With Cassini reentering the ring plane for the upcoming series of icy satellite encounters (crowned with the Iapetus flyby in September), it seems like a good time to open a few threads on the state of imaging coverage of these worlds and post on the new results as they come in. I'll start by picking on Tethys as we haven't seen anything new since December.

This is part of a poster project summarizing global and near-global views of the icy moons. All natural color images here are the work of ugordan with the exception of the first (Mattias Malmer) and the last (CICLOPS).
This will be replaced with an annotated and expanded version as time allows:

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The optical navigation image from 11 May is the first clear view of Tethys since December. The subdued peak ring basin is nicely positioned on the terminator, with Penelope on the limb and Melanthius just out of view. The limb looks distorted in that direction, with the sort of troughs extending away from it seen in views of Dione's large basin. One of them crosscuts the deep crater visible in the high-resolution mosaics from the September 2005 flyby.

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nice collection there!

I know a great opportunity is coming up in the next orbit in late May. Some really nice images of everyone's favorite Giant Ball of Ice are possible then.

Very nice. I'll grant you that the maps that people have been making by projecting the different images and pasting them together are very nice. Amongst their other uses, those maps help visualize what areas have been well mapped, and which are still photographed in low (or nonexistant) resolution.

But I find seeing the original (and unprojected or distorted) pics to be more interesting than looking at a map, so this montage is really fun to study.

One thing that occurs to me (and this is NOT a complaint). A montage like this one, with some longitude and lattitude lines projected on each image, would be a great tool to help the viewer determine what angles he is looking at, and for studying the relative position of different features. I'm sure someone somewhere is working on such a project, and I look forward to seeing it someday.

Thanks again for sharing.

Cool montage, exploitcorporations, and I'm looking forward to more.

Are you using the PDS data or the raw data?

--Emily

Now that we finally have the May 26 images to play with, I can share why I was chewing my toenails off waiting for them. This composite shows the context for the nested high resolution images obtained during the quasi-targeted flyby in September 2005. I've excluded the first pair from the series because the WAC frame is saturated and the corresponding NAC view is underexposed (not to mention they don't fit anywhere I can figure out.)

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Fantastic work Exploit! Your Galileo/Cassini mosaics are truly outstanding!

But Tethys itself, well, I think it's trying to beat Rhea as 'Most Boring Moon' in the Solar System.

Really nice presentation, EC. What an excellent way to put those images in context. I think Edward Tufte would approve. Thanks!

Emily

No real disagreement there OWW... In terms of visual kick, Tethys rocks the party about as hard as a fistful of valium chased with a bottle of NyQuill™. Nonetheless, the linear troughs in the top middle frame and the differences in crater density across the three little windows here are intriuging. The right hand image looks down on part of the Ithaca Chasma system in exquisite detail, and there's nothing but ancientness to look at. I wonder what this mass of cliffs looked like when it formed.
Thanks for the compliments both...Emily, I was unfamilliar with Mr. Tufte's work, but we clearly share an affinity for the Century Gothic font.

Side note: I like how this illustrates the difference in FOV between the two cameras, and it makes me nostalgic for Galileo's tightly focused strips of images.

Wow, nice work EC, I hadn't really thought about those Tethys high-res shots.

Yeah, Tethys isn't exactly the most exciting place in the Solar System. About the only thing cool about it is that it literally is a giant ball of ice, the density is so low that it is hard to add any rock without adding some pore space, which seems unlikely given Tethys' size.

In a bubble, yes, Tethys is boring. But there seems to be a Rhea-Tethys-Dione-Enceladus progression emerging.

Yup. I've thought of Dione as Tethys on crack for a while, and Enceladus as..well, no need for mixed metaphors. Hopping over to community chitchat to start the Most Interesting/Most Boring thread.

Can I add to the chorus of approval EC - I wish I had your image processing skills!!
Tethys was my second favourite (Enceladus first) based on Voyager coverage. I can't tell you how disappointed I was with the V2 camera malfunction which prevented the hi-res Tethys mosaic. But having waited 25 years, I'm really enjoying seeing the blanks filled in for this little moon. I think it's anything but boring - very large craters, albedo differences, Ithaca Chasma etc etc.
Mimas is my candidate for the Saturn system's most boring moon - if it wasn't for Herschel........

Much of my interest in Tethys stemmed from that teeny corner of the disc being revealed.The cause of the lost mosaic was well explained by edstrick somewhere a ways back...the images were taken but all but one were of black sky because Tethys wasn't where the scan platform was pointed at the time, much like the early Cassini nontargeted flybys of Dione and Enceladus where portions of the disc were missed due to position uncertainties. The albedo and cratering differences kinda make Tethys look "inorganic" to me...it reminds me of one of those digital image maps where the lighting and resolution changes from region to region.


I would really like anyone to explain how the viewing geometry in the pair of images below is possible. Both have north at the top, both are taken from below the ring plane, both show Tethys in the sky just beyond the eastern limb of Saturn. How is it you see Odysseus in the top frame and the Ithaca Chasma hemisphere in the bottom one? This has bugged me for ages. I'm sure it has to do with Cassini's position in it's orbit, but I can't visualize it.

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EDIT: I just felt like slapping my forehead hard enough to knock my eyeballs out. It's because Tethys is on the other side of Saturn in the bottom one, huh?

Yep, Tethys is on the near side in one image (upper, see also this image) and on the far side in the other. Narrow FOVs can play tricks on the eye, can't they?

It's the same reason this photo has Jupitershine on Io and Europa is dark.

http://www.unmannedspaceflight.com/index.p...st&id=10490

Sorry, couldn't resist!

Guess there are quite a few 2007 Tethys images to catch up on in my mapping. Here's a map version from 1/31/2008 with an image from the September 2007 flyby added:

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Full res version at http://laps.noaa.gov/albers/sos/sos.html#TETHYS

It's interesting that Tethys is nearly as ellipsoidal as Enceladus. As I get more images to match together this will be worth taking into account. I understand that Tethys' circular orbit would preclude tidal heating.

Steve

Steve, I noticed you posted a new map of Tethys on your website, with a big improvement of the Odysseus crater.
What was the image you used to update your map?

The lower portion of that image doesn't seem to line up.

As for Odysseus, it looks much better now.

Greetings,

Yes I've been gradually taking stock of the Tethys imagery in light of some helpful advice that I've received. The latest image added is a mosaic IIRC PIA08400 from 8/29/2007. It should line up fairly well in the Odysseus area. It's possible there's a bit of misalignment of images adjoining it in the south. It could take a little doing to reorient some of the imagery; the largest navigation errors may actually be in the trailing hemisphere (judging from the latest official map).

I did post a new version again on 2/16 at this URL:

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

I'll continue to assess whether there are other images out there that could add details. Meanwhile it's interesting to see the darker band in the new image and how it's approximately centered on the equator in the leading hemisphere. Perhaps this has already been discussed, though it almost seems like a very much subdued version of Iapetus?

Steve

'Tis the season for mapping updates of Tethys - a nice version was posted at the CICLOPS website on Feb 20:

http://ciclops.org/view.php?id=4790