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29-30 August 2007 Icy Satellites (rev 49), Last stop on the road to Iapetus
Phil Stooke
post Sep 5 2007, 12:57 AM
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My trick - select the area containing truncated lines. Do a select color range to get the almost or all black pixels. Move the selection area (not the pixels, just the selection) up one line so it's over the good lines. Copy and paste, and move down over the bad lines. Then repeat, moving the selection down a line, copying and pasting and moving it up a line.

Now I have three layers. Original with black lines, and over the black lines, one copy of the line above, one copy of the line below. The top one I make 50% transparent so the "line fill" is an average of the line above and the line below. Flatten and serve with a glass of red wine.

Phil


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volcanopele
post Sep 5 2007, 02:23 AM
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Another way is to use a boxfilter to null the pixels affected by the truncation. Then use low pass filter with a box size of samp=1, line=3 to have each nulled pixel be an average of the good pixels above and below it...


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ugordan
post Sep 5 2007, 07:36 AM
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Wow, great Rhea mosaic there, Emily!


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DrShank
post Sep 15 2007, 03:13 PM
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Crater Chains:
Ive noticed there are a lot of these long linear features as well on Tethys, Rhea, and Iapetus, and yes even Dione. Ive started doing some fits to them and most do line up as radials to big basins, tho not always the biggest one such as Odysseus. Smaller basins and craters produce such secondary impact chains. We see something similar associated 100-km size craters on Callisto. It is when they fail to line up that they get interesting. that is why the big chains on Callisto must be tidally split comets, since there are no basins they can be linked to. ill have more to say on all this later but am currently working on the paper so have to focus on that. i note that the theory of disruption predicts that there will be no split comets at Saturn, due to its very low density.....
cheers,
paul


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ugordan
post Sep 15 2007, 03:18 PM
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QUOTE (DrShank @ Sep 15 2007, 04:13 PM) *
i note that the theory of disruption predicts that there will be no split comets at Saturn, due to its very low density.....

I'd like to know more about this. Does Jupiter break up comets in the vicinity of its "surface" or much farther out? If the former's the case I can understand how Saturn's density plays in, but if the latter - does a less dense object behave differently than a dense one (given same mass) at great distance, i.e. do they both not act as point gravity sources?


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ngunn
post Sep 15 2007, 04:46 PM
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QUOTE (DrShank @ Sep 15 2007, 04:13 PM) *
Crater Chains:
i note that the theory of disruption predicts that there will be no split comets at Saturn, due to its very low density.....


How about a plunge through the rings, especially at a low angle? Could that not disrupt a comet?

Ugordan you're right about planets acting more or less as point masses, so I guess the theory Dr Shank mentions envisages Jupiter's disruptions happening pretty close in. The most uncertain parameter in any such theory must be the cohesive strengths of the comets. I wouldn't be surprised if there is a huge spread, and you might only need a few atypical ones at long intervals to produce the observed alignments on the moons. Therefore I'm a bit wary of the prediction quoted, even without the rings issue.

Interesting. I look forward to reading that paper - maybe here???
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DrShank
post Sep 15 2007, 06:44 PM
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i have to admit im short in the theory department. im only interested if they land someplace!
this all goes back to shoemaker-levy 9 days, now almost 15 years ago. breakup requires passage within about 1.5 jupiter radii of the surface of the planet, and something similar for saturn, except the density plays in somehow. the articles by asphaug, benz and others back in the mid-1990s tell all, otherwise start with the Schenk paper in Icarus in 1996 which includes such references. i dont have a copy with me at the moment, alas!
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paul


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alan
post Sep 15 2007, 07:43 PM
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If anyone is still interesting in looking at Rhea the closeup images that were mangled have been replaced by much improved versions.

Attached Image
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MarcF
post Sep 15 2007, 08:07 PM
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Did someone try to make the Saturn-shine mosaic of Rhea ?
Marc.
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ngunn
post Sep 15 2007, 08:52 PM
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QUOTE (DrShank @ Sep 15 2007, 07:44 PM) *
i have to admit im short in the theory department. im only interested if they land someplace!


Well, I'm sure this is obvious to you but for others who may be interested I'll just expand on the point I made in my last post.

Any comet which is going to collide with one of Saturn's inner moons after being disrupted at Saturn has to have been orbiting pretty close to the ring plane in the first place. That particular subset of comets is precisely the one with the biggest chance of a lengthy and damaging encounter with the rings. Saturn's low density means that its surface is further out than the radius at which the gradient of it's gravitational field is deemed sufficient to disrupt a comet (based on certain assumptions about the material strength of comets). I suggest that an encounter with the rings presents a viable alternative mechanism whereby a comet in the right kind of orbit could be disrupted and then form a crater chain, streak or whatever on an icy moon.

In fact it could well be that for the special case of comets orbiting in their respective planet's equatorial plane Saturn (plus rings) is better at disrupting them than Jupiter.
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stevesliva
post Sep 15 2007, 09:25 PM
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QUOTE (alan @ Sep 15 2007, 03:43 PM) *
If anyone is still interesting in looking at Rhea the closeup images that were mangled have been replaced by much improved versions.


Unless you consider those phase angles that make the concave look convex to be "mangled." unsure.gif This may motivate me to actually download some photos to invert them.
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scalbers
post Sep 16 2007, 10:18 PM
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Alan - glad to see the raw image improvements. I had sent in an email to the link on raw images page on Sept 2 about the raw images stretching issue. I received a nice reply on Sept 10 saying they were about to fix the stretching and would retroactively reprocess the S33 images. This was caused in June as an inadvertant side effect of stretching improvements they were implementing.

They thanked me for "catching" this. I wonder how many others had reported it to them (either internally or externally).


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dvandorn
post Sep 17 2007, 04:24 PM
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You also have to wonder whether or not the whole fiasco was indeed a simple error. After all, we know that many people on the Cassini imaging team have been less than happy about feeling "forced" to release real-time images.

I'm not a big fan of paranoid speculation, truly... but I can just see a few specific people snickering to themselves and gloating, "Just let those &^%#@! UMSFer's try and scoop us to our pretty processed images with THIS stuff!"

rolleyes.gif

-the other Doug


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djellison
post Sep 17 2007, 04:36 PM
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I don't believe the conspiratorial stuff for a second I'm afraid. I know the head of Cassini outreach personally, and she wouldn't take that sort of nonsense - believe me.

The UMSF admin team (Well, Bjorn and Emily) asked about it and it got fixed shortly thereafter.

Doug
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dvandorn
post Sep 17 2007, 05:09 PM
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Oh, trust me, I don't seriously believe there was anything like that going on. Just that some peoples' public statements on the general subject could lead the conspiracy-minded to that kind of conclusion.

The lesson, I guess, is that when you go on record as having a given minority view, and you could possibly have some influence on future events surrounding related issues, you have to be more careful than normal to avoid even the appearance of wrongdoing... unsure.gif

But, as I said, I'm not seriously suggesting anyone actually messed up the raws in order to make then unusable by amateurs. Just that the appearance of wrongdoing is invited, and could be pursued by the conspiracy-minded, because some people have aired such views. Actually, on the larger conspiracy front, I'm a little surprised that the Hoaxland crowd never jumped on the image quality issues by screaming "What are they trying to hide?????!!!!!"

-the other Doug


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