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Posted by: Exploitcorporations Aug 28 2008, 03:37 AM

In the excitement leading up to the Iapetus flyby twelve days later, the 5000 km-range nontargeted Rhea encounter (49RH) recieved relatively little attention here. As we all know, Rhea is the most dynamic and thrilling of the worlds in orbit around Saturn, and I'm certain that the short shrift it's been given infuriates you all to the point of aneurysm. A combination of sucktastic downsampling on the raws page, smeared Saturnshine, and equatorial-ridge envy doomed this beautiful visit to oblivion. As I've had the pleasure of taking a day off to play with these (thanks Emily for that awesome Selected ISS Data page!) I'm proud/drunk to present The Forgotten Flyby.

Posted by: Exploitcorporations Aug 28 2008, 03:46 AM

As Cassini approached between 66,000 and 48,000km from Rhea, 32 clear-filtered frames were accquired of the sunlit crescent and the nightside illuminated by Saturnshine. The 12-frame crescent mosaic is as far as I know the largest of the crescent views taken by ISS during the prime mission.

ISS_049RH_CRESCENT001_PRIME:

Posted by: Exploitcorporations Aug 28 2008, 03:59 AM

The 20-frame Saturnshine attempt seems to have been smeared into uselessness, but a few bright spots remain. Three of the images are fairly clean, providing the best view to date of a portion of the Izanagi basin and the nearby curious linear feature as well as a few of the icy cliffs in the north. This is complete composite of all 32 footprints.

Posted by: Exploitcorporations Aug 28 2008, 04:19 AM

Just past the point of closest approach, the spacecraft captured the first of three high-resolution sequences, this one near the terminator as a ridealong with CIRS. The westernmost image shows the deep, angular, relatively fresh crater visible near the center of the crescent mosaic. It features lobate landslide flows and a few sharp linear grooves. These were the closest views of the encounter, at roughly 8600 km. A simultaneous wide angle frame is used for context. Gorgeous detail!

ISS_049RH_HIRESMAP001_CIRS:

Posted by: volcanopele Aug 28 2008, 04:20 AM

Very nice! I have to admit, I didn't pay much attention to this encounter, so it is nice to see something done with these.

Posted by: Exploitcorporations Aug 28 2008, 04:30 AM

Possibly the highlight of the encounter, the huge 14-footprint mosaic and stereo views of the very prominent (and hopefully soon to be named) ray crater are truly astonishing. This may be one of the best observations of the PM, and nicely compliments the single frame of it accquired during the previous close pass in November 2005. Here's the eleven shots comprising the mosaic portion of this sequence. Keep in mind that limitations imposed by: a)software and : exploitcorporations' alcohol consumption results in distortions of perspective and position. I take no responsibility for you getting lost and your oxygen bottle running out.

ISS_049RH_HIGHRES001_PRIME

Posted by: Exploitcorporations Aug 28 2008, 04:34 AM

Thanks, VP! I had the sinking feeling that much of this would never see the light of day, and they're such nicely done sequences. ISS deserves another batch of cookies.

Posted by: Exploitcorporations Aug 28 2008, 04:47 AM

Here's poster showcasing all the currently available products from this flyby with *&%#@(!!) Ray Crater in view. I stole ugordan's fantastic distant color rendition from his flickr page. (psssst....I'd like to see that whole mosaic in color sometime. If anyone can do it, it's you.) The closeup view in the upper right corner begs a few questions...."Is all that powdery craterless freshness landslides? What's up with that peppering of tiny craters near the central peak? Are those layers in them thar walls?"
On that note, where does the time go?

Posted by: Exploitcorporations Aug 28 2008, 05:00 AM

The last of the three high resolution observations was taken at roughly 25.000 km. It's a south-to-north transect of a region just to the southeast of the unnamed basin adjacent to Tirawa (whew...you're probably just ast lost as I usually am after that).
Wherever that happens to be, the southermost (bottom) frame has what might be a spectacular crater chain or graben. I'll bet on the latter. Two images from the global mosiac are included to the left for context.

ISS_049RH_HIGHRES001_PRIME (part 2)

Posted by: elakdawalla Aug 28 2008, 05:09 AM

I don't know if it's ironic, hilarious, troubling, or deeply, deeply sad that I read the above at 10 pm in an at least slightly inebriated condition, after the consumption of three cocktails...

I guess drinking and mosaicking is OK, EC, because this is great work. You've inspired me to get back to the updating and reformatting of my satellite pages. Workin' on Dione as I type. EDIT: http://planetary.org/data/cassini/dione.html.

--Emily

Posted by: Exploitcorporations Aug 28 2008, 05:21 AM

Just a few odds and ends before I sign out...too tired (ahem) to finish up the parting global mosaic. Yeah, the one with Saturn's big yellow butt in the background. I hereby throw down ye olde gauntlet to ugordan to complete or collaborate on That Thing. If the backdrop is somewhat consistent, it would be freaking stunning. A clear filter version should be posted here soon.

Sorry for being lazy/absent/ugly/electrocuted/ect. I lurk religiously and post stingily. Except for today.

For Doug and admins: (Politics, politics, politics {urp}, politics, politics, random pop-culture reference, image, politics, image, politics, politics, BLEEEARGGGHHH!!!, pentinence....{hiccup}, politics. And thanks for running the forum. Yes, I will get an image hosting account somewhere.

There's a scarp in the middle of it all.

Posted by: Exploitcorporations Aug 28 2008, 05:31 AM

WOOHOOO!!!!. I vote for all of the above. I hope they were competent cocktails. Dione and I are headed down to the Crescent for Karaoke Assault Squad and "Why Did You Bring that 1100km-Diameter Iceball Into Our Bar?" Night. Regardless, (don't?) drive safely, and I need to find pants. Poof.

Posted by: volcanopele Aug 28 2008, 05:48 AM

Now don't go mixing politics with image processing. That's worse than alcohol and image processing. Next thing you know, you'll be etching your preferred candidate's name in your image products.

Now don't all go looking at my recent Enceladus products...

Posted by: Stu Aug 28 2008, 05:52 AM

After all the "technical hitches" during the UStream chat, I'm frankly amazed you limited yourself to just 3 drinks..!! ( It went very well though, eventually, another good show, well done. )

Posted by: Exploitcorporations Aug 28 2008, 06:10 AM

He's late, again. I'll tear myself away from waiting long enough to state that there's a teensy tiny Peter Kropotkin lodged inside Izanami basin. (PS: he's almost as dead as Rhea) Pffff...your Enceladus products are merely accurate, beautiful, and scientifically useful distractions from both my beer and my caffeine-fueled and morally superior DIY Enceladus finger paintings. I will now crawl off and yell at the cat.

Posted by: dvandorn Aug 28 2008, 06:27 AM

Ya know, EC... back when the forum was deciding (in some poll or another) that Rhea was undoubtedly the most boring single object in the Solar System, I vehemently disagreed, noting many of the features you're pointing out in these excellent images. Especially the massive proliferation of what are either endogenously-controlled graben or exogenously-controlled crater chains.

Thank you very much for bringing into focus this quite fascinating satellite.



-the other Doug

Posted by: volcanopele Aug 28 2008, 07:15 AM

It is still the most boring moon in the solar system (that meets the spherical requirement for being a planet). But no one says that boring can't have some beauty to it.

Posted by: Mariner9 Aug 28 2008, 10:45 AM

My vote for the single most boring object in the solar system is a tie between Dr. Phil and Regis Philbin.

In third place, Rhea is the solid contender.

That being said, these mosaics are beautiful. Especially the rayed crater. Thanks for processing these and sharing.

Posted by: tedstryk Aug 28 2008, 11:35 AM

Wow, strange coincidences. After too much beer, I almost posted to "inform" exploitcorporations that the images were of Rhea, not Dione...not sure why I was thinking Dione.

Posted by: belleraphon1 Aug 28 2008, 12:45 PM

Absolutely stunning, EC!!!!! As always.

Rhea is almost like the control blank for the Saturn system. Heavily pelted and now serene(?!) under all those scars.

Craig

Posted by: ugordan Aug 28 2008, 07:42 PM

Superb mosaics, Exploitcorporations!

I'm not sure I'll be doing the whole huge color mosaic soon, too many frames and Rhea rotates considerably during the one or so hour it took. Here's just one section in false color, contrast-stretched and I subdued the hues a bit. Removed the Saturn backdrop as perspective change between footprints caused registration problems.

http://farm4.static.flickr.com/3118/2806874356_bf8485d809_o.jpg

It looks pretty nice, even if I do say so myself. Rhea may be the most boring moon, but I prefer it over say Dione as it's actually got some nice brownish hue to it. Dione is greenish in false color; yuck!

Posted by: centsworth_II Aug 28 2008, 08:56 PM

Posted by: stevesliva Aug 28 2008, 09:36 PM

Some massive settling on the left post-impact means fewer secondary impact craters than on the right?

Posted by: ugordan Aug 28 2008, 10:17 PM

Speaking of impact deposits, did anyone take note of a string of dark stains seen vertical (splitting the mosaic right in half) in my above composite? Here's a crop and enhancement at the original geometry, equator is roughy horizontal:

They're very faint, but are black-ish unlike the rest of Rhean regolith. Apparently they can only be seen in lower phase imagery due to very low contrast. Do we know of a crater whose ejecta might have produced this (although ejecta on Rhea seems brighter than the surroundings) or could this have something to do with the hypothesized ring? I found the equatorial orientation somewhat interesting, otherwise I'd pay no attention to this.

Posted by: ElkGroveDan Aug 28 2008, 10:20 PM

It has the appearance of a massive landslide or escarpment.

Posted by: stevesliva Aug 28 2008, 11:05 PM

Very very interesting. So this obviously can't be Rhea. I don't really see deposits like that forming linear features in other directions.

Posted by: Exploitcorporations Aug 28 2008, 11:38 PM

Here's the parting global mosaic , with the poorly registering Saturn backdrop replaced. 24 clear filtered images are used, with one WAC image plugging gaps in the western limb.

ISS_049RH_REGMAP001_PRIME:

Posted by: jasedm Aug 29 2008, 08:14 AM

^ Magnificent!
I've often felt slightly guilty at vicariously enjoying the fantastic image products showcased here, so I've recently bought Photoshop and am slowly teaching myself the basics - hopefully I'll be able to post some mosaics myself at some stage.

Ugordan - very intriguing dark markings near Rhea's equator (and well-spotted once again), it would be interesting to see how closely they match with the supposed orientation of any ring material.
There seems to be a large amount of dark material in the Saturn system (Phoebe, Iapetus, and at the bottom of craters on Hyperion, Janus and Epimetheus, to say nothing of regional differences on Dione and Tethys) I wonder how similar the material is spectroscopically?

Posted by: tasp Aug 29 2008, 01:42 PM

The Gehrels Asteroid book indicates the Iapetan dark stuff is quite similar to D type asteroid spectra.

IIRC, we also have Cassini data indicating the Hyperion and Iapetan dark stuffs are quite similar to each other.

Also note, the Iapetan dark stuff shows a visual subtle color shift going from east to west (or west to east if you think about it).

To me, the color shift is kind of a problem for the folks theorizing the dark stuff is evaporative residue. Particularly if there is a mechanism for an externally sourced dark material that might sequentially apply (react?) longitudinally in synchrony with Iapetus' position around Saturn.

Posted by: hendric Aug 29 2008, 08:01 PM

We've been missing you. Now get over to the HAPS thread pronto.

Posted by: ugordan Aug 30 2008, 11:02 PM

I know I said I wouldn't be doing the color mosaic soon, but seeing EC's great version made me try it myself after all. Here it is in false colors (though I fiddled with color balance so it's false false color) and with Saturn removed (8.5 megabytes):

http://farm4.static.flickr.com/3015/2812507296_1e0517ed67_o.jpg

Also, color (but contrast stretched) view of the "splat" crater:
http://farm4.static.flickr.com/3012/2810255909_e1d30140eb_o.jpg

And I might as well throw in an old Kodak moment of a sort, from the November 2005 flyby:
http://farm4.static.flickr.com/3249/2807213084_dd64ff28d1_o.png

Posted by: tedstryk Aug 31 2008, 01:10 PM

Beautiful! But since a double negative equals a positive, doesn't that mean it's true color?

Posted by: Exploitcorporations Sep 3 2008, 07:34 AM

*&%#$@in' amazing, Gordan! You have no idea how many times I've premptively edited posts (or avoided making them altogether) to avoid the expletive-induced banhammer on account of your work. I did a preliminary overlay of your color product with my fake Saturn backdrop (derived from your WAC composite from the same flyby) and the western dark sliver of the mosaic from my attempt, and the alignment is decent. Mind if I post the hybrid in a few days?

That equatorial band looks prominent and very real in stretching this image.

Posted by: ugordan Sep 3 2008, 08:16 AM

You're too kind, EC. By all means go ahead with combining the two views, I'm eager to see how that turns out!

I agree the equatorial "band" (dark patch string might be a better term actually) can be seen stretching quite a long way across the disc. Very interesting. It's virtually invisible in a RGB view showing the same hemisphere, but at lower phase angle taken in November 2005: http://farm4.static.flickr.com/3179/2814380945_d25ee27152_o.jpg .
Photoshop's rescaling algorithms leave a lot to be desired, the top left mosaic footprint is noticeably blurred compared to others as any, even the least bit of scaling further blurs the image. That particular footprint for example was scaled twice (alignment issues), unlike others which were scaled just one time.