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Posted by: ugordan Oct 10 2007, 05:20 PM

New press release by the imaging team:

http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=780
October 10, 2007
(Source: Space Science Institute)

CICLOPS link to the release http://ciclops.org/view_event.php?id=70.

One thing I was curious about tiger stripe naming - why didn't they switch "Baghdad" and "Cairo" so we have a nice A,B,C,D progression? I can only imagine it was done on purpose, but why?

Posted by: volcanopele Oct 10 2007, 05:27 PM

Joe Spitale and Carolyn Porco have a paper in Nature, out tomorrow but online today, on the sources of Enceladus' South Polar jets entitled, "Association of the jets of Enceladus with the warmest regions on its south-polar fractures." As you can tell from the title, many of the jet sources are located near hotspots seen by CIRS, and nearly all are located along one of the tiger stripes in the south polar region. For those without access to the article, there is a press release located at http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=780 . In addition, a map showing the hotspot and jet source locations can be found at http://photojournal.jpl.nasa.gov/catalog/PIA08385 . These are really intriguing results, and it would be interesting to see how these sources match up with those of the jets seen a couple of weeks ago. Are the sources variable? Are different parts of the stripes active at different times (as Terry Hurford suggests) or are they more constant and tied to thermal emission sites (as Spitale and Porco suggest)?

Enjoy!

Posted by: belleraphon1 Dec 17 2007, 10:38 PM

All..

I had seen this earlier in the AGU Abtracts but declined to post until we had some fuller reporting.
Unfortunately, this is all that has came forward so far.....


"Sodium issue clouds Enceladus"
http://news.bbc.co.uk/2/hi/science/nature/7145530.stm

quoting from this press release....

"A chemical analysis of Enceladus, led by University of Colorado planetary scientist Nick Schneider, failed to detect sodium, an element scientists say should be in a body of water that has had billions of years of contact with rock.

"If you have a long-lived ocean, it's going to have salt in it," said Dr Schneider, at the American Geophysical Union (AGU) meeting in San Francisco this week, "but that ocean, if it exists on Enceladus, isn't leaking out into space."

"Critics of the study accept his observations, but disagree with his conclusion; and it has led to some robust exchanges here at the AGU meeting this past week. "

March flyby through the plumes is gonna be really interesting....

Craig

Posted by: scalbers Dec 18 2007, 12:10 AM

Interesting to see this sodium discussion continuing. There was also robust discussion after a similar talk by Nick Schneider at the August Outer Planet Satellites workshop.

Posted by: belleraphon1 Dec 18 2007, 01:37 AM

Very interesting indeed.

No Saknussemm Sea? (called this in the movie, not the book.... but it sounds better)
http://www.online-literature.com/verne/journey_center_earth/30/


Cold Faithful - high temperature source for plumes
http://www.planetary.org/news/2007/0322_Chemistry_and_Physics_Suggest_a_Soup.html
http://www.sciencenews.org/articles/20060506/bob9.asp
The process that converts NH3 to N2 and also creates CH4 through serpentization, involves reaction with a silicate core. Hard to see how the salts would be segregated out of the plumes.

Are the salts all in a non-ionized state and invisible? Can INMS detect salts?

Frigid Faithful - low temperature source for plumes
http://www.planetary.org/news/2006/1214_New_Study_Suggests_that_Plumes_on.html
Are the organics at the plume sources captured from other sources in the Saturn system? Or primordial leftovers, not endogenic?

curiouser and curiouser....

Enceladus ain't easy..

Glorious....

Craig

Posted by: DFortes Dec 18 2007, 01:27 PM

http://dx.doi.org/10.1016/j.icarus.2007.06.013

Posted by: belleraphon1 Dec 19 2007, 12:44 AM

Dfortes... Clathrate Faithful? (Although Frigid Faithful also depends on clathrates, I believe)

Very interesting, sir.

I have to assume you are the autthor of this paper?

The paper mentions hydrothermal processing ..... as these xenoliths migrate upwards, would they drag "salts" up with them as well?

As much as I want that ocean to be there, the sodium issue makes me pause. What is really going on here, and what is the plume source? And what powers it?


Craig

Posted by: nprev Dec 19 2007, 12:59 AM

Interesting indeed. Did the Keck observations search for any other elemental signatures other then Na, or was this even practical?

Posted by: DFortes Dec 19 2007, 07:17 AM

Thanks, yeah it's mine. I originally (in a moment of wholly uncharacteristic cynicism) called it tepid faithful. Settled on frothy faithful in the end. The difference with the existing clathrate model is that dissociation occurs in warm rising cryomagma whereas the Kieffer model is entirely dry.

As for the sodium - it is not obvious to me that this rules out the presence of an ocean. I would expect any salts to be carried in aqueous solution and be partitioned into hydrated crystalline phase on eruption, so you would not see the expected spectral signature. In the near IR these hydrated salts will appear similar to ice. Whether or not these salts would become coloured after radiation processing I do not know. Sputtering might yield a small flux of cations - depends on the salt; might be Na, Mg, NH4 etc...

Dom

Posted by: belleraphon1 Dec 19 2007, 01:21 PM

Frothy Faithful... I LIKE that.

Thanks for the clarification between the Frothy and Frigid models, Dom. And your take on the sodium issue. I feel a little more reassured regarding an ocean.

UMSF is greatly enriched by having researchers and mission ops folks among it's members.

Thanks again.

Craig

Posted by: Zvezdichko Feb 8 2008, 07:17 PM

http://saturn.jpl.nasa.gov/news/features/feature20080207.cfm - Enceladus plume model... scientists suggest an underground lake.

Posted by: ustrax Mar 6 2008, 04:27 PM

March 12 flyby description available at http://ciclops.org/view.php?id=4806.

Posted by: scalbers Mar 22 2008, 06:23 PM

Here's a nice powerpoint I came across about Enceladus and its heating - by Tanya Harrison. The pros and cons of the liquid H2O vs clathrate hypotheses are summarized.

http://mgilmore.web.wesleyan.edu/wescourses/2007s/ees471/01/enceladus.ppt

Posted by: MahFL Jun 13 2008, 01:53 PM

From http://ciclops.org/index.php
"And most exciting of all: the highest temperatures now measured are about 180 Kelvins, some 63 degrees Fahrenheit warmer than estimated from previous measurements. Though by no means a guarantee, these results make the possibility of liquid water close to the surface of the moon even more likely. Sacre bleu!..."

Water water everywhere !!!!!

Posted by: tasp Jun 13 2008, 03:26 PM

Maybe . . . .

no, probably not.

Posted by: belleraphon1 Sep 6 2008, 03:13 PM

All... the news above from my post last year has bothered me since I first read it. However in slide 15 of this CASSINI team CHARM presentation, looks like CASSINI has found the sodium....
http://saturn.jpl.nasa.gov/multimedia/products/pdfs/20080826_CHARM_Cuzzi_Seal.pdf

"CDA in situ measurements show water, sodium, silicon in E ring grains, and even some metallic grains which may be on unusual orbits"

Can hardly wait for the team's update on data from the August flyby... and we have two more flyby's coming up next month!!! Wonder if they are hanging onto these results until after those encounters?

Very Cool!!!!

Craig

Posted by: marsbug Sep 11 2008, 11:25 AM

I have a feeling they will wait to release the results, but I hope they don't!

Posted by: Vultur Sep 13 2008, 01:31 AM

I hope not, too. I wonder how many icy moons in the Solar System will turn out to have subsurface oceans - Europa looks very promising, and now Enceladus...

Posted by: dvandorn Sep 13 2008, 02:35 AM

...and according to some sources, Ganymede and even Callisto may have subsurface oceans, albeit not of the extent of Europa's.

-the other Doug

Posted by: ngunn Sep 13 2008, 06:31 PM

Not forgetting Titan, where the solid ice crust has actually been observed floating around a bit relative to the interior - possibly the strongest evidence so far of an internal ocean anywhere. Other possibilities include Neptune's Triton and non-moon Pluto.

Posted by: tedstryk Sep 20 2008, 02:07 AM

Speaking of the jets, check out this night side image - http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details168613.html

Here is a shorter exposure to go with it.... http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=168612

Posted by: vexgizmo Sep 21 2008, 04:37 PM

Maybe middle-sized moons, too, if they contain ammonia which acts like an antifreeze.
http://blog.wired.com/sterling/2008/09/involuted-ocean.html

Posted by: tasp Sep 21 2008, 05:31 PM

Just curious if anyone knows if the R factor of snow increases or decreases if it is in vacuum. If a fluffy surface layer traps heat better than solid ice, and even better if it is vacu-foofed, maybe the internal energy source can be smaller and easier to explain.

Posted by: scalbers Sep 21 2008, 06:58 PM

Quite the images. Interesting that the plumes are visible without a super high phase angle (i.e. a fairly appreciable crescent noted). Comparison to the Saturnshine gives one a nice sense of the plumes' brightness.

Posted by: marsbug Sep 24 2008, 10:16 AM

I know I'm being impatient, and I know that the cassini team have a lot of work to do, but, well I was wondering if it would be worth e-mailing the team and asking if they planned to hold onto the most recent flyby data until after the next two Enceladus flybys. It wouldn't surprise me if they did but, well, I'm just wondering whats happened to it?

Posted by: belleraphon1 Sep 24 2008, 12:54 PM

All..

found the following paper online
"The E-ring in the vicinity of Enceladus II. Probing the moon’s interior—The composition of E-ring particles"

"Abstract
The population of Saturn’s outermost tenuous E-ring is dominated by tiny water ice particles. Active volcanism on the moon Enceladus, embedded in the E-ring, has since late 2005 been known to be a major source of particles replenishing the ring. Therefore particles in the vicinity of Enceladus may provide crucial information about the dynamical and chemical processes occurring below the moon’s icy surface. Here we present a statistical evaluation of more than 2000 impact ionisation mass spectra of Saturn’s E-ring particles, with sizes predominantly below 1 μm, detected by the Cosmic Dust Analyser onboard the Cassini spacecraft. We focus on the identification of non-water features in spectra otherwise dominated by water ice signatures. Here we specify the categorisation of two different spectrum types, which probably represent two particle populations. Type I spectra imply pure water ice particles, whereas in Type II spectra organic compounds and/or silicate minerals are identified as impurities within the icy particles. This finding supports the hypothesis of a dynamic interaction of Enceladus’ rocky core with liquid water."
© 2007 Elsevier Inc. All rights reserved.

http://lasp.colorado.edu/~horanyi/FTP/Cassini_book_chapter/recent_publications/Kempf_E-ring2_2007.pdf

This report details data from the 2005 Enceladus encounters.

From this, the sodium detection appears to be contamination from the detector but the silicate detection is firm.

Enjoy..

Craig

Posted by: marsbug Sep 24 2008, 02:15 PM

They seem to have a good handle on the sodium contamination, would they not take it into account before claiming they had found sodium in the E-ring?

I've decided against badgering the Cassini team (the right and obvious decision but impatience skews my perception sometimes), I'm sure they've got enough on their plates.

Posted by: belleraphon1 Sep 24 2008, 02:37 PM

Keep in mind that this report is from data acquired in 2005. The team may have gotten better data since then.

All be be revealed in due time, I am sure. These teams are no doubt very busy getting together presentations for the upcoming DPS.

Craig

Posted by: Juramike Jun 24 2009, 05:57 PM

New article in Nature according to recent space.com article. Looks like there is evidence for a large body of salty water deep in Enceladus, but that the jets are fueled by slow evaporation deep underground.

The evidence for sodium salts is indirect, coming from E ring dust particles rather than Enceladus jets. (Quoi?)

So more like a humidifier in the corner rather than "Cold Faithful".

Posted by: Ron Hobbs Jun 25 2009, 04:11 AM

In the Geophysical Research Abstracts, Postberg et al. claim to have found Na in the plumes.

http://meetingorganizer.copernicus.org/EGU2009/EGU2009-12013.pdf

This was picked up by the New Scientist, MSNBC and the BBC. (See my posts in the October 31 thread (I don't seem to be able to insert links correctly))

I would love to see a discussion of this finding is relation to the current news.

Posted by: Doc Jun 25 2009, 06:42 PM

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

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

Posted by: john_s Jun 25 2009, 08:30 PM

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 http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=3571 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.

Posted by: nprev Jun 25 2009, 08:38 PM

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?

Posted by: john_s Jun 25 2009, 09:29 PM

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

Posted by: nprev Jun 25 2009, 10:56 PM

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.

Posted by: john_s Jun 26 2009, 06:30 AM

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

Posted by: belleraphon1 Jun 26 2009, 11:31 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.

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

Thanks all!!!

Craig

Posted by: Juramike Jun 27 2009, 01:39 AM

Enceladus Wharrgarbl

Posted by: nprev Jun 27 2009, 01:53 AM

...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...

Posted by: marsbug Jul 1 2009, 12:45 PM

Some http://www.planetary.org/blog/and http://www.agu.org/meetings/ja09/ja09-sessions/ja09_P32A.html

Posted by: marsbug Jul 16 2009, 12:22 PM

http://www.spaceref.com/news/viewpr.html?pid=28739

Posted by: Ron Hobbs Jul 22 2009, 09:08 PM

Ammonia, at last.

http://www.jpl.nasa.gov/news/features.cfm?feature=2238

Posted by: HughFromAlice Jul 23 2009, 09:24 AM

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!!

Posted by: Ron Hobbs Aug 26 2009, 05:29 AM

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.

Posted by: belleraphon1 Aug 26 2009, 12:22 PM

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

Posted by: Ron Hobbs Aug 26 2009, 11:51 PM

I am right there with you, Craig. Actually, I am dreaming of high-tech gondolas carrying tourists among the caverns. Of course, a hydrobot/cryobot would do just fine. If these things do exist, they will be among the most wondrous environments discovered by the scientific imagination.

I wonder if Cassini's radar could try to catch a reflection off the pools?

Posted by: Stu Feb 8 2010, 07:00 PM

Geyser-related story up on the BBC Sci Tech web page today: http://news.bbc.co.uk/1/hi/sci/tech/8495663.stm

Posted by: 2552 Feb 10 2010, 07:54 PM

Another story from space.com: http://www.space.com/scienceastronomy/enceladus-water-100209.html

ADMIN EDIT: Exobiology comments deleted per section 1.3 of the http://www.unmannedspaceflight.com/index.php?act=boardrules. Please take a moment to review them again.

Edit: My apology for not reading the rules the first time, won't happen again.

Posted by: alan Apr 9 2010, 03:18 AM

Pardon the blast from the past. Anyone remember the leopard spots seen along some of the groves imaged during the earlier flybys?

http://www.ciclops.org/view_media.php?id=4783

Could they be related to the jets, perhaps being the sources of jets in the distant past when they emerged from a different part of the moon?

Posted by: volcanopele Apr 9 2010, 05:48 AM

I doubt it. I suspect they are more related to the rough topography, outcrops or boulders, than with cryovolcanism.

Posted by: ugordan Oct 8 2010, 11:04 PM

I suppose this is a good place to post this... I just finished up a color version of http://www.ciclops.org/view.php?id=6232 and it turned out to have two bonuses to it I wasn't aware of. One is that Enceladus' shadow on the E-ring is faintly visible, a rare sight. The second one is the reason why I'm posting this. There's what looks like a dome above the plumes. If you look real closely at the (contrast-enhanced) image below you can pick it up as a discrete change in plume brightness gradient about 1 Enceladus radius above the south pole.

http://www.flickr.com/photos/ugordan/5062968985/

My initial reaction was that this had to be some kind of artifact, but now I'm not so sure. It's visible in at least 3 clear filter frames and a red and blue frame. Moreover, the position of Enceladus was different in the color frames and the feature still follows it, suggesting it's not an optics scattered light effect from Saturn or something (Cassini was in eclipse at that point IIRC, anyway). Here's a natural-ish color R+B image and a heavy unsharp enhancement.

It looks like a bow shock in the plume but my gut says the whole thing is too diffuse for that. What do you think? Artifact or real?

Posted by: nprev Oct 8 2010, 11:23 PM

Hmm. Subtle, good catch!

To me, the 'dome' looks like it's produced by plume particles that are in the foreground of the general E-ring glow. In other words, I see Enceladus's circular black shadow on the E-ring in the background, and it looks like this is a perspective effect. Is there any way to make a stereo pair? That might be a good test of this idea.

Posted by: alan Oct 8 2010, 11:42 PM

The dome appears to continue through the shadow and may wrap all the way around, perhaps its an optical effect of the e-ring related to the lighting

Below is your image with the histogram equalized.

Posted by: ugordan Oct 9 2010, 12:15 AM

I can't see how it would be a lighting effect on the ring unless the sun happened to be precisely behind Enceladus. The phase angle was high, 174 degrees, but even that is still 17 NAC FOVs away from the sun!

It does seem to fit inside Enceladus' Hill sphere and is elongated in the N-S direction, though.

Posted by: alan Oct 9 2010, 12:55 AM

Yea, thought about that after I hit post.

Posted by: nprev Oct 9 2010, 01:23 AM

Ahh...my bad, Gordan, misinterpreted what you meant by 'dome'. Just to be sure I'm on the same page now, would characterize what I think you mean as a halo or even aureole that completely encircles the moon(?)

EDIT: Wow. Does indeed look like there's an enrichment of material in what appears to be Enceladus' Hill sphere. The N/S elongation might be due to the effects of Saturn's magnetic field on what (I guess) highly diffused water vapor mixed with OH & H3O radicals. Again, wow!!!

Posted by: remcook Oct 9 2010, 09:42 AM

Yet another great spot, Gordan! And a beautiful image!

Elliptical halo caused by scattering by the ring particles of light coming from Enceladus? http://www.atoptics.co.uk/fz409.htm
Whatever it is, it's pretty cool.

Posted by: ugordan Oct 9 2010, 09:43 AM

I wonder if it's merely the effect of particles being more stably bound to Enceladus in those directions than in the orbital plane. If it's linked to the Hill sphere at all, that is.

Posted by: ugordan Oct 9 2010, 09:46 AM

The problem with that is that this halo would be very very small. Remember the narrow-angle camera has a FOV of 0.35 so any ice halos we're familiar with here on Earth couldn't possibly completely fit into the frame. Not even in the wide angle camera.

I'll have to check if anything of the sort is visible in earlier observations, although they were nowhere as close to such a high phase angle.

Posted by: remcook Oct 9 2010, 10:08 AM

Yeah, I don't know what angles these inner rings of these halos go to.

About the Hill sphere thing: would you expect the most material to be at the outer edge?

Posted by: ugordan Oct 9 2010, 10:20 AM

I don't know what I'd expect! That doesn't appear to be the case, though. Look at alan's enhancement. It appears to be more or less uniformly "filled".

Posted by: remcook Oct 9 2010, 10:25 AM

I see a little bit of a ring, but indeed small contrast. Might be optical illusion. But very sharp boundary indeed. It's just weird

Posted by: ugordan Oct 9 2010, 11:32 AM

Perhaps the most compelling evidence that this is not an optical artifact or optical effect in the ring particles comes from comparing two frames taken at different distances.
Below's a comparison of two clear filter frames taken from 617 000 km and 540 000 km, that's a 14% difference in distance. First, both images at their original pixel scales:

http://i108.photobucket.com/albums/n15/ugordan/enc_egg.gif

And here's the match when resized to the same pixel scale:

http://i108.photobucket.com/albums/n15/ugordan/enc_egg_resized.gif

The overall E-ring brightness drops off rapidly with lowering phase angle so it's not really surprising this can only be seen in the highest phase angle imagery Cassini has obtained so far (notwithstanding the grand Saturn eclipse sequence as that was too low resolution).

Posted by: ZLD Oct 9 2010, 06:29 PM

I've just finished looking through tons of other sets of pictures that feature Enceladus and am missing any good signs of the halo around the planet in past pictures. This isn't to say that it isn't still there; it may need to be lit in a very particular angle for the diffusion of the particles to reflect it in the lens. A more interesting possibility could be that this is something that has just been generated or at least become more prominent due to the changing season.

In this image from Rev 121, only a very faint presence of this halo exists. I would be inclined to say that this is more likely an optical illusion or a processing artifact but after overlaying the other processed image on top, they clearly line up. Take that however you will.
http://imgur.com/owRvM.pnghttp://imgur.com/oUCS6.png

-Edit: I Just realized I hadn't rotated the image in that overlapping example. Here is the corrected image (though only a very quick aligning was done). Interestingly, they still appear to line up.
http://imgur.com/Wwc0Z.png



I did however stumble onto something else interesting in looking through past photos. PIA_12693 from early in August, it looks like there is a somewhat prominent blurring/diffusing circling the moon. I've blown up the image 400% to show this more clearly. Not sure if this illustrates anything really but the diffusing effect is quite similar to the one of the much larger halo.
http://imgur.com/fh5VD.pnghttp://imgur.com/VhQzR.png


Strange and interesting indeed.

-Zac

Posted by: nprev Oct 9 2010, 06:45 PM

Just a thought here: Maybe the halo boundary is actually at Enceladus' Roche limit distance (liquid satellite version), which is pretty small (smaller than the putative Hill sphere radius, presumably.)

EDIT: This seems to make sense. The stuff in the halo is actually in orbit around Enceladus; beyond the critical radius it goes into orbit around Saturn. The N-S elongation is caused by excess velocity imparted to some of this stuff from the south polar plumes, which is pushing some of the material into polar elliptical orbit; presumably a lot of this gets picked off by Saturn as well & joins the E-ring.

Posted by: ZLD Oct 9 2010, 06:57 PM

The only problem that I see with the halo is that basically what you're describing is an atmosphere and as I understand it, moons as small as Enceladus, which is quite small compared to even our own moon, aren't supposed to be able to retain particles of this size. If the halo was made up of semi-large icy chunks, I could see it being more possible but then it should also be much more visible. The distance the halo extends away from the surface is also baffling considering the size of Enceladus. More data is necessary.

Posted by: ugordan Oct 9 2010, 07:09 PM

Not an atmosphere, atmospheres aren't in orbit around the parent body. These particles (not gas) *might* be in orbit around Enceladus.

FWIW, I looked at previous high phase imagery and have not seen anything of the sort. Even a wide-angle context frame taken at roughly the same time doesn't show it, though the low resolution and graininess leaves something to be desired.

Posted by: brellis Oct 10 2010, 05:49 AM

Oxygen ends up in Titan's atmosphere. Might that be related?

Posted by: nprev Oct 10 2010, 05:59 AM

Maybe. Enceladus' emissions seem to end up splattered all over the Saturnian system; the E-ring is just the densest part of it.

Posted by: brellis Oct 10 2010, 06:09 AM

Got it! A halo would imply a wide emission of material. Perhaps at certain points it emits more stuff towards Titan, other times it feeds the E-ring, and other times it recollects material?

re ZLD's post: Perhaps it is a trailing atmopshere, almost like a comet?

Posted by: ZLD Oct 10 2010, 08:17 AM

A trailing atmosphere, similar to a tail and coma on a comet, could be a possibility but generally for those to be present even around a comet, they have to be rather close to the sun before they are present. The lack of any type of obvious tail also presents a problem with that theory. However, the data is obviously inconclusive and pretty much anything is open for possibility at the moment as this seems to be something entirely new to everyone.

-Zac

Posted by: nprev Oct 10 2010, 08:55 AM

Let's step back a bit & look at the situation:

1. Enceladus is a teeny little mass very close to a very large mass.

2. Enceladus is active, and emits a steady stream of (mostly) water vapor continuously into space.

I don't think that the comet analogy really applies here. Comets are much smaller than Enceladus, and as ZLD points out their emissions are a consequence solely of solar effects on their substance. They have effectively no gravitational influence over their surroundings, so their emissions just blast off into space more or less in the same direction as the stimulating radiation.

In contrast, Enceladus is massive enough to hold onto at least some of the stuff it's venting. Also, Saturn's gravitational influence is much more influential than solar radiation pressure, esp. at the system's distance from the Sun.

So, what I think might be happening here is as follows:

1. Enceladus is surrounded by a spheroid of emission products from the south polar jets; this is Gordan's halo, and it's caused by particles in orbit around the moon that didn't achieve escape velocity.

2. The polar elongation of this spheroid is due to either magnetic effects from Saturn or the fact that some of the particles blasted out by the jets are more energetic than others & end up in elongated polar orbits, or both. (The fact that the elongation is N-S really leads me to think that the polar-orbit effect is real & dominant, and mostly an artifact of the location of th jets on the moon.)

3. Eventually, the stuff in the halo escapes (possibly aided by solar radiation pressure and/or other electromagnetic effects from Saturn), but it can't get out of Saturn's Hill sphere so it becomes the E-ring & a much more diffuse & extended torus of material that encompasses pretty much all of the inner moons out to Titan. (Titan itself probably bounds it rather effectively by sweeping up damn near all of the material before it can migrate outward any further from Saturn).


Anyhow, that's my theory. Reality of course may be completely different!

Posted by: remcook Oct 11 2010, 12:51 PM

So, it does seem to be something physical, not optical. From a gut feeling sort of thing, I would expect stuff that would hang around Enceladus to be more dense near the moon itself and not be so neatly uniformly distributed with such a sharp edge. Some (dynamical) simulations people have done for Enceladus (for those with access :S ) seem to show something similar :
http://www.scienceonline.org/cgi/reprint/311/5766/1416.pdf
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4XG3SFK-1&_user=3021449&_coverDate=04%2F30%2F2010&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1493142743&_rerunOrigin=google&_acct=C000021878&_version=1&_urlVersion=0&_userid=3021449&md5=8ce7825bd038c9b254c81c314fd4a4a3&searchtype=a

http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2635.pdf (free)

So, something else might be going on as well? weirdness stays

Posted by: ugordan Oct 11 2010, 01:27 PM

On the other hand, there's a problem with this conclusion. I would expect Cassini's sensitive fields and particles instruments to pick up this change in perceived optical density as well if it was an actual density gradient. Also, wouldn't UVIS occultations pick up this enrichment in material - although it's possible measurements typically started closer in than about 2 Enceladus radii?

Posted by: remcook Oct 11 2010, 02:54 PM

Indeed. Personally, I'm not convinced by any possible explanation at the moment.