal cohesion and cases where there's a large size differential move the limit inward, a la Porco et al. 2006.)
Tides are a big problem for forming a moon within, roughly, the A ring. A bigger problem is that Enceladus produces "dust" (very small particles, the size of particles in cigarette smoke, approximately), albeit made mostly of ice. It takes a long time to form this stuff into macroscopic bodies when the conditions are friendly (which they aren't). Worse still, Enceladus isn't really putting out that much mass per time. It'd take a very long time to put out enough to make another decent-sized moon, even at 100% efficiency.
Don't make us come over there: http://xkcd.com/307/
The debris being generated cannot form into a new moon, as the A-ring is within the Roche radius of Saturn.
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I'm not sure that this is really news. I can vaguely recall people talking about exactly this sort of thing happening in papers from years ago. I'm not 100% certain that the topic was E ring particles, but I rather thing that it is. Sure, before we found the plume on Enceladus, that moon's connection wasn't apparent, but the issue of contamination of the A ring has come up before. I even remember discussion as to how far into the A ring you'd have to go before the contamination stopped. (Which probably played back into older photometric and spectroscopic measurements of the outer A ring, which has a a rather distinct character.)
It's a bit difficult to tell from the article what the point of the new research is, but I will say that even confirming this with new, perhaps more telling, measurements is still useful result, even if I'm remembering correctly and this isn't a new idea.
No. With the exception of the E ring, all of Saturn's rings are within its Roche Limit. Tidal forces would prevent a new moon from forming that close just as they'd break up an existing one.
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heh heh "A-ring" heh heh "Moon" heh heh heh...
I don't therefore I'm not.
Do they really look like geysers to anybody? Wouldn't they be more columnar, or conical?
... 2 years ago, same story - with a cometary conclusion:
If anything it looks like the solar corona, or a comet perhaps?
ahh, here we go
http://www.astrobio.net/news/modules.php?file=article&name=News&op=modload&sid=1797
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You don't need collisions for such viscous spreading (and most stuff wants to move inward anyway). Also, the A ring is somewhat held in check by the larger moons, so spreading is very slow.
IANAAP, and I'm not disagreeing with the basic point of what you are saying, but...
from the link you provided, the radius of the Roche limit (1) depends on the structural integrity of the satellite, not just a constant radius from the stronger body, and thus (2) does not apply at all to the pulverized bits of the weaker body.
The Saturn A ring therefore decorates a particular Roche limit that applied to some other body that was pulverized in the past, and not a guaranteed "point of no moons" around Saturn. If the Roche limit were not based on the structural integrity of the moon, then even the broken boulders of an ex-moon would be further pulverized into rocks, then sand, and finally nano-dust. If a boulder survives inside the original body's Roche limit, it must be because it has a new Roche limit that is closer to Saturn.
While I admit that the pulverized bits are unlikely to coalesce into a moon, I wouldn't say they're impossible. If something were to cause a strong self-attractive force, say, some ionizing comet or who knows, the FSM's noodly appendages, a moon that developed into a highly rigid structure could continue to survive there. If we someday mine asteroids in the region, structural integrity of manmade or man-inhabited objects will obviously be of prime importance.
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