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Posted by: ugordan Jan 18 2006, 07:08 PM

A great Rhea multispectral set recently came down, taken from a distance of around 245 000 km. Here's a RGB composite, Rhea really fills the NAC field of view in this one:

Posted by: Mariner9 Jan 18 2006, 10:55 PM

These RHEA images are great! Everyone please take note of the prominent geologic formations on the limb.

R-r-r-r-r-r-rhea's got R-r-r-r-r-r-r-ridges !!!!!!!!!!!!!!!!!!!!!!!

Correct me if I'm wrong, but this is the first direct confirmation that the "whispy streaks" on Rhea are similar to Dione's ice cliffs.

Posted by: Rob Pinnegar Jan 19 2006, 12:43 AM

Yeah. Good to finally see some evidence of SOME kind of activity on Rhea, even if it just be old grabens and some cracks.

Posted by: Steve G Jan 19 2006, 02:15 AM

I was wonderingif that old Voyager 1 picture showing the streaks was a practical joke!

Posted by: tedstryk Jan 19 2006, 02:43 AM

This image shows the cliffs very well. Unfortunately, it was a lone opnav while Voyager 1 was approaching, so super resolution is not possible.



Also, here is a sequence from Voyager 2. The images are shown in the order they were taken. Some are larger than others because when multiple frames were availabl, super resolution was applied. When they were not, images were shown at their size. But sequentially, they are in order. And as can be seen, the streaks become obvious as creacks as they approach the teminator.

http://img61.imageshack.us/my.php?image=v2rheaset5dp0xw.jpg

Posted by: David Jan 19 2006, 02:57 AM

What's the straight line slanting across the lower-left-hand quadrant? Surface feature or image artifact?

And doesn't Rhea have some pretty darn huge basins, even if they are in low relief?

Posted by: Michael Capobianco Jan 19 2006, 05:22 AM

Well, it's on both the Voyager image above and a number of Cassini images, so it's real enough. If the lines radiating from Cassandra on Dione are in fact scarps, as per http://www.planetary.brown.edu/m42/m42_68.pdf, it's not to difficult to imagine that this straight line is as well. But there are a number of straight lines on these moons, and not all of them can be explained that easily.

Michael

Posted by: ugordan Jan 19 2006, 08:21 AM

No, that's not an image artifact. A similar feature was seen in images taken months ago, see http://ciclops.org/view.php?id=745. I believe the feature itself is curved, but the viewing geometry makes it look straight. It's interesting that two different views produce a straight line, though I don't know if it's the same feature -- Rhea might have more than one of these linear features.

EDIT: On closer inspection, it turns out the above composite image and the CICLOPS release have a remarkably similar viewing geometry, that is, sub-spacecraft point. The only thing different is the illumination angle so it's not at all surprising the feature turned out to be straight in both images. Ted Stryk's larger image also shows the linear feature and due to a different viewing angle it's clear that it is in fact curved.
Talk about interesting coincidences...

Posted by: jmknapp Jan 30 2006, 12:53 PM

Does anyone know the three moons in this grouping:

http://saturn.jpl.nasa.gov/multimedia/images/raw/raw-images-details.cfm?feiImageID=62180



Rhea, Mimas & ????

Posted by: ugordan Jan 30 2006, 01:29 PM

Enceladus.
http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=605&vbody=-82&month=1&day=27&year=2006&hour=21&minute=45&fovmul=1&rfov=0.5&bfov=100 gives this result, obviously a couple of minutes after the Cassini image was taken.
Enceladus is the one more illuminated by saturnshine and farther from Rhea in that raw image.

On a side note, the http://ciclops.org/view.php?id=1761 shows a really perplexing trend in releasing only grayscale images when multispectral sets were obviously taken. There were a number of color composites ("natural" and enhanced color) by us amateurs a month ago and it doesn't really take more than 15 minutes to create such a composite. It's not like they have to be scientifically accurate, the imaging team clearly stated these images are for public purposes only anyway.
Why, then, the insisting on dull grayscale images? I know the moons are really bland in reality, but give me a monotone color image over a grayscale any time. It's as though the team are releasing these images against their will so they don't even bother with cool pics most of the time.
Not that there haven't been very spectacular releases, mind you! It's just that most of the time these releases tend to be routine-ish and hardly awe inspiring...

I'm sure I'll get bashed by volcanopele for this

Posted by: Fraggler Jan 31 2006, 11:01 PM

'Scientifically accurate' no, *calibrated* yes. Also when we ametuers put images together it's just that... CICLOPS has to draft captions and get those captions approved by NASA HQ.

There are also a lot more ametuers than there are image processors.

Posted by: JTN Feb 1 2006, 08:35 PM

http://saturn.jpl.nasa.gov/multimedia/images/index.cfm has some false-colour versions of recent icy-satellite releases where http://ciclops.org/ir_index.php?id=17 does not, for some reason. (There's no colour variant of the Rhea image you link to, but there is of one other Rhea image + two Dione images.)

Posted by: JTN Feb 1 2006, 09:27 PM

FWIW, here's a quick'n'dirty animation of the frames around this one (N00049532-N00049570).
(There are some earlier ones, N00049514-N00049531, but with them there'd be a jump in the animation.)

BTW, your http://www.unmannedspaceflight.com/index.php?showtopic=2158 does a http://cassinicam.com/isslookup/html/62180.html on these.

Posted by: volcanopele Feb 1 2006, 09:52 PM

Actually, the CICLOPS pages for those images have both the greyscale view and the false- or enhanced-color views for those releases that have both. Just click on the text link and not the image to bring up the caption and both views.

Posted by: ugordan Feb 1 2006, 10:06 PM

While you're here, can you tell us a ballpark figure on how long it takes to produce one such image? I'm referring only to image processing, not writing an advisory that has to get past NASAs PR office and stuff like that.
Just the actual image work?

Posted by: volcanopele Feb 1 2006, 10:10 PM

Depends on the image. I can only speak for my self, but typical mosaic of say Titan or Enceladus takes 1-2 days, barring any complications. For say a simple color composite (no fancy color map tricks that CICLOPS has been doing lately) for me takes 20-30 minutes. If I need to do any map projecting (which requires navigation/limb fitting of all the images involved), add 30 minutes-1 hour.

Posted by: jmknapp Feb 1 2006, 10:54 PM

Yeah, when I asked the question I hadn't finished that tool yet, & it wasn't reporting Enceladus due to a bug! (thanks, ugordan.)

Nice animation! Now that I got the simulated ISS viewer going, I'll try to make a smooth simulated animation of what the NAC saw during this mutual event. Should be interesting...

Posted by: ugordan Feb 2 2006, 08:34 AM

Outstanding work, Joe! You even simulate saturnshine (pretty accurately, too!). The only thing that comes to mind that would make your simulator even better would be a bit of antialiasing to remove the jaggedness of the limbs and textures, but it outclasses the JPL Solar System simulator already -- it doesn't do saturnshine.

A question, though -- there seems to be a slight shift in the predicted and observed positions in both your and JPL simulator. Is this due to the problem of calculating the exact time from a not-so-accurate distance (you mentioned this before, IIRC) or a problem in ephemerides?
I'd venture to say it's the former - I can't imagine Cassini coming to within 175 km of Enceladus with such prediction errors?

Posted by: jmknapp Feb 2 2006, 01:44 PM

I'm not sure where the shift originates from. Could be the uncertainty in the time, the ephemerides, the distance quoted on the raw image website, a programming bug or ???

The tool reports a time of 21:41:56 and there is a slight shift in position as you noted. If I set the time to 21:43:03 (67 seconds later), the images do line up pretty well:



If the boresight is shifted a little above, the images line up perfectly. I think there might be an issue where the boresight of the actual camera is not exactly in the center of the frame.

Setting the JPL SSS to that time gives a consistent picture:



I'll see what I might do about the aliasing.

EDIT: Here's a simulated animation of the event:

http://cassinicam.com/3moons.avi

Posted by: canis_minor Feb 3 2006, 05:12 AM

Here's a slightly less quick-and-dirty version of the three-moon mutual event.

Posted by: Bob Shaw Feb 3 2006, 01:10 PM

Very pretty!

Bob Shaw

Posted by: ljk4-1 Feb 24 2006, 03:49 PM

SATURN DAILY

- Rhea's Wisps In Color

http://www.spacedaily.com/reports/Rheas_Wisps_In_Color.html

Pasadena CA (SPX) Feb 23, 2006 - Bright, wispy markings stretch across a region
of darker terrain on Saturn's moon Rhea. In this extreme false-color view, the
roughly north-south fractures occur within strips of material (which appear
greenish here) that are a different color from the surrounding cratered
landscape.

- Fresh Features On Enceladus

http://www.spacedaily.com/reports/Fresh_Features_On_Enceladus.html

Posted by: ljk4-1 Apr 4 2006, 03:00 PM

SATURN DAILY

- Rhea And The Rings

http://www.spacedaily.com/reports/Rhea_And_The_Rings.html

Ithaca NY (SPX) Apr 1, 2006 - Saturn's crater-scarred moon Rhea floats in the
distance, peeking out from behind the giant planet's partly shadowed rings. This
view looks upward from just beneath the ring plane. The far side of the rings is
masked by Saturn's shadow. The north pole of Rhea is obscured by part of the A
ring and the sharply defined F ring.

- Cassini Reveals New Saturn Ring Features

http://www.spacedaily.com/reports/Cassini_Reveals_New_Saturn_Ring_Features.html