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Posted by: Decepticon Mar 27 2005, 06:08 PM

Here's a nice look at Rhea. http://saturn1.jpl.nasa.gov/multimedia/images/raw/casJPGFullS09/N00030797.jpg


Tethys @
http://saturn1.jpl.nasa.gov/multimedia/images/raw/casJPGFullS09/N00030798.jpg

Posted by: Sunspot Mar 27 2005, 10:57 PM

Another here:

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=35770

Posted by: Decepticon Mar 30 2005, 12:48 PM

Dione http://saturn1.jpl.nasa.gov/multimedia/images/raw/casJPGFullS09/N00030832.jpg

Posted by: Decepticon Mar 31 2005, 02:17 PM

http://saturn1.jpl.nasa.gov/multimedia/images/raw/raw-images-list.cfm?browseLatest=0&cacheQ=0&storedQ=0

Nice.

Looks like area seen buy Voyager.

Posted by: DEChengst Mar 31 2005, 06:03 PM

Nine frame Rhea mosaic taken at approximately 138,000 kilometers distance:

http://paranoid.dechengst.nl/saturn/Rhea2.jpg

Posted by: volcanopele Mar 31 2005, 06:18 PM

Would you mind if I posted a link to that on my blog? Very nice work. Even faster than me, though I have the excuse of someone not getting of the computer room mac

Posted by: DEChengst Mar 31 2005, 07:11 PM

Ofcourse I don't mind. The image is intended for everyone's enjoyment

Btw, do you know what way to rotate the image so north is up ?

Posted by: volcanopele Mar 31 2005, 08:05 PM

Counter-clockwise - 90 degrees

Posted by: DEChengst Mar 31 2005, 08:17 PM

Yes sir !

Posted by: dilo Mar 31 2005, 10:53 PM

Another Rea mosaic from 160000Km (starting from N00030889/90/91):
http://img205.exs.cx/my.php?loc=img205&image=reamosaic6ms.jpg
Regards

Posted by: scalbers Apr 1 2005, 12:04 AM

Greetings,

I've been updating my satellite maps, most recently with Rhea. I have the 3 images from today
taken at about 90 degrees phase angle. The next step will be to add some of the others nearer
to closest approach. You can check out the latest at this URL:

http://laps.fsl.noaa.gov/albers/sos/sos.html#RHEA

Nice to see the mosaics posted on this thread as well.


Later,

Steve Albers

Posted by: volcanopele Apr 1 2005, 12:15 AM

That's the ray crater near center

I guess I should ask the same question as DEChengst, do you mind if I post this on my blog?

Posted by: volcanopele Apr 1 2005, 01:09 AM

I have this better illustrated on my blog:

http://volcanopele.blogspot.com/2005/03/rheas-ray-crater.html

Posted by: dilo Apr 1 2005, 08:24 PM

Hi VolcanoPele, unfortunately I cannot visit often the Forum (I would like! ), so my replies cannot be in real time...
Sure, you can use my mosaic or other images I posted!
Anyway, wath about Titan T4 close-up images??? I don't see anything anywhere!
Regards...

Posted by: volcanopele Apr 1 2005, 09:10 PM

Images are on the ground and I'm starting to process them, but work is going slowly on them Not on the JPL raw images page yet

Posted by: dilo Apr 1 2005, 09:26 PM

Thanks, could you please tell the JPL raw images page URL? Regards.

Posted by: DEChengst Apr 1 2005, 09:40 PM

http://saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm

I noticed you did not fill in the lines that are missing because of the compression. You can fill them in using the de-interlace filter in Photoshop. I did the same mosaic as you did but filled in the missing lines:

http://paranoid.dechengst.nl/saturn/Rhea3.jpg

Posted by: dvandorn Apr 2 2005, 12:23 AM

I see a relatively large number of long crater chains -- including one just on the lighted side of the terrminator which looks like a huge gash in the side of Rhea.

I've seen a lot of crater chains on the other icy Saturnian moons, too.

Seems like we see more crater chains on these moons than we see on other solar system bodies of similar size. Including comparable Jovian moons.

My understanding is that such crater chains are thought to form when an impactor breaks up due to tidal forces (or due to an earlier encounter with a steep gravity gradient) but whose pieces fly along relatively closely-spaced until they impact another body. Rather like the way Shoemaker-Levy 9 broke into a "string of pearls" formation of comet chunks. Of course, there is always the alternate interpretation of such crater chains as endogenically controlled series of maars, though I'm not sure how that would work on an icy moon.

Any theories out there on why we're seeing more evidence of this kind of thing (i.e., the crater chains) in the Saturn system than we have seen anywhere else in the solar system?

-the other Doug

Posted by: Gsnorgathon Apr 2 2005, 02:15 AM

If they're crater chains, they've very degraded crater chains.

I don't see why they can't be endogenous - when an icy moon's interior cools, it's going to expand, and you'll see structures like Ithaca chasma on Tethys. It seems likely that there would be ancient degraded remains of grabens on icy bodies.

Posted by: dvandorn Apr 2 2005, 04:55 AM

These don't look anything like grabens to me. Yes, some are degraded (the larger craters tend to overly the crater chains), but many of them seem to be made of individual craters, lined up shoulder-to-shoulder for tens of kilometers, as sharp and fresh as any of the other craters on Rhea's surface.

Just so I know we're all looking at the same things, I drew red circles around what I'm calling crater chains. Note that most of them tend to be organized along the same general direction, with one obvious exception:



When I zoom in on this image, the linear features I'm calling crater chains really look to me like they're made up of tens of individual craters... and while degradation varies, especially in the uppermost feature, they seem no more degraded than the majority of the non-linear-aligned craters in their vicinity. (The "gash" I mentioned is the lowermost feature, halfway obscured by the terminator.)

But they don't resemble any graben I've ever seen.

So, what do y'all think -- endogenous or impact features? And if impact, how did so many align along the same general trend?

-the other Doug

Posted by: Gsnorgathon Apr 2 2005, 09:32 PM

Well, looking at the feature at upper left, I see what you're talking it about. It definitely looks crater-chain-like ("catena-like"?) especially at the far end. The fact that most of the features you've highlighted have a similar orientation still suggests structural control to me. :@P

Posted by: dvandorn Apr 2 2005, 09:53 PM

Yeah -- most (though not all) of the crater chains *do* seem to be organized along similar orientations relative to Rhea, it's true. And that does give them the appearance of being endogenically controlled.

I have an image, however, of some type of gravitational interaction flinging a stream of ring particles out of their orbits and out into the realm of the icy moons. Assuming there was no out-of-plane vector associated with the interaction, such a stream of particles would strike a moon along the ring plane, leaving chains of craters in its wake. The fact that these crater chains are no longer aligned with the ring plane could invalidate that theory, or could simply mean that Rhea's orientation to the ring plane has changed since a majority of the crater chains were formed.

On the side of structural control, we've seen these kind of "cracks" in the crusts of most of Saturn's icy moons, though in most cases they don't appear to be formed by chains of individual craters. And as they say, zero, one and many are significant findings, but "a few" means you probably don't have a complete dataset. In other words, if two other Saturnian icy moons display endogenic cracks modifying their surfaces, and we see what appear to be similar (though not identical) cracks on Rhea, the odds are high that the processes are interrelated, if not the same...

I think the jury's still out as to the formation of these crater chains, but the more data we collect, the closer we get to coming up with better theories...

-the other Doug

Posted by: Mongo Apr 3 2005, 04:22 PM

When I looked at that image, the first two things that jumped out at me were:

1) the visible crater chains are almost all parallel with the terminator

2) the crater chains are all fairly close to the terminator

I think that we are looking at the effects of lighting here. All the crater chains (with one possible exception) are oriented in such a way as to be most visible, given the location of the sun.

It seems quite likely to me that these crater chains are oriented in random directions, but only those locared close to the teminator, and roughly parallel to it, are visible.

Bill

Posted by: volcanopele Apr 3 2005, 07:50 PM

a paper by Jeff Moore et al. in Icarus (I can send it to any who wish to have a copy), suggested that fractures like Pu Chou Chasma (the upper right most of dvandorn's outlines) are radial to a 250-km wide crater near 25S, 155W, west of the ray crater in DEChengst'a second Rhea mosaic.

Posted by: dvandorn Apr 4 2005, 01:51 AM

I have a hard time believing the crater chains are simply lines of secondaries. The dynamics are all wrong.

I assume Moore et. al. are suggesting these crater chains / chasma are basically cracks caused by a large impact? Some of the chains are indistinct enough that I could believe it, but the younger ones (especially the one in upper left of the image being discussed) are obviously chains of circular depressions. And while diatremes could form a series of circular depressions along a fault line, how do you get diatremes without volcanic activity? I don't see any other evidence of cryovolcanism on Rhea (unlike what we see on Enceladus, for example).

Remember, a lot of people were absolutely convinced that the Davy crater chain on the Moon *must be* an endogenically-controlled chain of diatremes, but the data indicate that they'r really just a chain of impact craters. I think Occam's razor suggests these chains on Rhea are also chains of primary impact craters.

Both of my main concepts for how Rhea could develop such crater chains as direct primary impacts -- streams of outflung ring material and/or tidally shattered fragments -- can account for such chains seeming to lie radially away from a central larger impact. All you have to do is postulate a stream of roughly similar-sized fragments with one significantly larger fragment embedded within it.

Besides, it really looks to me like many of these crater chains are closer to parallel than being arrayed radially to a given point -- though until we get better global coverage, that's harder to pin down.

-the other Doug

Posted by: Decepticon Apr 19 2005, 01:42 PM

This was taken on march 7.


http://ciclops.lpl.arizona.edu/view.php?id=948