[X] My Assistant

[djellison]

The moon on the left moved a lot during the three images this was done with - so it was a big of a botch-job to create that, but I really like it

Doug

[mhoward]

The moon on the left moved a lot during the three images this was done with - so it was a big of a botch-job to create that, but I really like it

That is absolutely the craziest Cassini image yet... seems like they just keep getting crazier.

[Bill Harris]

Absolutely beautiful. The moon on the left has a blusih tint. Interesting that the rings have a fuzzied outline. How close are we to the plane of the rings? I suspect that we are at a slight angle so we are seeing the near and far edge of the rings and not a fuzzy thickness.

--Bill

[chris]

Doug,

have you got a bigger version of that image? I see my new desktop.....

Chris

[djellison]

Nope - that is as big as it gets. They were 1024 x 1024 obviosuly, but that's simply a crop from that - there's just black around the outside

I actually resized it 200% to better align the channels, then resize back down to the size you see there - but that's all there is imagesize wize.

Doug

[chris]

But the 1024 x 1024 version would still have the rings all the way across...

[djellison]

Told you we might drop a few posts on the way in the move.... it's a bit slow at the moment but that should improve





Doug

[David]

Those are, left to right, Rhea, Dione, and Mimas, right?

[djellison]

Those are, left to right, Rhea, Dione, and Mimas, right?

Dont look at me - I havnt got a clue

Doug

[ilbasso]

Yes, that's what the NASA website says.

[dilo]

Here an interesting steregram of Saturn+Ring (crossed eyes, start images are W00005976 and 5989):

[RedSky]

Its been almost a year now of Cassini Saturn images (approach & post SOI), and I keep thinking I've missed something...

While many of the ring & moon images are truly breathtaking... I don't recall seeing anything mentioned at the press conferences or on the Cassini web site regarding those "dark radial ring spokes" that were discovered during the Voyager flybys. The initial mystery was that any radial feature in the rings should be quickly spread out by the differential rotation rates between the inner portion orbiting faster than the outer region. I know the thinking now is that they were produced by dust above the ring plane held in the magnetic field.

Has anyone heard any news about them from Cassini, let alone any images?

RedSky

[tedstryk]

From what I have read, that is because they have been absent. There has been some speculation that this is due to the high tilt of the ring plane toward the sun right now. As Saturn moves increasingly toward an edge on configuration, it will be interesting to see if the spokes seen by Voyager and HST reappear.

[Guest_Sunspot_*]

The rings are back in view now :

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=36561

[Guest_Sunspot_*]

Bizzare patterns in the F Ring/Prometheus and Pandora:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=37451

[cIclops]

Bizzare patterns in the F Ring/Prometheus and Pandora:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=37451

That's not bizzare, its merely a couple of aliens playing a game of pong with the F ring.

[dilo]

Bizzare patterns in the F Ring/Prometheus and Pandora:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=37451

That's not bizzare, its merely a couple of aliens playing a game of pong with the F ring.

This is enhanced version, clearly showing wath should be the mechanism of fabrication of "density waves" in the F ring:

In fact, image was taken immediately after alignment between Pandora and Prometheus (the two super-exposed spots outside and inside the ring, respectively).
Combined tidal pull from the two moons creates a void in the inner part of the F ring, which then evolve in a spiral structure due to differential rotation.
The other two spiral strucutres visible in the lower portion if this image and more evident other imoages from this sequence (like http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=37522),
are "fossils" from previous alignment events, which should occour every abot 39 rotations of ring-F material (about every 24 days) and should be separated by 9 degree each other.
This is another great example of the incredible gravitational Luna Park offered by Saturn system! I would like to simulate these formations, anyone expert of n-body simulations?
Marco.

[paxdan]

Looks like they shot an F ring movie. Looking forward to the ani-gif or QT movie.

[dilo]

Looks like they shot an F ring movie. Looking forward to the ani-gif or QT movie.

Yes, is a long "film" but there are some time "holes"...
Anyway, here a couple of short sub-sequences (click to see animation):

[paxdan]

Cheers Dilo.

[dilo]

Do someone can explain real nature of structures visible in this image? I'm referring to "waves" in the inner limit of the gap:
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00033700.jpg
Are they real density waves or simply image/sensor artifacts (like aliasing)...?
they are visible only in the right portion of previous image:
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00033699.jpg
and seems to disappear in the next one:
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00033768.jpg
moreover, last image is a little bit disappointing, it seems truncated in the lower portion...

[volcanopele]

Do someone can explain real nature of structures visible in this image? I'm referring to "waves" in the inner limit of the gap:
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00033700.jpg
Are they real density waves or simply image/sensor artifacts (like aliasing)...?
they are visible only in the right portion of previous image:
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00033699.jpg
and seems to disappear in the next one:
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00033768.jpg
moreover, last image is a little bit disappointing, it seems truncated in the lower portion...

Unfortunately, the images on the JPL Raw images no longer represent all the images being returned. For example, the images you point to was part of a sequence with 250 images and more. So the image that explains what causes those waves isn't in there. I don't think this is deliberate, but is annoying. Not sure who at JPL I need to pester to fix this. We use the JPL raw images page to point to our images out side the team, or when we are at home and can't use the internal mechanism.

So there is an explaination....

[Bjorn Jonsson]

Well, hopefully someone gets pestered so this gets fixed soon. This is an extremely frustrating problem. For example I'd love to see the 32 missing images of Mimas. And hopefully at least some of the new Tethys images show up.

[alan]

Do someone can explain real nature of structures visible in this image? I'm referring to "waves" in the inner limit of the gap:
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00033700.jpg
Are they real density waves or simply image/sensor artifacts (like aliasing)...?
they are visible only in the right portion of previous image:
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00033699.jpg
and seems to disappear in the next one:
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00033768.jpg
moreover, last image is a little bit disappointing, it seems truncated in the lower portion...

I'll give this a try: There is a moon orbiting in the gap ( I don't remember its name right now) it orbit is slightly elliptical. When it makes its closest approach to the ring the tides caused by its gravity makes a little dent. Its orbital period nearly matches so you get a series of dents, one from each close approach, which slowly smear out.

[volcanopele]

I'll give this a try: There is a moon orbiting in the gap ( I don't remember its name right now) it orbit is slightly elliptical. When it makes its closest approach to the ring the tides caused by its gravity makes a little dent. Its orbital period nearly matches so you get a series of dents, one from each close approach, which slowly smear out.

You're thinking of the Encke Gap and Pan:
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=39038
The Encke gap is at top. near the outer edge of the A ring is the Keeler Gap, which is what Dilo is pointing to. However, prior observations of the Keeler Gap have led to speculation that the Keeler Gap may also be tended by a so-far undiscovered moon:
http://ciclops.lpl.arizona.edu/view.php?id=867
The waves seen in these latest images appear to be similar to those seen on the inner edge of the Encke Gap shortly after SOI:
http://ciclops.lpl.arizona.edu/view.php?id=248
again suggesting that an unseen moon is in the Keeler gap.

[Guest_Sunspot_*]

So some of the more interesting images are being withheld from public release?

[Decepticon]

So some of the more interesting images are being withheld from public release?

Welcome to JPL.

[volcanopele]

So some of the more interesting images are being withheld from public release?

I don't think it was intentional, I think they just have a bug in the program they are using to get the images from the feed. This started in mid-April and hasn't been fixed yet...

In case you are wondering, even I haven't seen the latest Tethys images so there doesn't appear to be anything wrong there, yet...

[Guest_Sunspot_*]

Warped F Ring:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=39871

Looks like it's part of a time lapse sequence too.

[alan]

Twelve new moons discovered around Saturn

"Astronomers have spotted 12 tiny new moons circling Saturn. The observations could help scientists understand how such satellites become snagged by gas giants.

A team of astronomers from the University of Hawaii and the Carnegie Institute of Washington first spotted the dozen using the Subaru telescope on Mauna Kea, Hawaii on 12 December 2004. Their observations were part of a broader hunt for irregular moons - so-called because their orbit is far from circular or highly inclined with respect to their planet’s equatorial plane.

They made follow-up observations from January to March 2005 with the Keck Telescope, Gemini North and Subaru and reported their results to a mailing list on Tuesday.

The new finds double the number of irregular moons orbiting Saturn and brings the total to 46. Eleven of the 12 new moons orbit in a retrograde orbit - opposite to the rotation of the planet."

http://www.newscientist.com/article.ns?id=dn7344

[Bjorn Jonsson]

Still no images of Tethys (I wonder if they are on the ground now) but some new images of the rings - however, I think there should be more. If the Tethys images do not show up, assuming they were received we may not see them until several weeks from now (at the CICLOPS site) or even not until a year from now (at the PDS)

[volcanopele]

Still no images of Tethys (I wonder if they are on the ground now) but some new images of the rings - however, I think there should be more. If the Tethys images do not show up, assuming they were received we may not see them until several weeks from now (at the CICLOPS site) or even not until a year from now (at the PDS) 

Ummm, they are not on the ground yet... I'm getting concerned.

[Guest_Sunspot_*]

Maybe they didnt take any pictures after all....... I believe these orbits are designed to study the rings?

[dilo]

Warped F Ring:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=39871

Looks like it's part of a time lapse sequence too.

Then a small movie (cannot resist!) - click to see animation! :

[volcanopele]

You're thinking of the Encke Gap and Pan:
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=39038
The Encke gap is at top.  near the outer edge of the A ring is the Keeler Gap, which is what Dilo is pointing to.  However, prior observations of the Keeler Gap have led to speculation that the Keeler Gap may also be tended by a so-far undiscovered moon:
http://ciclops.lpl.arizona.edu/view.php?id=867
The waves seen in these latest images appear to be similar to those seen on the inner edge of the Encke Gap shortly after SOI:
http://ciclops.lpl.arizona.edu/view.php?id=248
again suggesting that an unseen moon is in the Keeler gap.

Expect something on this today....

EDIT: Okay, maybe not today. Maybe Monday. JPL

[Guest_Sunspot_*]

Hyperion again: http://ciclops.lpl.arizona.edu/view.php?id=971

Can't wait to see it up close.

[dilo]

Two wonderful Saturn images taken on May 04, 2005 from approximately 1.2 MKm.
Thi is a rgb "real color" combination:

and this a M3 (methan filter) mosaic:

enjoy!

[volcanopele]

Expect something on this today....

EDIT: Okay, maybe not today.  Maybe Monday.  JPL   

I thought this delay was because of the IAU Circular needed to announced S/ 2005 S 1, but now I see that this delay is once again caused by JPL.

BTW, the IAU Circular 8524 on May 6th announced S/ 2005 S 1. Don't have the text of this yet. If anyone does, please post it here. The IAU Circular page is back up (though you still need a password to read the circulars, http://cfa-www.harvard.edu/iauc/RecentIAUCs.html ).

Info I can say because I am sure it is in the circular is that S/ 2005 S 1 is a newly discovered satellite of Saturn discovered by Cassini ISS. This new satellite, ~7.5 km across, was first found on May 1. S/ 2005 S 1 is located within the Keeler Gap of the outer A ring.

[The Singing Badg...]

C. C. Porco, CICLOPS, Space Science Institute, Boulder; and the Cassini Imaging Science Team report the discovery of a new satellite of Saturn, designated S/2005 S 1, orbiting within the Keeler gap in Saturn's outer A ring. (The object had been previously inferred from the presence of features observed on the outer edge of the Keeler gap; cf. Porco et al. 2005, Science 307, 1226, Fig. 10). The object was discovered in six images taken over 16 min on May 1 from a time-lapse sequence of 0.180-s narrow-angle-camera exposures that were targeted to the illuminated side of the outer edge of the A ring (with phase angle about 33 deg and image scale 6.9 km/pixel). S/2005 S 1 was subsequently found in 32 (7 km/pixel) low-phase images taken of the F ring on Apr. 13 (spanning 18 min) and again in two high-resolution (3.54 km/pixel) low-phase images taken on May 2, when its 7-km disk was resolved. The satellite orbits Saturn every 0.594 day at a distance of 136500 km. The estimated geometric albedo is 0.5. The data are too coarse to yield any statistically significant orbital eccentricity or inclination.

[alan]

S/2005 S 1 was subsequently found in 32 (7 km/pixel) low-phase images taken of the F ring on Apr. 13 (spanning 18 min)

Is this it?
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00031664.jpg
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00031659.jpg
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00031656.jpg
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00031653.jpg

[volcanopele]

Is this it?
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00031664.jpg
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00031659.jpg
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00031656.jpg
http://saturn.jpl.nasa.gov/multimedia/imag...0/N00031653.jpg

Yep, that's it. Hopefully some better views will be released this week. It better.

I will put together something tomorrow morning on my blog now that I know how far I can go.

[alan]

It seems rather obvious in those images, why wasn't it discovered then instead of on May 1? Did everyone assume it was Pan like I did at first when looking for it in those images?

[tedstryk]

So what is the holdup with this release? Images were certainly released sooner after other flybys? Is there some sort of discovery or important finding (besides this new moon), or is it just a "run of the mill" image release?

[volcanopele]

It seems rather obvious in those images, why wasn't it discovered then instead of on May 1? Did everyone assume it was Pan like I did at first when looking for it in those images?

It is a rather small moon. Most likely we are now just starting to stare at the rings for a long enough time span with high enough resolution in order to observe this moon.

As noted earlier, this moon is not completely unexpected.

[volcanopele]

So what is the holdup with this release?  Images were certainly released sooner after other flybys?  Is there some sort of discovery or important finding (besides this new moon), or is it just a "run of the mill" image release?

Well, as I said earlier, I thought the hold up was the IAU Circular which would need to announce the new moon first. But now I suspect it is just JPL. Unfortunately, I have very little connections with the small satellite portion of the team, and only really care about these little guys when one is discovered or we starting seeing surface features (a la Phoebe or Epimetheus).

[Guest_Sunspot_*]

it might be a problem with the JPL RAW site...there's very little being posted at all at the moment (maybe they just aren't taking many pics at the moment), but some of the links to the pictures are broken too.

[volcanopele]

it might be a problem with the JPL RAW site...there's very little being posted at all at the moment (maybe they just aren't taking many pics at the moment), but some of the links to the pictures are broken too.

This has nothing to do with the RAW images, this is about the image release...

[Guest_BruceMoomaw_*]

A major new find, just announced on Jason's blog: Cassini has found the tiny moon responsible for the Keeler Gap:
http://volcanopele.blogspot.com/2005/05/ne...te-s-2005-s-1.h
tml .

Just as with Pan in the Encke Gap, they were confident it was there on the grounds of indirect observations of its gravity wake in the Gap's edges -- and, sure enough, here it is.

[Guest_BruceMoomaw_*]

Let's try that URL again:

http://volcanopele.blogspot.com/2005/05/ne...s-2005-s-1.html

[Guest_BruceMoomaw_*]

OK, let's try it a third time:

http://volcanopele.blogspot.com/2005/05/ne...s-2005-s-1.html

[volcanopele]

A major new find, just announced on Jason's blog: Cassini has found the tiny moon responsible for the Keeler Gap:
http://volcanopele.blogspot.com/2005/05/ne...te-s-2005-s-1.h
tml . 

Just as with Pan in the Encke Gap, they were confident it was there on the grounds of indirect observations of its gravity wake in the Gap's edges -- and, sure enough, here it is.

This is what has been discussed on this thread the last day or so. That post is based on Singing Badger's post of the IAU Cicrular and based what I could off of that.

[dilo]

It seems rather obvious in those images, why wasn't it discovered then instead of on May 1? Did everyone assume it was Pan like I did at first when looking for it in those images?

Great finding, Alan! I rimember these images taken almost 20 days ago; they belongs to a long sequence and I commented them on this thread (see http://www.unmannedspaceflight.com/index.p...dpost&p=8583)... However, I didn't noticed the moon, even if rather obvious, in fact
Anyway, based on these images, I made a little movie clearly showing the movement of the moon inside keeler Gap:

[Guest_BruceMoomaw_*]

Well, that's what I get for not monitoring all the threads properly.

[alan]

It seems rather obvious in those images, why wasn't it discovered then instead of on May 1? Did everyone assume it was Pan like I did at first when looking for it in those images?

Great finding, Alan! I rimember these images taken almost 20 days ago; they belongs to a long sequence and I commented them on this thread (see http://www.unmannedspaceflight.com/index.p...dpost&p=8583)... However, I didn't noticed the moon, even if rather obvious, in fact
Anyway, based on these images, I made a little movie clearly showing the movement of the moon inside keeler Gap:

I remembered the movie you made three weeks ago when I was looking for those image. I was thinking about how close it came to being discovered by an amatuer. Actually I remember seeing it back then (thinking thats just Pan, nothing to see here) and moving on to the next image because I was more interested in seeing Prometheus and Pandora.

[dilo]

I remembered the movie you made three weeks ago when I was looking for those image. I was thinking about how close it came to being discovered by an amatuer. Actually I remember seeing it back then (thinking thats just Pan, nothing to see here) and moving on to the next image because I was more interested in seeing Prometheus and Pandora.

Yes, about the same for me... maybe sometime we have too much informations in so few time, and we discard important things!
regards

[dilo]

Hey, guys, someone noticed this smaller object in the gap???

Yes, I know, could be sensor hotpixel, cosmic ray or even background star... but it seems to generate a secondary pattern of waves...
Jason, wath do tou think?

[alan]

It only shows up in one frame of the movie and there are no ripples on outside of the gap near it, probably a cosmic ray. I saw a few of these yesterday when I was looking for moons in images from last year, often in interesting places like in the cassini division, but none of them showed up in more than one image.

[dilo]

It only shows up in one frame of the movie and there are no ripples on outside of the gap near it, probably a cosmic ray. I saw a few of these yesterday when I was looking for moons in images from last year, often in interesting places like in the cassini division, but none of them showed up in more than one image.

Thanks alan... hey, my impression is that a furious amateur moon search is starting here!!!

[RedSky]

In this long exposure, there is a very faint ring well out (to the left) of the main rings.

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=40944


Is that the G or E ring? Also, while it may just be a background star shining through, it almost looks like a clump (tiny moon?) embedded in that faint ring (at about the 8 o'clock position... lower left... from the very brightly overexposed moon just below the main rings.)

Also, I've noticed that these very long exposures tend to have broad extensions of light eminating out from the overexposed rings. Is that just some sort of lens flare, glare, or optical artifact.... or is it physical? (i.e., reflections of dust orbiting around Saturn far out, such as the dust in the plane of the solar system causes the zodiacal light.)

RedSky

[um3k]

I believe that is the G ring, RedSky.

[dilo]

I believe that is the G ring, RedSky.

I think too. Herebelow an amazing animation of these super-exposed frames:
[img=http://img240.echo.cx/img240/5769/gring8pn.gif]
You can easily see Mimas and Janus (or Epimetheus) orbiting outside and inside it; in the last frames, also Prometheus is visible...

[DDAVIS]

A color study of the rings being refracted by the blue limb of Saturn from recent images:

http://www.donaldedavis.com/2005%20new/BENTRINGS.jpg

[dilo]

Great, it is a colorized image or a real multi-filter combination?

[DDAVIS]

[quote=dilo,Jun 16 2005, 02:01 AM]
Great, it is a colorized image or a real multi-filter combination?


It is an RGB image, although I had to artistically fill in parts of two of the channels as the images were offset somewhat.

Don

[dilo]

  It is an RGB image, although I had to artistically fill in parts of two of the channels as the images were offset somewhat.

Managed in order to obtain more realistic colors, hope you like!

[DDAVIS]

[quote=dilo,Jun 17 2005, 06:19 AM]
Managed in order to obtain more realistic colors, hope you like!

If you examine the original blue channel of my Saturn RGB try, located at:
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=41651

you will find Saturn is brighter than the other color channel images of that view in the preceding frames. The rings provide a brownish gray reference so the colors I used might not be too far off, although the saturation and contrast need work before I would dare commit to calling it a try at a naked eye view. Numerous color images show a blue limb darkening on Saturn, and much of the planets northern hemisphere seems to appear fairly blue in between the ring shadows. This appears to be a narrow angle view showing the 'blue sky' of the upper atmosphere of Saturn along the limb.

Don

[djellison]

I found some interesting image sets recently - but had to make do with red green violet - the results are quite pleasing though.. This is a composite of two frames, for some reason they did it in three frames - but the middle one is totally redundant as far as I can tell.



http://www.unmannedspaceflight.com/doug_im.../sat_jun_05.jpg 64kb

Doug

[Bill Harris]

At first I suspected that the blue limb on Saturn was due to methane in the atmosphere, but now I'm thinking that it is due to aersol scattering in the clear upper atmosphere. I wonder if the blue area around the ring shadows is be due to cooling of the atmosphere and increased aerosols because the rings block whatever solar heating happens there?

--Bill

[dilo]

Last sequence of Cassini division show an intriguing variation in outer limit of A ring:
http://img76.echo.cx/img76/4820/cassinidivision5ly.gif

[volcanopele]

Rings are definitely NOT my speciality, but maybe the inner edge of the A ring is a eccentric, rather than circular?

[Guest_BruceMoomaw_*]

Voyager found at least 2 eccentric rings -- and I believe one of them WAS on the inner edge of the B Ring (which I think was what Dilo meant). I'll have to recheck this, though.

[Guest_BruceMoomaw_*]

Make that "the OUTER edge of the B Ring" -- that is, the inner edge of the Cassini Division.

[volcanopele]

See what I mean. I couldn't even tell if that was the inner edge of the A ring or the outer edge of the B ring... But still, eccentricity in the ring might be the cause

[dilo]

Yes, Jason, this should be the geometric explaination... (hey, we were both wrong about denomination! variation occour in the outer B ring edge! ).
But wath about mechanism originating eccentricity? The odd thing is that this variation do not appear in any other structure, even very close to this one...
Maybe explaination is the resonance 2:1 with Mimas, which exhibit some orbit eccentricity and can introduce this asymmetry. Or, more probably, is the combined resonance with Mimas + Tehys (4:1, more massive but circular orbit) which should introduce a mareal effect...
Who knows? (hey, should be funny to simulate this stuff!...)

[dilo]

Incredibly clear Saturn night side thanks to reverberated light from rings:
http://saturn.jpl.nasa.gov/multimedia/imag...2/W00008416.jpg
http://saturn.jpl.nasa.gov/multimedia/imag...2/W00008400.jpg

[Jyril]

In this image ringshine makes Saturn look almost shiny. Weird.

http://saturn.jpl.nasa.gov/multimedia/imag...2/W00008589.jpg

[JRehling]

In this image ringshine makes Saturn look almost shiny. Weird.

http://saturn.jpl.nasa.gov/multimedia/imag...2/W00008589.jpg

That's an interesting comment. There's some interesting math behind the explanation (which I'm contemplating hand-waving-style in my head instead of writing down). "Shiny" is the description of a "specular" (or mirror-like) surface, which reflects incoming light out at an angle reflected over the line perpendicular to the tangent plane (eg, billard ball -style bounces only). Lambertian surfaces scatter light completely in all directions (cardboard is pretty Lambertian; cotton more so). Every surface is somewhere on the scale between the two; you can probably count on clouds, like Saturn's, being highly Lambertian. Here, the lighting source is bizarre; the lit topside of the rings are visible over half of Saturn only, and the light incident to Saturn's surface from that ends up producing a spot of light similar to what you'd see on a specular surface that was lit uniformly.

I think it's an interesting area of applied mathematics to see when two different causes lead to highly similar physical effects -- should be its own field of study!

[Bjorn Jonsson]

This is not a specular reflection although it may look like it. What's happening is that there is a brightness minimum centered on the 'midnight longitude' due to Saturn's shadow on the rings. Also the brightness of the rings is strongly dependent on phase angle, thus further complicating matters and making things rather non-intuitive. There are some experimental computer simulations I did of this at http://www.mmedia.is/bjj/3dtest/index.html , including a simple cylindrical map showing the ringshine intensity for a solar elevation angle of 15 degrees above the ring plane.

[ilbasso]

Just saw this headline in the BBC news online: "Saturn rings have own atmosphere" - and it was discovered that the planet's rotation rate has slowed by 7 minutes since the Pioneer and Voyager visits. No news of this in the US media yet!!

Saturns rings have own atmosphere

Of course, there are other stories on the Beeb that don't make it into American press, either, like this one: Hedgehog numbers 'in nose-dive'

[alan]

The radio period is what has changed. It must not be as tightly controlled by the planets rotation as has been assumed. It doesn't seem possible that the rotation period of the entire planet has changed. Where would that much angular momentum go?

[volcanopele]

Just saw this headline in the BBC news online:  "Saturn rings have own atmosphere" - and it was discovered that the planet's rotation rate has slowed by 7 minutes since the Pioneer and Voyager visits.  No news of this in the US media yet!!

Saturns rings have own atmosphere

Of course, there are other stories on the Beeb that don't make it into American press, either, like this one:  Hedgehog numbers 'in nose-dive'

Both the ring "atmosphere" and the changed radio period of Saturn are old news stories, both nearly a year old.

The other one, on the hedgehogs, am I supposed to laugh or cry? I couldn't stop laugh regarding the tidy gardens comments.

[Rob Pinnegar]

Man, those English hedgehogs are in trouble.

Anyways: A while back we had a few posts in this thread regarding visibility of the G Ring in certain Cassini images. Here's another one along the same lines:

In the Raw Images section under "Telesto", the third image (as of July 2nd; the ID number is W00008506) seems to show a really, really faint crescent-shaped ring arc through the middle of the image -- it's so faint that it is only relatively easy to see on the thumbnail. The image was taken June 29th and the "openness" of the ring, in terms of angular distance out of the ring plane, seems to agree with images of the main ring taken at about the same time.

If it is a ring and not just some weirdly shaped "zero point" artifact, then presumably it is either the E ring or the G ring. It would be very interesting if it turned out to be the densest part of the E ring -- in all the E ring images I've seen, the ring only really seems visible when it is edge on. That in itself indicates that it might more likely be the G ring; but it doesn't seem to show the well defined inner rim that can be seen in some of the G ring images. (Of course, at that level of fuzziness, a sharp edge can't be expected to look like a sharp edge).

(Sometimes I really wish there was some optional program available at the Cassini site that could mark perpendicular distance from Saturn's rotational axis on these images -- particularly when dealing with narrow-angle shots of the rings. But I guess that, no matter how much stuff they put on the site, there will always be one more thing I'd like to see.)

[alan]

I got this from Saturn Viewer 2.5
http://pds-rings.seti.org/tools/viewer2_sat.html
time: 2005-JUN-28 03:20:00
viewpoint: Cassini
diagram center: Telesto
field of view: 1 ISS wide angle FOV
http://pds-rings.seti.org/work/viewer_sat_18376.jpg
E-ring is in the right spot, G-ring is at the right edge of the field
Perhaps volcanopele can confirm the time