CICLOPS' Rev 49 Looking Ahead page is up. Highlights include a fourth monthy Voyager-class encounter with Tethys with 500m resolution over Odysseus (finally!)
Detailed mosaics of Rhea's prominent ray crater and points west are on tap for Old Scabby's second closeup. This should be a really cool periapsis passage to tide us over until the 10th of September.

Darn it, I'm kind of disappointed. I was expecting to see another one of your neat icy moon collages here.

Onward to Iapetus!

(... oh well, Rhea, too *yawn* ... )

I should that our Rev49 preview does not include the Iapetus encounter. Basically, it was decided to split up Rev49 since too many cool things were going on for them all to be done justice. So this preview covers the encounters around periapse up through Sept. 5 or so. We will publish an extra special Looking Ahead article just for the Iapetus flyby.

ugordan, LOL, so I guess if Rhea put on some dark makeup on her leading hemisphere and wore some equatorial jewelry, it would be "Onward to Rhea!" hmph, I guess Rhea will just never be as cool as her oblate twin sister, Iapetus.

Ooooh...double burn!!!

I've been taking belly dancing classes..."Equatorial Jewelry" has multiple possible connotations and would be an excellent name for a band as well.

Really looking foreward to seeing that whole crater and how old it actually is. Judging from the single WAC frame from 2005 of that area, Rhea is a lot more interesting on small scales than she looks from afar.

Gordan, a Hyperion multi-angle composite should be up tomorrow.

Gosh.... I second the darn it!!!!!!!

As soon as I see Exploitcorporations, I jump!!!!!!

I had an old friend who was a belly dancer... she would have appreciated Equatorial Jewelry... and Iapetus.

Truly look forward to Hyperion as done up by Exploitcorporations.

Craig

Latest Looking Ahead update is now available:

http://ciclops.org/view.php?id=3392

Features:

* Solar conjunction
* Stereo coverage of Tethys' Odysseus basin
* Targeted Rhea flyby focusing on its fresh impact crater
* T35 (3,302 km)
* Start of Iapetus encounter

As a matter of fact, yes.

We know they're both geologically as dead as the Monty Python parrot is, but at least Iapetus wears "makeup" and sports a strange figure. Rhea is just plain... dull. Oh, that and we already got a sh*tload of close Rhea images. Last time we flew close to Iapetus, we found unexpected stuff. What interesting bit have we found at Rhea yet?

Nothing to see here people, move along...

I think this dutch proverb is very appropriate:

"Even if a monkey wears a golden ring, it is and remains an ugly thing"

I don't often actually laugh out loud at things I see on the Internet, but EC's characterization of Rhea as "Old Scabby" at the top of this thread did the job.

As for Rhea vs. Iapetus -- There's no doubt that currently-active bodies will always be most interesting, but, failing that, ancient activity trumps no activity at all. (Unless the absence of activity is interesting in itself, of course -- but while that might be the case for Mimas, it ain't so for Rhea.)

Hey.. let's not give poor Rhea a hard time. She can't help looking like the ultimate battered wife.

Actually, Rhea IS interesting, but in horrendously subtle ways. Even the Voyager 1 close pass mosaics showed subtle lineaments of crater edges and features that simply aren't due to lighting effects <lighting CAN cause spureous lineations to appear> Something's "interesting" about the way Rhea responds to battering. Something makes the whispy features visible on the trailing side, only partially revealed to be due to subtle dione/tethys like fracturing.

It's a shame Rhea, the largest of Saturn's iceballs, isn't something semi-spectacular like Aerial at Uranus, but that's the breaks!

Some raws from the Rhea encounter are now up (hopefully some of the Tethys stuff a little later )
http://ciclops.org/view_event.php?id=66

http://ciclops.org/view.php?id=3705 shows the interior of the "young" ray crater. Not quite that young it would seem. [EDIT: not that isn't... but http://ciclops.org/view.php?id=3713 is]

Huh. This image seems to show a lobate flow with striations near the top center...interesting! (Can't believe that I just used the word "interesting" with respect to Rhea, but that's what exploration is all about... )

EDIT: Whoa! Look at this bright albedo feature with the dark spot! It actually looks young! Might have to drop the I-word & go with the F-word (fascinating!)

I'm confused, I don't see it.

Neither do I.

To the untrained (and low-phase-confused) eye, that would appear to be pretty young terrain. It looks almost as young as some of Enceladus' surface.

I think nprev's talking about the small double crater at top center, in the brightest portion of the image. It's got a darker floor which I'd personally attribute to shading instead of albedo difference.

Sorry for the confusion, you guys; let me try posting a clarification. If this works, I'm talking about the circled area, though the "dark spot" may be a semi-shadowed crater; the phase angle's pretty high:
Click to view attachment

Maybe if you drew an arrow to the features, that would help. All I see are craters. And more craters.

What is interesting, at least to me, is the lighter-toned substrate exposed by impact gardening and/or downslope movement on crater walls. We've see this on other satellites.

Okay. Yeah, the light-toned substrate is the "albedo feature" I referred to, and here's that silly dark spot (which I'm now convinced is merely a shallow crater):

Click to view attachment


Sorry for the tempest in a teapot...(we need an embarrassment emoticon, here...)

Some of the Rhea images are starting to show up on the JPL raw images page, including a beautiful WA set with Saturn in the background.

Nice! My quick'n'dirty versions of the first three sets...

Click to view attachmentClick to view attachmentClick to view attachment

--Emily

Not just craters on Rhea:

http://saturn.jpl.nasa.gov/multimedia/imag...3/N00090796.jpg

Crater chain or tectonic feature ?


Marc.

I've been saying for many, many months that Rhea exhibits more crater chains than I've ever seen on any other body in the Solar System. It has led me to speculate, here in this very forum, as to whether these chains are controlled exogenically (i.e., actual impact crater chains) or endogenically (i.e., tectonic features/fractures).

Note that the feature you linked to has a very small accompanying feature to the right and below (as this image is oriented). That much smaller feature is parallel to the larger feature. To me, that argues for endogenic control of these features.

I think that the rather large population of such chain features makes Rhea a lot more interesting than most everyone else here thinks.

-the other Doug

Highest resolution observations of Odysseus impact basin on Tethys:

http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=124822
http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=124817

That first one almost looks like it's got a rille or two in it, though I'm guessing it's just some fortuitous shadows.

Jason, I've seen this explained before but I keep forgetting the explanation. Can you explain the origin of the every-other-line truncation that appears in Cassini images that have lots of detail?

I love the sharp peaky shadows cast by the peak ring of Odysseus.

--Emily

A long and narrow crater chain (?) on Rhea:

http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=124693

Rhea sure has a lot of these features.

Are any of the commercial photo packages (like Adobe) able to interpolate and fill in the truncated lines? eg by averaging the surrounding pixels?

Here are the two Odysseus money-shots with the interlacing removed:

Click to view attachment

Click to view attachment

Ian.

Awesome composites, Emily!

Getting back on the horse after it threw me, as it were...(and if I'm being a complete clown, please somebody tell me so!!!)

Nice indeed, Emily!

Anyone else struck by the fact that the NW rim of Oydessus is practically worn into the landscape to the degree that it's virtually indistinguishable from the surrounding terrain? Means it's very old of course, but why just here? Was the impact a sort of glancing blow (i.e., oblique?), or did some sort of internal activity erase this portion of the rim, as well as a small segment in the SE quadrant?

The crentral peak area of Oydessus is slightly reminiscent of King Carter on the moon.

The truncation comes from the "LOSSLESS" compression scheme (obviously a bit of a misnomer since it can and does lose spatial information). The algorithm operates on line pairs and guarantees a compression ratio of at least 2. It's a variant of a Huffman encoder and if it figures out that the two lines it's currently encoding will turn out to be compressed more poorly than 2.0 ratio, it just stops and truncates the rest of the second line. In an absolute worst case scenario the second line could be completely truncated if the first line turned out to expand rather than shrink, which could happen since the algorithm uses fixed statistical encoding tables, they are not optimized for each frame.

I believe Voyagers also used something similar. Not sure if Galileo originally had it as well. It's a rather dumb and unflexible encoding scheme, but is computationally inexpensive so it's often used. The fixed 2.0 limit is probably due to ease of data policing on the onboard encoder - with LOSSLESS encoding you can guarantee that the frame will be at most half the original size so you can allocate space for each frame accordingly and not worry about losing the whole lower part of a frame in case your encoded frame turned out bigger than you predicted.

Here's another one for the photoalbum:
Click to view attachment

A rough 8 frame Rhea mosaic:

http://paranoid.dechengst.nl/saturn/Rhea-0...30-AUG-2007.jpg (1.8 MB)

It doesn't look too great with all the noise and stuff but a least it gives an impression.

The floor of the "young" ray crater on Rhea is really interesting.

http://ciclops.org/view.php?id=3713

Eastern part shows many small craters, but it seems that giant landslides completely covered the western floor where no craters are visible anymore. The ray crater seems indeed young and the landslides even younger.

The landslides or "snow flows" remind me a little bit what is happening on Jupiter's moon Callisto.
Both Rhea and Callisto are considered as the boring moons in their respective satellite system. I think it is really not the case.
Marc.

This WAC picture shows that the previously mentioned lobate flow was caused by an impact near the rim of the bigger crater (like on Callisto as I already mentioned).

http://saturn.jpl.nasa.gov/multimedia/imag...3/W00034593.jpg

Additional crater chains and other linear features are also visible.

Marc.

Yeah...I think you're right, Marc. Rhea may look bland globally, but these close-ups are revealing an amazing amount of complexity at smaller scales. The sheer number of linear features is really remarkable, as UGordan observed. Beginning to wonder how many of the features that look like crater chains might actually be collapsed "cryolava tubes" dating back to Rhea's boisterious youth...

Great mosaic stitchwork, DEChengst! Did you use any special software for this?
As for the noise, this showcases why histogram stretching for JPEG raws is basically a must for low contrast targets.

Not really. Just used Photoshop to interpolate the missing lines (deinterlace filter), levels correction and cropping off the white borders. Stitching was done with PTGUI and Smartblend. The stitching is pretty much automatic with just some manual tinkering with the parameters.



Yep. The raw images look pretty bland. This is pretty evident in the filesize. They're only 40-60 KB a piece, while normally you expect something like 100-250 KB. I guess I'll have to wait for the PDS release as I lack the Photoshop skills to fix this.

Would anyone here who's more familiar than I with the cratering rate at Saturn care to take a stab at estimating Big Ray's age?

See, now, I'm beginning to wonder if I'm a ghost and no one sees my posts except for me, LOL... I have been trying to get a discussion going about the linear features and "crater chains" on Rhea for something like a year and a half, if not longer, and not a single person has ever responded to my comments. Now it's ugordan who's noticed these things?

I remember taking images of Rhea and using my primitive image-processing skills and tools to outline the large chains, and then pointing out how these same structures seem to persist all the way down to the smallest visible scales. If I remember right, this was some time in early 2006. I've revisited the topic pretty much every time we get more decent Rhea images. Am I actually going mad and remembering things I never did?

That said... ...I am very, very interested in whether these features are endogenic or exogenic. If endogenic, Rhea becomes an extremely interesting little moon. Even if exogenic, you have to explain how so many crater chains, of all sizes and varieties, show up on this moon while they show up only much more rarely on the other moons of Saturn.

-the other Doug

Ummm... I think both of you have the wrong guy here. I noticed what? The linear features? I'm most certainly not the first one to point them out. I'm not sure when exactly I mentioned them without someone else pointing them out earlier... And I'm most certainly not claiming credit to discovering them.

That being said, yes, I took some notice of them in higher res shots. There are too many of them and appear to be too narrow to be a simple impact chain, IMHO. I'd go with an endogenic origin of some sort. At least for some of them. Then again, I'm not a geologist.

The collective amount of insight & expertise on this forum is so massive that it's damn hard to keep track of who said & did what sometimes...apologies, oDoug & UG!

Regardless, Rhea's linear features are indeed fascinating. I can't recall the precise image now, but one of the recent set showed a manifest crater chain that had a relatively large, very pronounced teardrop-shaped terminal "crater"...hard to see that this could be anything less than the result of a hybrid of exo/endogenic original processes, with probability tilted towards the latter.

It works pretty well to copy the area, paste it as a new layer, then nudge it one pixel up or down and select a filter that shows the max of the two layers' brightnesses. Basically, close the even numbered lines onto the odd ones.

Maybe I just haven't been paying close enough attention, but it seems to me the crater chain/linear features all tend to be awfully narrow. I haven't noticed any really obvious crater chains like the ones that are all over Callisto. Assuming I have been paying close enough attention, this would incline me toward an endogenic origin. (And for what it's worth, dvandorn - I remember!)

I've been casually looking through past Tethys images and there are similar linear features at a similar scale present there. They are, as you say, too narrow to be impact chains, but they do have that string-of-pearls appearance to them. Confusing...

Yes, there are some "chain" features on Tethys as well, but it's not as striking as on Rhea, and it always seemed to me that the ones on Tethys were near and generally radial to the big basin.

I also noticed some chain-like features in the only close-up images we have of Iapetus, but again, they're not as ubiquitous as the ones on Rhea. I haven't noticed the same thing at all on Dione or the older portions of Enceladus.

-the other Doug

A quick 11 frame crescent Rhea:

http://paranoid.dechengst.nl/saturn/Rhea-1...29-AUG-2007.jpg (1.5 MB)

Wow! Nice work.

I can't imagine what that terrain must look like from the surface - a global badlands of immense vertical scale.

Wow indeed! I always loved the crescent images and that mosaic is just incredible.

Badlands is apt. Place looks like a setting for some sky-fi about space smugglers or such.