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Enceladus Jet Sources
Doc
post Jun 25 2009, 06:42 PM
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The current understanding of the geysers of Enceladus

One says that the presence of Na salts in the E-ring implies an ocean on Enceladus.

Another group says that Enceladus has as much Na (note here they are mentioning the plumes) as there is in a glass of relatvely pure water (metaphorically speaking). So they suggest that the plumes are rather like an air conditioner set to gentle breeze rather than geyser speed rolleyes.gif

Now a question, how do you connect gigawatts of heat energy incorporated in the plumes with gentle breeze speed? unsure.gif


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john_s
post Jun 25 2009, 08:30 PM
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A clarification- according to the "misty caverns" idea, the water vapor evaporates from the salt-water interface at a slow, gentle rate, but over a large area, and by doing so it builds up pressure in those chambers, and then it rushes out the "leaks" in the narrow fractures beneath the tiger stripes at supersonic speeds, plenty fast enough (we think) to keep the surface warm. The speed of ejection from the surface is similar in the "geyser" model and the "misty cavern" model- the difference is just whether liquid water is involved near the surface.

The slow evaporation from large water surfaces was an idea that originated with the CDA team, in fact, but it helps nicely to reconcile the two data sets.

We put together a graphic as part of the Cassini web release that I hope explains the options in a somewhat comprehensible form. The different interpretations have proved tricky to explain to people, and of course there may be even better models that we haven't thought of yet. So further suggestions are welcome!

John.

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post Jun 25 2009, 08:38 PM
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John, just for baseline purposes, what's the latest leading model for Enceladus' heat source? Was a single specific type (localized radioactive, global tidal with a south polar soft spot, etc.) postulated to derive these plume models?


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john_s
post Jun 25 2009, 09:29 PM
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It's gotta be tidal heat- radioactive heat isn't nearly enough. The questions involve where the heat is dissipated (in shallow fractures? More broadly throughout the south polar ice shell?) and what's happening with its orbit, and its interaction with Saturn and Dione, to keep the heating going.

John
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post Jun 25 2009, 10:56 PM
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QUOTE (john_s @ Jun 25 2009, 02:29 PM) *
The questions involve where the heat is dissipated (in shallow fractures? More broadly throughout the south polar ice shell?)


Is it fair to say, then, that the primary constraint on plume models might be the thickness of the ice shell? Seems like that would be largely a function of the amount of tidal heating.

Re the localized nature of the plumes: Too bad that a decent gravimetric map of Enceladus seems pretty difficult to obtain. Willing to bet that there's some sort of asymmetry in the rocky part to account for this.


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john_s
post Jun 26 2009, 06:30 AM
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Ice shell thickness is important, though the thickness of the cold, brittle, surface layer versus the warm, ductile, regions is maybe the most important thing. That's not just a matter of total heat flow, it's a matter of how the heat is distributed, too.

We'll be getting some gravity data next Spring, and some more in the XXM if that's approved by NASA. So we may have some constraints before too long.

John
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belleraphon1
post Jun 26 2009, 11:31 AM
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This is not scientific, but I love the "misty caverns" model.... imagine spelunking those! Really love how mysterious and complex Enceladus is... so much to learn.

So glad amateurs like myself have unmannedspaceflight to help in these journeys.

Thanks all!!!

Craig
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Juramike
post Jun 27 2009, 01:39 AM
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Enceladus Wharrgarbl
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nprev
post Jun 27 2009, 01:53 AM
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laugh.gif ...Yeah, that poor mutt might get one Wharrgarbl out before he froze solid!


Good news re gravity data, John, thanks! More reason than ever to root for the XXM. I don't see any way to crack this nut short of getting that, and given the tiny size of Enceladus I'm betting that there will be a substantial anomaly in mass distribution...at least one.

Keep hearing 15GW as the heat output, and not sure what that number signifies or how it's derived. Only thing I can think of is that's the energy needed to fire off the observed plumes and therefore doesn't really set a limit on the total amount of global heat production? The ice shell structure would presumably be a function of total heat output since ice/water is such a good heat sink...


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marsbug
post Jul 1 2009, 12:45 PM
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Some interesting stuff at the planetary society and some tantalising abstracts.


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marsbug
post Jul 16 2009, 12:22 PM
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Interesting report on spaceref.


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Ron Hobbs
post Jul 22 2009, 09:08 PM
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Ammonia, at last.

Saturnian Moon Shows Evidence of Ammonia
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HughFromAlice
post Jul 23 2009, 09:24 AM
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A longer report at Physorg.com http://www.physorg.com/news167498118.html

Also ....."The fact that we found a lot of argon 40 also argues for liquid water," Lunine said. Liquid water most likely circulating through Enceladus' rocky core is the best explanation for all the argon 40 detected, he said.

And there was (reconfirming earlier detection) ....."an abundance of carbon-bearing molecules, or "organics," entrained in the water vapor.......... (such) as methane, formaldehyde, ethanol and hydrocarbons."

What's the limit of detecting/identifying heavier carbon molecules? Very interesting they have got this far in their analysis. Roll on the Nov flybys!!
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Ron Hobbs
post Aug 26 2009, 05:29 AM
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QUOTE (belleraphon1 @ Jun 26 2009, 04:31 AM) *
This is not scientific, but I love the "misty caverns" model.... imagine spelunking those! Really love how mysterious and complex Enceladus is... so much to learn.


I listened in on the CHARM teleconference with Postberg today, and he seems to think it is very scientific. PDF Presentation

He made what seems a strong case that the distribution of particles in the E-ring must come from pools of effervescent liquid salt water within a kilometer or two (or less) of the surface of the south pole. Depending on how much convection there is, the pools are likely to have a total area of hundreds to thousands of square kilometers. He has a slide of Terran ice caves and hypothesizes complex arches and pillars in the gravity field that is little more than 1% of that on Earth.

I am sure that there will be further debate, but the image that he suggests is a very "mysterious and complex" environment. I can't wait until the the artists run with this vision.
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belleraphon1
post Aug 26 2009, 12:22 PM
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Thanks for the heads up Ron!!!

Slide 19.... wow...imagine wandering the caverns on Enceladus, spotlight in gloved hand. The light cacscading off the crusty ice arches! That would be a numinous experience!

Craig
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