Just as a skeptical hypothesis, I wonder if this cometlike halo could be due to the summation of light coming from Dione plus some generalized light leak placed to the right.

Some nice Dione images from Rev 27:

crescent stitch
http://www.members.optusnet.com.au/ics_gs/...4755_mosaic.JPG

night side

http://www.members.optusnet.com.au/ics_gs/...0064758_mod.JPG

That's probably about right. All Cassini images exhibit an ever-so-slight halo around bright objects. I don't know if it's an inherent "feature" of the narrow angle camera or residual haze traces or simply diffraction/PSF effects. Probably a bit of everything. In any case, if the Dionian hypothetical plumes are real and much weaker than Enceladean (as it's been suggested), about the only way to see them would be to occult the Sun so there's no illuminated crescent visible. No saturnshine would be a bonus, too. Even then, it's a question of the plumes themselves being in sunlight. That's a lot of geometry constraints.
AFAIK, this is not going to happen since Cassini already executed its dedicated Dione flyby and is left with only a couple of distant flybys in the primary mission. The chance of the geometry being such that Dione will occult the sun is miniscule. We're likely stuck with only hints of activity from the magnetometer readings.

I agree about the weak, estended halo similar to a cometary coma: probaly it is an artifact due to sensor + spurious light diffusion.
I was talking about the inner, "blue" (referred to 2nd image) halo within 1 Dione radius, which appear elongated and not exactly allineated to the Sun illumination... but, yes, I still in doubt about real interpretation and, yes, probably the only way to know is through unprogrammed eclipse...
What about magnetometer readings?

Also very last images of Dione limb are odd, with a glare not aligned with Sun direction...
http://saturn.jpl.nasa.gov/multimedia/imag...3/N00064895.jpg
I do not have photo-elaboration instruments in order to betteer see weak details but the fact they are still taking lot of images like this is a clear hint that they search/suspect something on Dione volcanism, IMO

Perhaps I have to step back on my last post... more careful analysis of entire sequence showed that, probably, glare is simply due to higher albedo in the left portion, as clear from this lower exposure:
http://saturn.jpl.nasa.gov/multimedia/imag...3/N00064886.jpg
anyway, they are still taking lot of images like this.

Well, it's not like they can choose NOT to take very high phase images right now

Some new hints about a current Dione internal activity from the 38th annual division for planetary science meeting :

Oral session 72
abstract presentation 72.01, Gerald Schubert.
Interiors of Enceladus, Dione and Rhea
http://www.abstractsonline.com/viewer/view...2-AB52D1F706C5}
Marc.

Thought I'd mention a Dione map update using one of the July, 2006 images (as suggested in another thread). The URL for my latest map is:

http://laps.noaa.gov/albers/sos/sos.html#DIONE

A little reminder of the Voyager 1 Dione flyby, a long time ago:

http://saturn.jpl.nasa.gov/multimedia/imag...fm?imageID=2333

Marc.

Golden oldies, in anticipation for the 21 November encounter...if there was one. Here's the 15 December 2004 high-res view, with a few enhancements thanks to Mr. Albers and Celestia:

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The Padua Linea mosaic in wide-angle context (11 October 2005):

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I reiterate my support for the term 'Enceledosian'.

It sounds more alienesque.

I think I prefer "Enceladan"...

-the other Doug

I just came across these today, and don't remember having seen them at all before. They obviously seem to have been taken at the same time as the crescent mosaic. Just wanted to share:

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I did a quick 'n dirty ir3/grn/uv3 combo to create a "color" image of the latest Dione flyby on april 24th, then I stitched them together.

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Below is a simulated view of the same scene, using Steve Albers' map and xplanet.

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Here is a recent Dione mosaic compared to the Voyager high resolution mosaic. It is amazing how illumination effects crater visibility. The first link is to the full resolution version, the second link is to one without the lines showing the craters I am talking about.



http://www.strykfoto.org/outericymoons/dioniillumarked.jpg

http://www.strykfoto.org/outericymoons/dioniillu.jpg

Ted,

Yes I agree that illumination has an important effect on crater visibility. This area in particular was a consideration in prioritizing images for an updated Dione map version that I just posted on my website. I may want to tweak this some more, we'll see. The update is at this URL:

http://laps.noaa.gov/albers/sos/sos.html#DIONE

It really is a troublesome area. By the way, here is the full resolution version of my Voyager mosaic, in case it is useful.

http://www.strykfoto.org/outericymoons/vdionef.png

This mosaic has been officially released:

http://ciclops.org/view.php?id=3214

I have to say this is one my favorite views of Dione. A version of this image has been my desktop background for a while now.

While geometrically correct, I dislike the jaggedness at the limb these reprojections produce. It makes the mosaics look too artificial. I'd personally much prefer if the limb at these positions was slightly blurred/antialiased in Photoshop, the images are for public consumption and not scientific analysis anyway.

That said, this part of the release puzzles me:
A monochrome image created with IR/GRN/UV filters?

Yeah, that is an unfortunate side-effect. But I would rather that than not have the images align correctly. I stumbled on a solution when working on the until recently missing Tethys images, make my software think the radius of the satellite is bigger than it actually is. This caused my software to reproject the black background and Tethys, making the actual limb look at little more natural. Not my intended result, and if I were really working on Tethys maps, I might have complained a bit more.

Yeah, the image was a UV3/GRN/IR3 (or was it IR1..., grr, I can't remember) image, but rather than make it color ratio image (as has been done to similar false color images), it was made into a greyscale image.

Um, why not just release the stretched color composite as is since you've gone through the trouble of producing it anyway? It would nicely show the grayness (or is it "brownness" in IR/G/UV, I forget) of this moon.

Yes this is a good one to add in - thanks much. You can see how it looks now on my updated map at this URL:

http://laps.noaa.gov/albers/sos/sos.html#DIONE

That is an outstanding version of the V1 Dione mosaic, Ted. The new map looks wonderful...that nasty seam between the Cassini and Voyager coverage has all but evaporated with the April imagery. It looks like there may be an opportunity to plug the remaining lower-resolution gap in September.

Click to view attachment

Thanks EC for the September preview - I'll keep an eye out for that. I also found your Dione poster to be inspirational and helpful in figuring out the image coverage from recent flybys. There are perhaps further clues lurking therein.

Thanks! I had an earlier version of the Voyager mosaic I made, but I foolishly made it in 8-bit mode, and lost a lot of the benefit of stacking the images three-thick (I didn a super-resolution style processing, although I think the boosted SNR and more precise grayscale are the real improvements.

Dione images from December 19th are up: nice global view of the Odysseus-like basin:
http://saturn.jpl.nasa.gov/multimedia/imag...6/N00098820.jpg
Marc.

Here's my IR-Green-UV composite:

Click to view attachment

Edit: changed the orientation so that the south pole is now at the bottom of the image.

I wonder where this alter-Odysseus has been hiding all this time. Perhaps it's the roughly depicted basin near 70S 210E on this map?

http://laps.noaa.gov/albers/sos/sos.html#DIONE

It wasn't hiding at all, it was seen back in 2005 when Cassini was still spending most of its time below the ringplane.

Interesting Gordan, this is a good refresher for me on this basin. I'll have to consider adding the recent imagery to my map to see how much detail can be added. I've been using some raw imagery from the June 2005 flyby that you show above. Part of the basin rim appears to be overlain (and hidden) in the map by some low phase angle imagery (albeit at high resolution). Perhaps I can try to rework the image priorities to show a little more of the rim, particularly the northern portion. It looks like this was done in the official version. The Dec 2007 imagery looks like it will again benefit this northern rim area.

Taking a south-polar projection look at the map may be of interest in this assessment. Some features have the appearance of emanating from this basin.

(Edited 9:27PM UTC)

A tip on using Cassini images of gray targets like Dione for mapping purposes: the wisest choice would probably be the green filtered images ("CL1/GRN" for NAC and "GRN/CL2" for WAC), not clear filter, due to chromatic aberration issues. This especially goes for wide angle imagery. The point spread function is by far the tightest through that filter combo for WAC and to a lesser degree it's also the case for the narrow angle camera. The aberration is IIRC caused by field flattening optics (in the NAC at least, WAC is one big refractor anyway) and it was optimized for the visual wavelength range, centered at the green bandpass.

Thanks for the tip. I think I can see a slight improvement with the GRN filter on the Dec 2007 imagery, particularly near the limb.

This explains the apparent fuzziness of the basin in your maps, Steve...I always wondered why it wasn't more clearly defined. This feature is pretty subdued, but noticeable in Cassini pics as far back as May 2005. If I remember correctly, Phil identified this basin from Voyager imagery years ago. There are excellent high-resolution views at low phase angles obtained during the October 2005 encounter as well. It just seems to disappear from certain perspectives because the relief is so low. Dr. Stooke also stated here that features radial to basins like this are likely ejecta patterns rather than fractures (the "cat scratch" troughs near "Joan" on Iapetus are almost certainly of the same stripe IMHO). The Saturnian system seems like a remarkably good place to inventory large impact structures and related landforms across a broad range of ages and scales ("Claude" looks fresh enough to lick the frosting off of, and "S. Tirawa" looks old enough to make a Trilobite feel youthful).

LOL, I like that. The Saturnian system seems to be a encyclopedia of Things That Go WHUMP. It seems to have taken the LHB and improvised a few bars...

--Bill

Yeah, I get that impression, too. Maybe the rings are all that's left of a WAY bigger cloud o' rocks that beat the moons until their morale improved a few billion years back. (Must've worked; you don't hear them complaining now... )

Here is a Celestia view of my current map, centered on the basin of interest. It looks extra large from the close perspective:

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I think the Oct 2005 high resolution imagery is being used just in the northern (upper right) section at present. It is a bit tricky (as mentioned in post #82) since this is a low contrast region of that mosaic. Hopefully I can still make some improvements though.

Some of those features streaming off to the lower left may be only quasi-radial?

Steve (younger than a trilobite)

I like this view. With the December 19th pictures, I'm sure you will be able to make some improvements, Steeve.
The whole rim and internal structures are for the first time clearly visible, with a lot of details.
Marc.

New images are up. http://saturn1.jpl.nasa.gov/multimedia/ima...0&storedQ=0

I hope more images will follow, since this flyby greatly improves our map of the north pole of Dione.

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Unfortunately I think that may be all there is on this flyby - the pointing seems to be a little off, as some frames duplicate coverage of craters Dido, Romulus and Remus (towards the 'western' limb), using the same suite of filters in each case.
Hope I'm wrong though..

Jase

Just in case, perhaps there's another opportunity to show this region on Feb 8th?

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Greetings,

I've made a few updates to the Dione map, the latest being from 1/11/2008. There were a few additional images from the recent encounter after all, and one of them from January 3rd helps fill in the dione incognita near the north pole.

This version also has a reworking of the image priorities (plus the addition of a Dec 19th image) in the region of the southern basin we've been discussing. Hopefully some of it is more easily visible now. There is still a bit of a tradeoff between resolution, phase angle, and solar elevation for the northern rim. Here is a southern Celestia view...

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The updated version of the 4K global cylindrical map is at the URL shown below:

Click to view attachment

http://laps.noaa.gov/albers/sos/sos.html#DIONE

That's the latest (edited 1/12),

Steve

There's a somewhat interesting spot visible in this recent raw imagery. It's bright in UV and is incospicuous in GRN and IR imagery. It's not an artifact of raw images, it's visible in polarized UV as well and it moves in the FOV following Dione so it's not a cosmic ray hit or flatfield effect. This UV-only-bright property sets it apart from many other UV bright features like fresh crater walls and other brighter splotches. I've located the spot in older imagery from the PDS as well, confirming it's a real feature:



Does anyone have an idea what kind of process would produce such a feature in the ice? My first thoughts are that it must be a very fresh impact crater. It's detectable in Ian Regan's composite in post #79 as a bluish spot in otherwise yellow terrain in his composite.

Dione, Rev62:

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Rough merge of green filter sunlit image and clear filter saturnshine image.

I can't wait to see that made from real raw data!

I ran the flyby in Celestia and I see this is showing us more of the unknown northern terrain. Cassini has been approaching even closer this morning, so perhaps we'll see some higher resolution imagery coming up? On the other hand, the "Looking Ahead" section on the CICLOPS page mentions just the above observations at 665000km range on March 22.

Voyager 2 got a pretty good view of this area.

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Here is a possible Cassini view from 0600UTC today, that would add more to the map it seems. The sunlight would be on the opposite side of the north pole compared with the lower res Cassini view shown in post #96. I think the Voyager view above is reflected in my current map (3/13/2008 version).

So overall this flyby covers many longitudes around the north pole, if there is sufficient imagery being planned. As per the Celestia depiction, Dione could potentially be filling the NAC field of view around closest approach.

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