[X] My Assistant

[alan]

Six days to go until Enceladus flyby ( E2? ) at 175 km

[Decepticon]

We also get NT encounters. I hope we get those images also.

[volcanopele]

I should be posting my E2 preview either today (maybe...) or early next week on my blog.

[volcanopele]

That E2 preview is now online:
http://volcanopele.blogspot.com/2005/07/en...her-rev-11.html

[volcanopele]

21000 km to Enceladus

Can't wait to see the images tomorrow

[DEChengst]

Can't wait to see the images tomorrow

Yep I have my panorama software ready and waiting

Let's hope that the rawimages website won't suffer from the Red Cross Disease again

[scalbers]

Should be neat to see the images. I have been watching using Celestia to visualize the view of Enceladus from Cassini's vantage point. It is running with a real-time animation using a version of my Enceladus map.

[Decepticon]

I don't expect anything till monday. When an encouter falls so close to the weekend we get plauged by the red x problem.

[Phillip]

Update on the Cassini website:

Enceladus Flyby Update
The Cassini spacecraft conducted its closest flyby yet, coming within 175 kilometers (109 miles) from the surface of Enceladus. Data collected is currently being downloaded. Raw images are expected to appear on this web site at around 10 p.m. PDT.


http://saturn.jpl.nasa.gov/home/index.cfm

[volcanopele]

http://ciclops.org/view_event.php?id=22

[alan]

From 545 kilometers

[volcanopele]

actually, that's distance to target center so the altitude is actually 295 km

2 m/pixel

[exoplanet]

http://ciclops.org/view_event.php?id=22

WOW!!! Why are the boulders so rounded and what are those dark holes!!!

[dvandorn]

Is that Enceladus or a block of London flats after The Blitz?

Fascinating right angles, there...

-the other Doug

[imran]

Is that Enceladus or a block of London flats after The Blitz?

Fascinating right angles, there...

-the other Doug

Wow. This terrain looks strikingly similar to Europa.

[DEChengst]

First mosaic of this fly-by. Looks like it was take in Saturn shine:

http://paranoid.dechengst.nl/saturn/Enceladus5.jpg

[Gsnorgathon]

Nice distant view of the tiger scratches (or whatever they're called).

[DEChengst]

Six frame highres mosaic. Some artifacts due to the changing viewing geometry between frames though

http://paranoid.dechengst.nl/saturn/Enceladus6.jpg

Three frame mosaic. Couldn't get the bottom left quadrant to fit properly

http://paranoid.dechengst.nl/saturn/Enceladus7.jpg

[edstrick]

DEChengst: I can't get any of your links tonight to load, either viewing them directly, or using the 'Save As' trick. "The page you are looking for is currently unavailable" message.

Note... that Super-High-Rez image is motion blurred. Nice linear blur. Should be easy to deconvolve to nearly full resolution.

[Bill Harris]

Wonderful images!

Ed, I was able to download DEChengst's images at 6:30AM CDT, FWIW.

--Bill

[Decepticon]

Am I seeing things?


The Tiger scratches seem to have something coming out of them!?

Like a haze. It could be along the sides of the 3 cracks possible on the ground.

This is speculation on my part.

[tedstryk]

Here is another version of the crescent mosaic...I processed it to hide the saturn-shine areas so that you can't see the missing areas.

[Guest_Myran_*]

Deception said Am I seeing things?

Also I can see that the 'Tiger scratches' are somewhat darker, yet I interpret that somewhat differently. Imagine you have a snow like material or ice grinded into small pebbles by meteorites etc covering most of the surface. Any upwelling from below, be it a billion years ago or perhaps more recent would quickly freeze and create darker ice near the cracks. So thats what I think we see, cracks with a lining of clearer material therefore darker ice.

[TheChemist]

Here is where the closeup image N00037070.jpg fits in the larger one (W00009337.jpg)
Dead on the center

Attached thumbnail(s)

 

[remcook]

Wow, especially the tiger scratches look amazing!!

[Rob Pinnegar]

Hey... check out that diamond shaped region to the upper right of the "tiger scratches" in the above referenced image. Anyone remember Miranda's "chevron" feature?...

[tty]

Very strange morphology. Some of the larger "scratches" seem to show evidence of parts of the wall sliding into the valleys. Also notice how some craters show radial cracks in addidion to the main crack pattern and the virtual absence of impact craters in the lower part of the mosaic. This is fairly young terrain.

tty

[alan]

I was surprised to the the boulders is closest image. I don't remember seeing boulders in the closeups of Europa

[Roby72]

I refer to the high res image of Enceladus. I suspect a pixel size of about 6-7 meters because the distance is 545km acc. RAW data and 2x2 binning of the sensor. These boulders must be really large ones !
IMHO the larger distance results from the other black images, that shows smaller distances than Enceldaus radius (for example W00009338.jpg in 210 km distance).
Further it could be still larger away because of the oblique angle of this particular shot.

Robert Schulz

[dvandorn]

Obviously, remnants of surficial cracking from either gravitic stresses on Enceladus or from internal stresses which caused upwelling from the cracks.

Europa, anyone? This looks like extensive cracking atop a liquid ocean...

-the other Doug

[Tman]

Here is where the closeup image N00037070.jpg fits in the larger one (W00009337.jpg)
Dead on the center 

Thanks for answer the puzzle
Made with it a little GIF animation: http://www.greuti.ch/cassini/enceladus_closest.gif

[Decepticon]

Double post.

[Decepticon]

Nice work!

[Decepticon]

My attempt at a colored image. Note I'm new at this!
DEChengst I hope you don't mind me using your stitched image (One of my favs )

[DEChengst]

DEChengst I hope you don't mind me using you stitched image.

Sure I don't mind. Anyone can use or publish my images as long as it comes with the words "stitched by DEChengst"

[tty]

Wow.  This terrain looks strikingly similar to Europa.

I don't think so, this looks more like some kind of icy version of plate tectonics than an ice-covered world ocean.

tty

[volcanopele]

I don't think so, this looks more like some kind of icy version of plate tectonics than an ice-covered world ocean.

tty

I'm going to cover this in a blog post later today, but I agree with you, at least in that I don't think there is an ocean. A lot of people are focusing on the similarties between Enceladus and Europa, but they seem to ignore the major differences. Europa's surface age is the same to within an order of magnitude through the surface, whereas there are significant differences in surface age (or at least crater retention age) between various regions on Enceladus. You have a nearly crater free south polar region, while the north polar region appears to be very heavily cratered. This dichonomy is more reminiscent of Miranda than Europa. so I suspect that the current diapir theory for corona formation on Miranda might work for planitia formation on Enceladus, with some modifications.

[imran]

I don't think so, this looks more like some kind of icy version of plate tectonics than an ice-covered world ocean.

tty

I agree with you to some extent. The second image on volcanopele's site was what I was referring to when I made that comment. Unlike Europa, the surface of Enceladus is more diverse and the age of the surface varies with different regions. And I agree with volcanopele in the sense that the likelihood of there being an ocean is much lower than on Europa.

[Guest_BruceMoomaw_*]

I think there's something more dramatic going on at Enceladus than at Miranda. First, we have the multiple evidence for outgassing, which indicates current activity. Then, we have the extreme youth of some of the tectonic features -- just look, for instance at http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=45673 .

I think that what we're seeing at Enceladus -- just as it's believed we're seeing it at the inner three Galilean satellites -- is INTERMITTENT tidally stimulated geological activity over cycles of tens to hundreds of millions of years, produced by the fact that the moons keep drifting into and out of more or less intense resonance relationships as they slowly spiral away from their central planets. In the case of Enceladus, the cycles are a lot slower and less intense than with Europa -- a matter of 100 or 200 million years, rather than just a few tens of millions, and not intense or widespread enough to obliterate most of the moon's craters -- but they are nevertheless there. I suspect Enceladus' remaining outgassing is a result of the fact that it's still cooling off from its last period of maximum tidal heating. But I also wouldn't be surprised if, even at its maximum, Enceladus' geological activity didn't take the form of oozing warm-ice diapirs with only a relatively small amount of liquid water/ammonia mixed in, just as Jason suggests.

Having said that, let me add that the geology of the Uranian satellites is one of my biggest remaining areas of ignorance about the Solar System -- I just haven't quite gotten round to studying them yet, for some reason.

[edstrick]

Looking at the raw images of the south polar region on Enceladus, I don't see *** ANY *** impact craters in large swaths of the swirly-ridge-and-trough terrains. This surface is young. Damn young. ?tens? of millions of years max, maybe.

[Bill Harris]

Then, we have the extreme youth of some of the tectonic features -- just look, for instance at http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=45673

And at the contact between the two terrains at the bottom 1/4 of the image, there is a line of boulders.

Odd place, this...

--Bill

[tedstryk]

A nice little shot of Pandora over the clouds of Saturn has come in!

[alan]

That was quick: updated map of Enceladus on Steve Albers website
http://laps.fsl.noaa.gov/albers/sos/sos.html

[Decepticon]

Does steve have polar projections?

[Phil Stooke]

I shamelessly stole Steve Albers' cylindrical projection of Enceladus (thanks!) and made this polar projection of the southern hemisphere (just using the polar coordinates function in Photoshop):




Incidentally, the saturnshine images from the last imaging sequence on this orbit show new territory west of Voyager 2 coverage which could be added in to the northern hemisphere of the map.


Phil

[Decepticon]

Very nice.

I wonder how enceladus magnetic field/south pole lines up with those "4 cat scratches"

[Decepticon]

Another attempt at a coloring.


I'm not sure how this is done correctly.
Is there a site that explains how to this in adobe?

[tedstryk]

I think that we got some pretty good coverage of the North Polar region on the leading hemisphere from Saturnshine images. As for the other side, the highest resolution Voyager set covers much of it. I am working on a super-res image.

[pioneer]

I don't know about anyone else, but I haven't found any signs of ice volcanoes or guysers yet.

[scalbers]

I shamelessly stole Steve Albers' cylindrical projection of Enceladus (thanks!) and made this polar projection of the southern hemisphere (just using the polar coordinates function in Photoshop):




Incidentally, the saturnshine images from the last imaging sequence on this orbit show new territory west of Voyager 2 coverage which could be added in to the northern hemisphere of the map.
Phil

Phil,

Thanks for the polar view - interesting to see it all laid out. I'll probably be working on adding one or more additional sunlit images from this flyby, particularly at high southerly latitudes. After that I can see what would be involved in some of the Saturnshine images.

[tedstryk]

Here is all I could do...the images are at impossibly different angles.

[alan]

Bizarre boulders litter Saturn moon's icy surface

On 14 July, Cassini swooped in for an unprecedented close-up view of the wrinkled moon. Its Imaging Science Subsystem (ISS) camera has since returned pictures of a boulder-strewn landscape that is currently beyond explanation. The "boulders" appear to range between 10 and 20 metres in diameter in the highest-resolution images, which can resolve features just 4 m across.
“That’s a surface texture I have never seen anywhere else in the solar system,” says David Rothery, a planetary geologist at the Open University in Milton Keynes, UK.
Cracks crisscross Enceladus's surface - possibly as a result of the moon being repeatedly squeezed and stretched by the gravity of Saturn and other moons nearby. But Rothery points out the boulders avoid - rather than fill - the cracks. This might indicate that the fracturing took place after the boulders had already formed.
Alien landscape
John Spencer, a Cassini team member at the Southwest Research Institute in Boulder, Colorado, US, agrees that the images are puzzling. “You would expect to see small craters or a smooth, snow-covered landscape at this resolution," he told New Scientist. "This is just strange. In fact, I have a really hard time understanding what I’m seeing.”

http://www.newscientistspace.com/article.ns?id=dn7692

I wonder what happens when a mixture of water and ammonia freezes. Would some of the water freeze first, forming ice boulders, leaving a more concentrated mixture of water and ammonia behind? If a mix of icy boulders and liquid water-ammonia reached the surface, the liquid at the top could vaporize leaving the boulders behind.

[edstrick]

Post-Voyager, there was a spate of studying the potential of ammonia/water volcanism. Assorted studies of the very complex phase diagram of the two ices and the physical properties of melts. Some melts at low temperatures are very runny-liquid, while higher temperature melts with a different ammonia/water molecular ratio is like soft-taffy! Certainly there were a number of abstracts in the yellow-books: LPSC conference Abstracts from the period. Where final papers were published, I don't know.

Note that it's unlikely ammonia will be dectected on Enceladus's surface even if eruption is happening recently in geologic terms.. It takes hard UV to split oxygen and hydrogen. Quite soft UV, of which sunlight has a lot more, is all you need to split nitrogen and hydrogen. Exposed ammonia ice will have a quite short <years? decades?> lifetime.

[Roby72]

Any news about the INMS and UVIS observations ?

[Gsnorgathon]

...
Exposed ammonia ice will have a quite short <years?  decades?> lifetime.
...

I've seen the expected lifetime of methane in the martian atmosphere mentioned all over the place, but never the expected lifetime of exposed ammonia on any out solar system body.

[Guest_Myran_*]

Gsnorgathon said: I've seen the expected lifetime of methane in the martian atmosphere mentioned all over the place, but never the expected lifetime of exposed ammonia on any out solar system body.

Not me either, but I do remember from one article that the author expected that the ultraviolet radiation from the sun would have broken down ammonia on the surface of Saturn's smaller moons over time.

But again Pluto's moon Charon is thought to have ammonia ices,
Evidence for Crystalline Water and Ammonia Ices on Pluto's Satellite Charon

Even without more exact numbers I can still say to edstrick&Gsnorgathon that it would be far longer than years or decades, rather millennia to millions of years.

[Decepticon]

New update.


http://ciclops.org/view_event.php?id=23

[dilo]

New update.
http://ciclops.org/view_event.php?id=23

Yes, absolutely magnificent images, but very slow link in this moment (too traffic, maybe)
I enhanced colors here, pretty nice and interesting:

[volcanopele]

The magnetometer instrument confirmed an atmosphere at Enceladus during the July 14 flyby. Data from this flyby and modeling work of previous data shows that the atmosphere is concentrated over the south polar region and is much more rarified over the rest of the surface.

The plot thickens...

http://www.pparc.ac.uk/Nw/enceladus_flyby.asp

http://volcanopele.blogspot.com/2005/07/pr...instrument.html

[volcanopele]

UVIS detects Enceladus' atmosphere (and also sees the same spatial non-uniformity that MAG found):

http://photojournal.jpl.nasa.gov/catalog/PIA06431

And now for the punch-line: CIRS found a hot spot near Enceladus' south pole:

http://photojournal.jpl.nasa.gov/catalog/PIA06432

[remcook]

news release:

http://saturn.jpl.nasa.gov/news/press-rele....cfm?newsID=592

very interesting indeed! Looks more and more like Europa, only active!

[dilo]

The magnetometer instrument confirmed an atmosphere at Enceladus during the July 14 flyby.  Data from this flyby and modeling work of previous data shows that the atmosphere is concentrated over the south polar region and is much more rarified over the rest of the surface.

http://www.unmannedspaceflight.com/index.p...ype=post&id=339
...something like this, Jason?
See http://www.unmannedspaceflight.com/index.p...findpost&p=5657

[volcanopele]

Sorry for the double post, didn't realize I was posting in the wrong thread:

nope, still an image artifact. If it were real, then when viewed from the same geometry, here are plumes over Mimas, Rhea, Tethys, and Titan over the same area of the crescent.

However, I can't deny we haven't gone back and taken another look at it. but mostly likely the activity we are seeing is do to evaporation or outgassing rather than a full fledged plume.

[David]

And now for the punch-line: CIRS found a hot spot near Enceladus' south pole:

http://photojournal.jpl.nasa.gov/catalog/PIA06432

Fantastic stuff! Too bad it's still 150 below freezing. I wonder how much hotter it might get inside Enceladus?

[Decepticon]

Enceladus looks more like Ganymede instead of Europa.

[scalbers]

How neat that this is the punchline to the evidence building up over months and even decades. Perhaps 6-12 months ago, the Y shaped features looked at low resolution like some sort of amorphous petals of a giant flower ringing the south pole. Even then something strange was being foreshadowed and how fun it has been to see the resolution gradually increase since then.

Yesterday (July 29) there was a CICLOPS release of the tiger scratches in enhanced color close up. Overlain are 10 squares showing the CIRS temperature measurement pixels. It actually can pinpoint the tiger scratches as the heat source.

[dilo]

Sorry for my insistence, Jason. Can you kindly pinpoint an image showing similar artifact on Mimas, Rhea, Tethys, and Titan? thkx

[JRehling]

And now for the punch-line: CIRS found a hot spot near Enceladus' south pole:

http://photojournal.jpl.nasa.gov/catalog/PIA06432

I'll point out: Those nifty temperature profiles across a tiger scratch showing higher temps in the scratch area are of pretty low resolution, so their reading of a higher temperature may be quantitatively averaging "normal" surface units with a smaller, very-warm lineated feature. The actual high temperature -- who knows? Something near 0C would be exciting. I don't know if the remaining Enceladus flyby of the regular mission will inspect this or not -- given the geometry, I give it an odds-on "I doubt it".

Next we have to see if the north pole area also has a warm spot of any kind.

[DEChengst]

I'll point out: Those nifty temperature profiles across a tiger scratch showing higher temps in the scratch area are of pretty low resolution, so their reading of a higher temperature may be quantitatively averaging "normal" surface units with a smaller, very-warm lineated feature. The actual high temperature -- who knows? Something near 0C would be exciting.

Even a much lower temperature can be exciting. An ammonia-water eutectic mixture is liquid at 176 Kelvin, so there might very well be active cryo volcanos on Enceladus.

[tty]

I wonder could those "tiger scratches" be something analogous to mid-ocean ridges where "lava" from below intrudes and pushes "lithospheric" plates apart?

tty

[volcanopele]

Sorry for my insistence, Jason. Can you kindly pinpoint an image showing similar artifact on Mimas, Rhea, Tethys, and Titan? thkx

I'll have to check with the person who did the analysis on the problem.

[volcanopele]

I'll point out: Those nifty temperature profiles across a tiger scratch showing higher temps in the scratch area are of pretty low resolution, so their reading of a higher temperature may be quantitatively averaging "normal" surface units with a smaller, very-warm lineated feature. The actual high temperature -- who knows? Something near 0C would be exciting. I don't know if the remaining Enceladus flyby of the regular mission will inspect this or not -- given the geometry, I give it an odds-on "I doubt it".

Next we have to see if the north pole area also has a warm spot of any kind.

As DEChengst pointed out, you don't need 0C for liquid water thanks to ammonia, assuming it is there. In terms of pixels, the CIRS team determined that in the 91K box, color temperatures are consistent with a background temperature of 85K or so, with 1% at 140 K. 1% of a 6x6 km box is .36 km2, consistent with a box-shaped area of about 19.5x19.5 m.

The other thing I was going to say, the north polar region is deader than a doornail (or Mimas, same thing). 38K or so.

[tedstryk]

The other thing I was going to say, the north polar region is deader than a doornail (or Mimas, same thing).  38K or so.

Hardly suprising....it looks old and battered. I have marked it here with an arrow.

[tty]

As DEChengst pointed out, you don't need 0C for liquid water thanks to ammonia, assuming it is there.  In terms of pixels, the CIRS team determined that in the 91K box, color temperatures are consistent with a background temperature of 85K or so, with 1% at 140 K.  1% of a 6x6 km box is .36 km2, consistent with a box-shaped area of about 19.5x19.5 m.

Actually 0.36 km2 is 600 x 600 meters, or since we are talking about linear features 6000 x 60 meters.

tty

[volcanopele]

grrr....true, very true. It was a Sunday morning..I'm never awake on a sunday morning.

[tedstryk]

This might be a better example than just pointing out the poles....a side by side comparison of the terrain around each polar region.

[scalbers]

Greetings,

Thought I'd mention some speculations about a couple of items in this topic. I wonder if it would be that surprising to be able to obtain enough tidal heat to warm Enceladus? Note its orbital eccentricity of .004 and the significant tidal distortion of its equatorial radius in the X and Y directions (5-10km?). A rough guestimate of the tidal flexing within each orbit might then be 10-20m? Would this be of the same order of magnitude as the tidal flexing on Europa? On the other hand, this line of reasoning would suggest much more tidal heating of Mimas, having a more elliptical shape and greater orbital eccentricity.

Will be interesting to hear more of VP's investigation of the glare/artifact that looks like a plume. My speculation is that it would not be caused by the sun if it is well correlated by Enceladus' position. Also, given that it appears to emanate from the S polar region and not other portions of the crescent, it's difficult for me to imagine a type of glare pattern that would do this, since the crescent should have relatively uniform illumination over its area.

[volcanopele]

Will be interesting to hear more of VP's investigation of the glare/artifact that looks like a plume. My speculation is that it would not be caused by the sun if it is well correlated by Enceladus' position. Also, given that it appears to emanate from the S polar region and not other portions of the crescent, it's difficult for me to imagine a type of glare pattern that would do this, since the crescent should have relatively uniform illumination over its area.

It is not my investigation at all. But from my understanding this caused by a camera artifact, essentially a scattered light issue. This problem is very apparent on images of targets that are: overexposed and high phase. One possible example with Saturn is here:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=46019

In terms of heating, don't forget the evidence that Enceladus' orbit has migrated back and forth, interestingly across the Dione 2:1 resonance.

Artifact seen in:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=29948 [Enceladus, same position on crescent, not on surface, weaker since not overexposed)

[Gsnorgathon]

That's an interesting tidbit about Enceladus wandering back and forth through the Dione 2:1 resonance. I hadn't heard that. Do you have a link handy?

[volcanopele]

That's an interesting tidbit about Enceladus wandering back and forth through the Dione 2:1 resonance. I hadn't heard that. Do you have a link handy?

Enceladus is currently in a 2:1 resonance with Dione and the crinkled terrain along the edges of south polar terrain suggest that Enceladus' shape has changed over time, from despinning and upspinning. Such shape and spin rate changes are most likely the result of Enceladus' orbit changing, likely hovering aroung the 2:1 resonance.

[john_s]

I don't know if the remaining Enceladus flyby of the regular mission will inspect this or not -- given the geometry, I give it an odds-on "I doubt it".

Next we have to see if the north pole area also has a warm spot of any kind.

Actually, we are very lucky with the remaining Enceladus flyby on Rev. 61- we fly in over the north pole and out over the south pole, so we'll get a great look at the south pole. What's especially handy for those of us on the CIRS teams is that Enceladus enters Saturn eclipse right around closest approach, so the ISS VIMS and UVIS teams won't be able to do very much and we'll get most of the observing time. We'll certainly be revising our observing plans based on the new discoveries.

[Guest_BruceMoomaw_*]

Well, that means YOU'RE very lucky, but the same can't be said for scientific observations of Enceladus as a whole during the next flyby. Once again, several more flybys are obviously needed during the extended mission.

[john_s]

Well, that means YOU'RE very lucky, but the same can't be said for scientific observations of Enceladus as a whole during the next flyby.  Once again, several more flybys are obviously needed during the extended mission.

True enough- we are the beneficiaries of what's an unfortunate circumstance for the overly flyby science. The fact that Enceladus was going to be entering eclipse near closest approach was only discovered after this flyby had already been scheduled. The other remote sensing instruments will get great data on the north pole on approach, but of course that's not where the action is. We all hope there will be additional Enceladus flybys in the extended mission, and these new discoveries will make that a high priority.

[scalbers]

I shamelessly stole Steve Albers' cylindrical projection of Enceladus (thanks!) and made this polar projection of the southern hemisphere (just using the polar coordinates function in Photoshop):




Incidentally, the saturnshine images from the last imaging sequence on this orbit show new territory west of Voyager 2 coverage which could be added in to the northern hemisphere of the map.
Phil

Thought I'd mention that I've updated my Enceladus map again today, now having several more of the detailed south polar images.

[Gsnorgathon]

Don't be so shy, Steve! Put in the link!

[Guest_BruceMoomaw_*]

I talked this afternoon with Dr. Linda Spilker -- and it turns out that the puzzle
of that quote from her in the Planetary Society article (
http://www.planetary.org/news/2005/encelad...ctive_0730.html )...

"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."

...is explained by the simple fact that Emily Lacdawalla misquoted her, and
in fact apparently made the last sentence up out of thin air. (Upon being
informed of what she was being quoted as saying, Spilker promised to give
Emily a Talking To.) So here's the real story:

What she actually told Lackdawalla is that the E Ring particles, as analyzed by Cassini's Cosmic Dust Analyzer, are basically just water ice, while the stuff that Cassini detected at Enceladus' south pole is water VAPOR. Period. End of story. No meaningful compositional difference to indicate that the E Ring particles are not coming originally from Enceladus' southern vents -- in fact, she agreed that it's very hard to explain the E Ring particles as having been knocked off Enceladus by meteoroid impacts, for the simple reason that in that case we'd see comparable rings centered around the orbits of Saturn's other icy moons.

When I suggested the following model of what is actually going on, she also
agreed with it: Water/ammonia mixture, with a little methane mixed into it (as also detected by Cassini), is spurting from vents near Enceladus' south pole -- indeed, the vaporizing methane is probably largely responsible for driving the venting. (The vents are probably those little dark speckles, near the cracks, that look like Enceladan blackheads -- at any rate, http://www.aas.org/publications/baas/v37n3/dps2005/450.htm says so.
Presumably their blackness results from the fact that a small amount of the
methane has been locally radiolyzed into dark carbon compounds, just as on
Pluto.)

The NH3 vapor is almost immediately broken down by solar UV into nitrogen
and hydrogen, thus explaining both the lack of NH3 in Cassini's gas analyses
and the surprisingly large amount of molecular hydrogen in it. This also
means that most of the 28 AMU gas detected by Cassini is indeed nitrogen
rather than carbon monoxide. (It turns out that Cassini's UVIS can measure both
CO and atomic N --http://www.aas.org/publications/baas/v37n3/dps2005/452.htm -- but, like a
fool, I forgot to ask Spilker about its findings. However, we already know
that most of the atomic N in Saturn's magnetosphere is concentrated around the E
Ring, with very little coming from Titan's atmosphere.)

The H2O and CH4 are broken down by solar UV a lot more slowly, although
Spilker said that Cassini did indeed detect a large amount of OH in the
cloud from water breakdown. (The carbon released from the decomposing methane -- or, alternatively, carbon monixide also released from Enceladus' subsurface -- may react with the atomic oxygen to produce the carbon dioxide gas detected by Cassini, which is rather hard to explain otherwise given the low temperatures.) However, a lot of the water vapor spreads all the way around Enceladus -- and, in fact, out into the E Ring -- without breaking down, and then refreezes as those tiny particles of ice in the Ring, which are relatively even in size (unlike the power-law distribution of various-sized fragments of material in all the other rings, including the F and G Rings). Spilker actually dropped another tidbit backing this up: the CDA team has seen what may be an asymmetry in the distribution of water-ice particles around Enceladus, but are still trying to decide whether it's statistically significant.

A lot of that refreezing water vapor also forms the pure-water, fine-particle "snow" that seems to coat all of Enceladus evenly, including the parts that haven't ever had surface geological activity. (And is it possible that those big "boulders" that so surprised everyone in the very high-resolution photo of the active region are actually "snowballs", made of water-ice particles that are clumping together in the immediate vicinity of the vents -- maybe because of influence by the local high concentration of ammonia vapor?)

A neat picture -- although, of course, it does nothing to answer the billion-dollar questions: what's driving the heating that causes the vents, and just how much liquid water/ammonia mixture is there in the subsurface underneath them? There is, by the way, one hell of a lot of other interesting new stuff from Cassini/Huygens in the new DPS abstracts, brief as they are. More on those other items later.

[Guest_Richard Trigaux_*]

(The vents are probably those little dark speckles, near the cracks, that look like Enceladan blackheads -- at any rate, http://www.aas.org/publications/baas/v37n3/dps2005/450.htm says so.

Possible evidence for past cryovolcanism includes kilometer-scale ridges and linear arrays of rounded domes that appear to have extruded through preexisting surface fractures. Some wrinkled, flow-like features with lobate margins are found near the ridge and dome features, but it is unclear if they are volcanic flows or tectonically folded grooved-terrain. ...  Among the most mysterious newly-discovered features are small, sub-kilometer-sized dark spots and circular pits that sometimes cluster in a honeycomb like patterns near faults and scarps. Their origin is unknown, but perhaps the pits and dark spots identify sites of explosive venting of subsurface volatiles through fractures or volcanic conduits.

Has someone pictures of these features? These pictures must exist somewhere, otherwise there would be no comments about them. Thanks.

[Guest_BruceMoomaw_*]

It occurs to me that what I said about Emily Lackdawalla was very tactlessly phrased -- but, unfortunately, it remains true. Linda Spilker DID say that Ms. Lackdawalla completely misinterpreted what Spilker had told her, and she did say that she hadn't said anything remotely suggesting that the E Ring particles definitely did not come from the vents. She did say that the science teams themselves are still not entirely certain on that point -- but she added (as other members of this group have also said) that in that case it's very hard to see why Saturn's other moons aren't also producing comparable numbers of E Ring particles.

As for the Enceladan "blackheads", they turn up on a very large number of photos in all three close flybys -- they jumped out at viewers immediately even during the first, "untargeted" close flyby in February. Here's a few examples:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=45675

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=45662

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=34984

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=34976

[David]

It occurs to me that what I said about Emily Lackdawalla was very tactlessly phrased

Emily Lakdawalla (not Lackdawalla or Lacdawalla) recently joined this list. It would be a shame if she were to decide to leave it due to a failure of tact. While I appreciate the clarification of Spilker's comments, I think that criticisms or disputes between named individuals, unrelated to the facts themselves, might better be handled privately.

[Guest_BruceMoomaw_*]

Ms. Lakdawalla has indeed -- understandably -- hit the ceiling about my accusation. Another conversation I've just had with Dr. Spilker confirms that the key erroneous statement "So the vents are not the source of the E Ring" was indeed made to Ms. Lakdawalla, in just those words, by Dr. Spilker herself, because it was the tentative very early conclusion of the Cassini science team themselves (which they have now completely changed their minds about, on what would seem to be the obvious grounds that Saturn's other moons aren't throwing off E Rings of their own).

So Ms. Lakdawalla concocted exactly nothing; the error was entirely one by her source. My profound apologies to her. (Also, my embarrassed apologies for managing to misspell her name twice in a row. You'd think that someone whose name is misspelled as often as mine is would be a bit more sensitive to that point as well.)

[john_s]

Can I just say how impressed I've been with Emily Lakdawalla's coverage of Cassini on the Planetary Society Web site?

[TheChemist]

Quite an impressive U-turn from Dr. Spilker. I thought only politicians could pull these up

[Guest_BruceMoomaw_*]

The real story turns out to be, apparently, that Spilker stated so forcefully to Ms. Lakdawalla that the Cassini science team was certain that "The vents are not the source of the E Ring" that Ms. Lakdawalla jumped to the conclusion that the team had actual chemical-composition evidence to that effect. After which I jumped to the conclusion that she must have actually drastically misquoted Spilker in that line. In short, we both jumped to false conclusions as a result of the Cassini science team jumping to its OWN (seriously dumb) false conclusion immediately after the flyby, and then reversing it later.

[craigmcg]

I agree that the articles on the planetary society site are excellent. I hope to see many more like them!

It's good to see that whatever misunderstandings took place along the way, the facts (for lack of a better word to describe our present knowledge) are coming to the forefront.

[Guest_BruceMoomaw_*]

I will definitely go along with that. (I'll also go along with the statement that Ms. Lakdawalla's Planetary Society articles -- despite that one mistake -- have been excellent, and extremely useful to me personally.)

Now, then. Since it does seem highly probable that the E Ring particles are being expelled by Enceladus' vents, what are we to make of the sudden dramatic eruption observed by Cassini during its final approach to Saturn, which doubled the E Ring's total vapor mass for a few weeks before it dropped back to normal? We seem to have, just from this incident, proof that the vents are not just trickling out vapor at a very low constant rate, with the E Ring particles having a very long lifetime. Is the team looking for evidence in the Enceladus photos of a very recent venting event? It would seem the logical thing for them to do.

[elakdawalla]

Can I just say how impressed I've been with Emily Lakdawalla's coverage of Cassini on the Planetary Society Web site?

Aw, shucks. Thanks, everyone. It's a labor of love.

Thank you, Mr. Moomaw, for being willing to retract your statement publicly.

And don't be hard on Linda Spilker, everyone, she deserves a lot of credit. When she was talking to me it was still relatively soon after the flyby. Linda may be the Deputy Project Scientist but Cassini has an ENORMOUS science team involving twelve different instruments, and it takes a long time for the team -- even someone as involved as she is -- to synthesize what all of the myriad different data sets are telling you. I'm happy she was willing to talk with me and express her own excitement about what were then very premature and uncertain conclusions, rather than sitting and waiting and waiting to talk about anything until all the "i"s were dotted and "t"s crossed. Of course the story changes over time -- that's what the scientific process is about. It's exciting to be able to watch the story unfolding.

Linda told me today that part of the confusion is because the CDA team were confused about the implications of their own data right after the flyby (something about the timing of the observations or something, I'm not quite sure about the details). She also told me there's a CDA release coming out shortly that should clear some of this up, but that it's being held up because NASA HQ doesn't want to confuse the press with more than one story at a time, and the Shuttle trumped everything. That's a tale of woe I've heard before from many missions. I wish NASA would give us more credit, and respect that we can handle more than one story at a time!

Emily

[dvandorn]

I wholeheartedly agree with your sentiment, Emily. But we have to face the fact that we live in the world of the sound bite, the news cycle, and the MTV attention span.

Those of us who enjoy news of planetary exploration generally have longer-than-average attention spans and an ability to retain interest in a subject for longer than a single news cycle. But, more and more, I've come to the conclusion that we're the exceptions. Of course, we have resources like this forum with which to supplement what the organized media offer, and without it I think most of us would be going slowly insane...

As for my own two cents -- I'm glad to have both you and Bruce as contributors to this forum. I know that, even though you both write for special-interest publications, you have to keep your professional work at a certain level. Whereas here, y'all can get as detailed and as esoteric as you want, and anyone who wants any further background to help them understand just asks for clarification. It's refreshing and vastly more satisfying (to me and, I suspect, to a lot of the people here) than any other newsgroup, chat group, forum or single publication could hope to be.



-the other Doug

[pioneer]

I didn't know Emily Lakdawalla became a member

Glad to have you join us.

[malgar]

A view of Enceladus cracks.

[tedstryk]

Great work!