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Enceladus Plume Search, Nov. 27
ugordan
post Nov 30 2005, 01:38 PM
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QUOTE (jmknapp @ Nov 30 2005, 02:24 PM)
Interesting that at 144,000 km the limb was nearly parallel and on top of the center scratch
*

Of course you meant tiger stripe, cats and scratches reside on a totally different moon tongue.gif

EDIT: So far, have there been any estimates from these recent images on the amount of material released/second?


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jmknapp
post Nov 30 2005, 04:48 PM
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QUOTE (ugordan @ Nov 30 2005, 09:38 AM)
Of course you meant tiger stripe, cats and scratches reside on a totally different moon  tongue.gif

EDIT: So far, have there been any estimates from these recent images on the amount of material released/second?
*


And here I thought it looked like a giant tiger had dragged his claws across the south pole, and deeply!

As for the material, I wonder how much it could really be, as nothing is visible looking down over the south pole (marked with a circle):

NAC image of south polar region

In the "forget what we told you yesterday as fact" department, compare this statement from the latest CICLOPS home page:

"A fine spray of small, icy particles, emanating from the warm, geologically unique province surrounding the south pole of Enceladus and believed now to supply the material comprising Saturn's E ring, was first observed in images taken back on Jan. 16, 2005." http://ciclops.org/index.php?flash=1

...to the statement made back in July by Linda Spilker, the Deputy Project Scientist for the Cassini-Huygens mission:

"The water vapor is very different from the E ring particles themselves. So we have this sort of cloud, patchy atmosphere over the south pole, and then the E ring particles seem to be coming uniformly off of Enceladus, probably through micrometeorite impact kicking up particles. So the vents are not the source of the E ring." http://www.planetary.org/news/2005/0730_En...ripes_Spew.html


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Guest_BruceMoomaw_*
post Dec 1 2005, 12:33 AM
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That last quote was actually a misinterpretation by Emily Lakdawalla of what Spilker told her, which is that there was some evidence from particle distribution that the E Ring particles were coming off Enceladus as a whole rather than from the vents. That particular theory very quickly became inoperative; it's the vents, all right.

What I can't yet discover is whether the stuff being spewed from them is a water/ammonia mixture (as would have seemed logical), or just plain water. I'm still trying to get clarification on this, but Cassini seems to be indicating that much more of the nitrogen of Saturn's moons is instead in the form of HCN than had been previously been believed.
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mars loon
post Dec 1 2005, 12:48 AM
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QUOTE (BruceMoomaw @ Dec 1 2005, 12:33 AM)
What I can't yet discover is whether the stuff being spewed from them is a water/ammonia mixture (as would have seemed logical), or just plain water.  I'm still trying to get clarification on this, but Cassini seems to be indicating that much more of the nitrogen of Saturn's moons is instead in the form of HCN than had been previously ben believed.
*

That is the key question. Are ammonia, HCN, organics present?

Thats the scientific justification for NASA/ESA sending a lander/penetrator to Enceledus in a follow on mission to the Saturnian system
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The Messenger
post Dec 1 2005, 03:17 AM
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QUOTE (edstrick @ Nov 29 2005, 11:24 PM)
What really pushed my buttons in the January images were that the features progressively increased in contrast, narrowed, and sharpened toward the limb, and there were no plumelike features at all on the terminator side of the overexposed and saturated crescent, just the usual trace of camera-fog.

Anyway, I'm not claiming credit.. that goes to the team, paricularly for a very nicely designed imaging sequence that covered all bases and seems to have provided far better information on the venting than can be extracted from the previous images. 

None-the-less, it was a gutzy call at a time when everyone seems to be stuck scratching their heads...including Bruce.
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ugordan
post Dec 1 2005, 08:39 AM
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QUOTE (BruceMoomaw @ Dec 1 2005, 01:33 AM)
What I can't yet discover is whether the stuff being spewed from them is a water/ammonia mixture (as would have seemed logical), or just plain water.
*

I'm certainly not an expert on this, but haven't there been some mentions recently about ammonia being destroyed by UV sunlight practically immediately so that's one of the reasons it hasn't been detected yet? Personally, though, I'm having a hard time imagining such a rapid breakdown rate which would prevent any traces of NH3 to be seen. I could buy that for the Enceladus' surface spectra which obviously gets a lot of sunlight, but these plumes should conceivably escape from the interior fast enough to bring some ammonia high up before it breaks down. Which makes me wonder: would UVIS be capable of picking up a NH3 signature if a suitable stellar occultation pass could be set up right "through" the plumes? What about INMS?


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deglr6328
post Dec 1 2005, 09:14 AM
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There is a second derivative of two ammonia absorption lines which occurs in the near IR at 788nm and is quite strong. VIMS should have ample spectral resolution to pick it out. The line overlaps with a methane overtone at 790nm as seen here in this jupiter spectra but there should be relatively little methane around in this particular observation and if there is any it should be easily constraind by its other strong absorption lines. Also INMS is perfectly suited to detecting this sort of thing if a plume flythrough were to occur.
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edstrick
post Dec 1 2005, 11:28 AM
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Ugordan: "....but haven't there been some mentions recently about ammonia being destroyed by UV sunlight practically immediately so that's one of the reasons it hasn't been detected yet? ..."

I've pointed that out, because NH3 is split by the far more abundant long-wavelength UV than H20, split by much lower intensity short-UV. (In addition, NH3 in an atmosphere like primordial Titan doesn't form the equivalent of an Ozone layer that protects the cold-trapped stuff in the atmosphere below.)

But this pretty much only applies to solid moon surfaces where exposure times are generally *LONG*. Given plausible ice+ammonia compositions for frosts, and the solar spectrum, somebody with the skills and knowledge can (and I'd assume has) published detectability lifetimes for ammonia containing surface frosts in the outer solar system, but I've never seen numbers.

Something like the plumes is entirely different. I can imagine the stuff spread out along the E-ring to have lost NH3 to photolysis, but I can't imagine that stuff in the Enceladus diffuse plume or the narrower jets to be severely ammonia depleted.

I have total confidence that the Cassini mission will try during primary and extended missions to get the best info they can on plume composition and trace vapor/ice limits.
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jmknapp
post Dec 1 2005, 12:23 PM
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QUOTE (BruceMoomaw @ Nov 30 2005, 08:33 PM)
That last quote was actually a misinterpretation by Emily Lakdawalla of what Spilker told her, which is that there was some evidence from particle distribution that the E Ring particles were coming off Enceladus as a whole rather than from the vents.  That particular theory very quickly became inoperative; it's the vents, all right.
*


Seems like you went through this before, and it turns out that Emily Lakdawalla's quote is dead-on accurate & there is little room for misinterpretation--just furious backpedaling.

The article also reports:

"A different in-situ instrument, the Cosmic Dust Analyzer (CDA), had measured Saturn's E Ring particles during previous trips through the ring plane. The vaporous atmosphere detected by UVIS and INMS does not match the particulate nature of the E ring, Spilker said." http://www.planetary.org/news/2005/0730_En...ripes_Spew.html

It doesn't say what those particles are generally--I suppose ice? So I guess the trick is to detect ice particles coming out of the fountains or else figure out how they could form out of the vapor later?


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jmknapp
post Dec 1 2005, 01:08 PM
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Closeups of the tiger stripes are intriguing but a little hard to sort out because of the "crater effect" or whatever it's called where features can seem to flip between convex or concave with each blink of the eye. I think the following (approx. south pole marked with a circle) shows raised ridges on each side of the fissure, as if material has spread out from the fissure?



Knowing that the sun is to the left a bit helps to disambiguate things, based on the shadows.

Another stripe detail:



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dvandorn
post Dec 1 2005, 01:14 PM
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Based on the shadows, the sun is on the *right*... unless you posted the image upside-down to the way you were looking at it when you made the comment.

-the other Doug


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jmknapp
post Dec 1 2005, 01:22 PM
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QUOTE (dvandorn @ Dec 1 2005, 09:14 AM)
Based on the shadows, the sun is on the *right*... unless you posted the image upside-down to the way you were looking at it when you made the comment.

-the other Doug
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I don't think so. Here's an expanded view which shows a bit of the terminator in the lower right. A particuarly long shadow stretching to the right is marked by the arrow:



So the sun would be to the left.


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ugordan
post Dec 1 2005, 02:04 PM
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QUOTE (jmknapp @ Dec 1 2005, 02:22 PM)
So the sun would be to the left.
*

That last image certainly put the things into context, it's really hard to figure out what's high and what's low from small sections of that image you posted. In fact, if the geometry of the image is what I think it is, the sun is precisely on the left hand side, illumination being parallel to the image scanlines.


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dvandorn
post Dec 1 2005, 02:18 PM
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In the context image, your point is clear... but geez, everything that looked like a hole in the original image turns out to be a bump! That's totally counter-intuitive to someone who's been looking at cratered terrains his whole adult life... blink.gif

-the other Doug


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jmknapp
post Dec 1 2005, 02:40 PM
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QUOTE (dvandorn @ Dec 1 2005, 10:18 AM)
In the context image, your point is clear... but geez, everything that looked like a hole in the original image turns out to be a bump!  That's totally counter-intuitive to someone who's been looking at cratered terrains his whole adult life...  blink.gif
*


YMMV, but I find it easier to see correctly if rotated like so:



So the sun is coming in from the top in that view.

It's like ice has flowed from the rift and spread outward, complete with striations going out quite a way, reminiscent of the mid-atlantic ridge perhaps?



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