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Unmanned Spaceflight.com _ Cassini general discussion and science results _ Ring near edge on illumination

Posted by: Floyd Apr 11 2009, 01:21 PM

Not only are we seeing the long shadows of moons on the rings, but objects in the rings are now casting shadows. http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133374.jpgNotice the mini shadows on the bright twisted band just where the moon shadow ends.

One of you who is more adept at image cropping may want to post a cropped blowup.

Posted by: sci44 Apr 11 2009, 02:06 PM

Nice catch! You have just discovered 11,821 new moonlets!

(x2, rot 18 degrees, crop)



(Credit: NASA / JPL / SSI)

That ring seems to have many more large boulders than the others in frame - its amazing how chaotic it is.

Adjacent frames show the speed the long shadows move:
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133375.jpg

The large moon shadow here nicely maps out the shape/thickness of the rings:
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133376.jpg

The Cassini team are going to have fun finding classical names for all those moons.. smile.gif

Posted by: Ian R Apr 11 2009, 03:38 PM

Wow - is this the region periodically disturbed by the resonance with Mimas? That would certainly help explain the chaotic appearance of that ringlet. ohmy.gif

Posted by: scalbers Apr 11 2009, 03:42 PM

Pretty neat. They almost look like the shadow of a mountain range. Actually though are we seeing the shadows of ring irregularities instead? I would think the actual moonlets would usually be too small to resolve. Maybe we're seeing clumps of moonlets that are being warped away from the ring plane (or perhaps simply more dense than the surroundings).

Steve

Posted by: ugordan Apr 11 2009, 04:21 PM

Wow, that's seriously wicked. Nice catch, Floyd!

Posted by: ElkGroveDan Apr 11 2009, 04:37 PM

Thanks for catching that Floyd. This is amazing. I am utterly fascinated with ring particles and the subtle gravitational phenomena associated with so many distinct masses interacting.

I would think a careful examination of the elongated size and shape of those shadows would result in important data ripe for a new paper on particle size and density.

Posted by: sci44 Apr 11 2009, 06:18 PM

This is a rough attempt at an animation using frames N00133373.jpg, N00133374.jpg, N00133375.jpg

(http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133374.jpg etc)



(Credit: NASA / JPL / SSI)

There is a little movement in the shadows between frames, I was hoping for more.

Posted by: Floyd Apr 11 2009, 06:30 PM

Thanks sci44 for the crop and the movie. I am also surprised at how little the mini shadows change.

Posted by: helvick Apr 11 2009, 08:01 PM

It's not all that surprising if we assume that there is very little relative motion between the particles which I'd assume is generally the case unless there's a moonlet nearby disturbing things. Taking an 80000km altitude for the rings (which may be a bit off but it serves for general argument) - the orbital velocity of the particles is around 13km/sec. At that altitude 1 second of arc is remarkably close to 1km so you'd need almost 11 minutes between images to have the particles move by a degree along their orbit.

Posted by: dilo Apr 11 2009, 08:46 PM

Excellent finding, Floyd!

QUOTE (Ian R @ Apr 11 2009, 03:38 PM) *
Wow - is this the region periodically disturbed by the resonance with Mimas? That would certainly help explain the chaotic appearance of that ringlet. ohmy.gif

Ian, this is clearly the outer edge of B-ring, where particles are in 1:2 resonance with Mimas. The resonance causes Mimas' pulls on these ring particles to accumulate, destabilizing their orbits and leading to a sharp cutoff in ring density. These elevated structures could be eventually related to the relatively high inclination of Mimas orbit (1.57°) or to low velocity impacts in such dense region. Just two ideas...
It would be nice to have an estimated height of such features based on shadow lenght... any support on this?

Posted by: sci44 Apr 11 2009, 09:34 PM

Yes, an excellent find, Floyd!
The first frame of that anim is a bit out - I am sure one of the more experienced UMSF'ers can make a properly calibrated/cleaned up version..
Just watching that GIF - there is actually a trail of disturbance on the left third - from the edge of the ring cutting into the main ring plane - deeper as you go to the left - like the trail of something plowing into the ring at a very shallow angle? Strange. Are these large boulders, or loose collections of small particles? Electrostatic charges are said to play a role with structures like the ring-spokes - is that a factor here? I don't know..

By the way, the sequence of 14 (incrementally numbered) frames with the shadow of (Titan?) cutting across the rings, from
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133399.jpg
through to
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133412.jpg
is crying out for an animation - now if only there was an animator here.. smile.gif

Posted by: volcanopele Apr 11 2009, 11:01 PM

Most of the moon shadow stuff at the moment is either from Mimas or Tethys.

Very cool animations everyone!

Posted by: Astro0 Apr 12 2009, 06:42 AM

With Cassini's motion, this is not an easy set of images to register.
Here's my attempt at an animation.
Hard to see if any changes are 'real', 'imagined' or 'artifact'.



Posted by: nprev Apr 12 2009, 07:10 AM

All I got to say is WOW, you guys... blink.gif smile.gif

Astro, how many minutes does your animation span? (I'm thinking that it must be a fairly hefty period--15 min more or less?--given that moon shadow passing in & out of the FOV.) If that's true, then it's really striking how stable the "mountain silhouette" ring particle shadow pattern remains throughout the period.

Using the word "striking" because my gut feeling (and I'm probably not alone here) was that the rings' behavior must be pretty chaotic at the particle-level scale. That well may be, but not over as short a time scale as might be assumed. Should this be obvious in retrospect?

Just to blue-sky a bit, what if the "chaos threshold" is lower than we expect? By this I mean that perhaps the major ring particles (say 10m or larger) in at least this segment of the ring system have achieved some sort of dynamic equilibrium over time so that they really don't bounce around much relative to their neighbors. It sounds thin to me, too, but you'd think that the system would tend to evolve towards a low-energy state like that over time.

Posted by: ElkGroveDan Apr 12 2009, 07:31 AM

I would imagine that the Mimas/Tethys shadows(s) should provide a relative scale to calculate the sizes and the size distribution in that segment. The ratio of the diameter of Mimas to the triangle it's shadow creates should be the same as the ratio of these smaller objects. I wish I had the time to do this myself.

Posted by: Astro0 Apr 12 2009, 09:24 AM

nprev...not sure what time period. Someone here will be able to tell us I'm sure.

On the 'real' or 'imagined' question...
Take a look at this animation, looking at a small segment of larger version.



Right in the middle there seems to be some large 'particles' that tumble and I'm guessing that their corresponding shadows are also visible against the 'lit' ring structure in the background. Thoughts?

Posted by: Bjorn Jonsson Apr 12 2009, 01:26 PM

These images are amazing - I think they might be the most interesting images of the rings since SOI. Knowledge of the rings' 3D structure is about to be revolutionized. And let's not forget that these shadow will get much longer in the coming months.

Some quick 'back of the envelope' calculations: The solar elevation angle is ~1.9 degrees. Assuming that the shadows lie on a perfectly flat surface that is not tilted relative to Saturn's equatorial plane they are ~30 times longer than the height of the features that cause them. The length of the largest shadows is ~15 pixels. Assuming that the range is ~1.1 million km ("The camera was pointing toward SATURN-RINGS at approximately 1,138,888 kilometers away") and that Cassini is directly above the shadows (definitely not the case) the length of the shadow is ~100 km and the height of the feature casting the shadow ~3 km.

This is highly approximate but indicates that the highest 'peaks' are probably a few km high.

Posted by: Floyd Apr 12 2009, 01:50 PM

Ring dynamics are slightly beyond me (I'm a microbiologist), but if we think in terms of large boulders or small moons, and the boulder-boulder gravity interaction is small, then each is in its own eliptical orbit. So a boulder we see highest above the ring plane/with the longest shadow will drop down to the lowest point below the ring plane 180 degrees later. If one assumed that the boulders' phase and inclination are all random, then you would have the boulders all moving around relative to one another, but you would need to observe them through about 90 degrees of orbit to see really significant changes--and then the shadows would have rotated 90 degrees. So the question is, what size changes could you see in 45, 22.5, or 11.25 degrees of orbit? A shadow could at maximum shorten or lengthen by sine of the angle. Maybe 22.5 degrees is small enough to keep track of shadows and register images and big enough to measure changes.
Any of you with real knowedge of astrophysics/ring dynamics--please correct my physics I reasoning.

Posted by: ElkGroveDan Apr 12 2009, 02:57 PM

QUOTE (Astro0 @ Apr 12 2009, 02:24 AM) *
On the 'real' or 'imagined' question...
Take a look at this animation, looking at a small segment of larger version.
Right in the middle there seems to be some large 'particles' that tumble and I'm guessing that their corresponding shadows are also visible against the 'lit' ring structure in the background. Thoughts?


Astro0 I took the liberty of stabilizing your animated gif since I have found in the past (with one of Stu's originally) that the jumping around has a way of distracting from the actual changes.

A lot of it looks like it has to do with the lower resolving threshold of the optics interacting with the collector grid (or else the jpeg compression), but I do think I still see the "tumbling" effect on the larger particle right of center. It also might be a change of perspective among two or more visually aligned chunks, as the ring and Cassini pass each other. The full res images of this sequence whenever they are released will certainly be interesting.

 

Posted by: nprev Apr 12 2009, 06:02 PM

I agree, Dan. There are certainly relative motion & differential illumination effects at work in addition to the performance limitations of the optics, and it's very hard to tell what's "real" from this raw data other than the shadows.

Definitely looking forward to more!!! smile.gif

Posted by: Astro0 Apr 13 2009, 10:04 AM

Nice work Dan wink.gif

I hope that we can look forward to even better images like these.

If all continues to go well, the XXM plans will certainly produce some exciting, close-up images.

Posted by: sci44 Apr 13 2009, 06:45 PM

[temporarily deleted]


Posted by: ugordan Apr 13 2009, 08:27 PM

QUOTE (sci44 @ Apr 13 2009, 08:45 PM) *
There is a story on UT now:-

http://www.universetoday.com/2009/04/12/cassinis-indirect-image-of-boulders-and-moonlets-in-saturns-rings/

Hmm. I wonder how this "scoop" will go by some imaging team members...

Posted by: ustrax Apr 13 2009, 09:45 PM

QUOTE (ugordan @ Apr 13 2009, 09:27 PM) *
Hmm. I wonder how this "scoop" will go by some imaging team members...


Well...EDITED: Let's wait and see... rolleyes.gif

Posted by: ngunn Apr 13 2009, 10:03 PM

Don't miss Emily's great piece on this, with angles and heights. There must be quite a pile-up at the outer edge of that ring. Does it go all the way round?

I'm not normally a ring watcher, but this is the start of something not to be missed. It's eyes down for the magic shadow show.

Posted by: sci44 Apr 13 2009, 10:34 PM

Thats a fair point - I have nothing but respect for the work the Cassini imaging team, and they should get first stab at the data - I chopped my last post, but shall I just say I recommend N00133374.jpg as deserving close study (especially the left hand side of the region in question)..
smile.gif

Posted by: nprev Apr 14 2009, 12:46 AM

Just because I felt like linking to a random recent image of the rings, http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133374.jpg. Beautiful!!!!

Posted by: helvick Apr 14 2009, 12:56 AM

I just read Emily's excellent blog post and I have to say that she makes a good argument for the shadow causing features being a couple of km in height. I also have to say that my earlier comment where I said I thought it was unlikely that we should expect to see motion was off base - I was ignoring the frame of reference and target of the camera and I was not factoring in the nature of the disturbance that Mimas would be causing. I'm very keen to find out what the Cassini team has to say about these shadows in any case.

Posted by: Stu Apr 14 2009, 05:53 AM

Emily's piece on this is simply outstanding, a great piece of science journalism. It made this fascinating topic a LOT easier to understand for me. Thanks Emily!

( ... but then you go and ruin it by mentioning that ******* song at the end! It's 06.50 here in the UK right now, I'm just about to head out the door to go to work, and I know that tune will be going round and round in my head all freaking day now... !!! sad.gif tongue.gif )

Posted by: Astro0 Apr 14 2009, 02:10 PM

Just to put one final piece into this thread, here's a rough stitch of the images across the rings.
I've left the moon shadow from each image for effect.
When everything is in context it certainly makes for a pretty picture.



Try rotating the image for a completely different feel on the shadows.

I'm starting to think that we were definitely 'seeing more' than is actually there.
But how fascinating is it to contemplate the day when Cassini does get a close enough view of the ring structure and with enough images together to 'actually see' the particles move. smile.gif

Astro0

Posted by: elakdawalla Apr 14 2009, 04:29 PM

That's cool, Astro0, thanks for that. Although the edge of the B ring is the most "mountainous" place in your pan, when I wander around it I see some other noisier-looking spots -- I wonder if those are places where there's some topography to the rings.

--Emily

(P.S. Thanks, Stu. Having all of y'all's commentaries to start from makes things easy.)

Posted by: fredk Apr 14 2009, 09:01 PM

These are ridiculously spectacular images. Sorry if someone has already mentioned this, but there appears to be a correlation between the length of the ring shadow and the brightness of clumps in this ring, which certainly makes sense.

We can also obtain information about the extent of structures perpendicular to the rings elsewhere, by the absence of visible shadows. Where we can't see ring shadows, any shadow present must have a length of order 1 pixel or less. Using the figures quoted above (7 km/pixel scale, 1.9 degree sun angle), that means any structures elsewhere must be less than roughly 200 metres in height. Of course this limit will improve as the sun angle decreases...

Posted by: belleraphon1 Apr 14 2009, 10:41 PM

When CASSINI launched I never expected THIS!

A leapin and hoppin on a moom shadow ......... (thanks for that Emily... have not listened to the Cat in years)...
SO... just cannot stop the leapin and hoppin in my minds eye now.. a rainbow bridge of cascading light and shadows, along a bumpy grainy plain that sails off to the limits of our current vision.....

I am blown away.... how grand!!!!

Craig


Posted by: ngunn Apr 15 2009, 12:37 PM

APOD today. smile.gif The 'preliminary hypothesis' link goes to Emily's blog, and 'jagged shadows' comes straight here.

EDIT: Oh no . . . the 'cast' link goes to Cat Stevens . . .

Posted by: ngunn Apr 15 2009, 01:33 PM

Here's another calculation. I wanted to know roughly how fast the relative motions are between these jostling clumps.

Taking the peak amplitude of the displacement from the ring plane as 2 km and the radius and orbital velocity of the outer B ring as 117600 km and 17970 m/s respectively I get:

Maximum perpendicular velocity (whilst crossing the ring plane) = 2 x 17970 / 117600 = 0.3 m/s.

So, even for particles or clumps rising and falling exactly in antiphase, collision velocities would be less than 1 m/s.

Makes you realise just how gentle most of the rest of the rings must be.

Posted by: Stu Apr 15 2009, 01:50 PM

A few years ago the BBC produced a series called "Space Odyssey" (re-christened "Voyage To The Planets" for overseas markets) and while it wasn't 10000% accurate scientifically, it did feature some truly breathtaking images and visuals, such as an astronaut flying through Saturn's rings...

http://www.youtube.com/watch?v=tTrh26hBUlQ

The Saturn's rings EVA begins at 4.53 if you want to skip to that part.

The series got quite a lot of stick for being cheesy and melodramatic, but I've watched it again and again, just because it inspires such wonder when I do. Well worth checking out the DVD, or trawling YouTube for the rest of it.

Posted by: ngunn Apr 15 2009, 02:08 PM

Hey, that is indeed a beautiful animation of the ring particles, thanks Stu. (Best watched with the sound off though.)

Posted by: Fran Ontanaya Apr 15 2009, 02:09 PM

The great wall of Saturn... blink.gif

At the right side of the third frame there's a round spot, as if a free moonlet was casting a shadow on the wall of dust. To the left of it, a pillar of dust and its shadow seems to appear.



Posted by: volcanopele Apr 15 2009, 05:54 PM

QUOTE (ngunn @ Apr 15 2009, 05:37 AM) *
APOD today. smile.gif

Uh oh....

Posted by: chemman Apr 15 2009, 05:59 PM

QUOTE (Fran Ontanaya @ Apr 15 2009, 10:09 AM) *
The great wall of Saturn... blink.gif

At the right side of the third frame there's a round spot, as if a free moonlet was casting a shadow on the wall of dust. To the left of it, a pillar of dust and its shadow seems to appear.




Just noticed that myself and was going to post, but I see you beat me to it. Good observation. I think the background shadow you are attributing to the "pillar" might actually be the shadow of the moonlet instead. The shadows should appear at an angle to the corresponding foreground objects since this section of the ring is not directly parallel to the sun. Just my thoughts.

Posted by: ugordan Apr 15 2009, 06:10 PM

QUOTE (chemman @ Apr 15 2009, 07:59 PM) *
Just noticed that myself and was going to post, but I see you beat me to it.

I don't see it. All I see is the resize filter smoothing out unresolvable pixel values. A dark pixel inside a brighter area will tend to look circular, especially with the bicubic resample filter.

Posted by: chemman Apr 15 2009, 06:57 PM

QUOTE (ugordan @ Apr 15 2009, 02:10 PM) *
I don't see it. All I see is the resize filter smoothing out unresolvable pixel values. A dark pixel inside a brighter area will tend to look circular, especially with the bicubic resample filter.


I haven't done my own processing yet, but it appears it might be in the other images and moving. I don't know the time separation between the images so it's difficult to tell if the apparent object is moving at a constant rate. What caught my initial attention was the appearance of what appears to be a corresponding shadow in the last frame at an angle consistent with the shadows of the other ring objects. I agree though, with the resolution we have it could just be an illusion or a artifact of the image processing.

OK, after further review I concur it's a processing artifact. smile.gif

Posted by: jasedm Apr 15 2009, 07:10 PM

QUOTE (ugordan @ Apr 15 2009, 07:10 PM) *
All I see is the resize filter smoothing out unresolvable pixel values.


I was going to say that.. smile.gif

Posted by: Floyd Apr 16 2009, 12:02 AM

I started this thread because I was really blown away by the images of the outer edge of the B ring. I correctly guessed that many UMSFers would be fascinated as well. However, I didn't (and don't) believe finding the images scooped the Cassini team in any way. They had predicted that protuberances in the rings would cast informative shadows. See the following Cyclops news release of March 23, 2009.http://ciclops.org/view/5558/MOON_SHADOWS_SIGNAL_THE_APPROACH_OF_EQUINOX_AT_SATURN

Excerpts from the Cyclops news release:
[During equinox, Saturn's moons can shadow the rings], especially those whose orbits are inclined with respect to the equator, begin to intersect the planet's rings. When this occurs, the equinox period has essentially begun, and any vertical protuberances within the rings, including small embedded moons and narrow vertical warps in the rings, will also cast shadows on the rings. At exactly the moment of equinox, the shadows of the rings on the planet will be confined to a thin line around Saturn's equator and the rings themselves will go dark, being illuminated only on their edge. The next equinox on Saturn, when the sun will pass from south to north, is Aug. 11, 2009. … Because of these unique illumination circumstances, Cassini imaging scientists have been eager to observe the planet and its rings around the time of equinox, and Cassini's first extended mission, which began on July 1, 2008, and extends to Sept. 30, 2010, was intended to gather observations during this time. Hence, its name: Cassini Equinox Misson. … Cassini imaging scientists first predicted when and where the moons' shadows would fall on the rings and then planned special imaging sequences to target those locations. … More than just pretty pictures, these observations and others to come could provide valuable information regarding the presence of any deviations across the rings from a perfectly flat wafer-like disk. Working outward from the planet, the main rings are named C, B, and A. Saturn's ring system is wide, spanning hundreds of thousands of miles or kilometers. But the main rings are perhaps only 10 meters (30 feet) thick, and they lie inside the F ring which is vertically thicker than the A, B and C rings, making the determination of interior vertical deviations difficult when imaging the rings edge-on.

Assuming Bjorn Jonsson's calculations are correct (post 17), the outer edge of the B ring is warped approximately 3 km which is large compared to 10 meter ring thickness mention above. We at UMSF are certainly having a lively discussion and doing great things with the images, but I am quite sure that the Cassini team recognized the significance of these images as soon as they hit the ground. It may take the scientists a while to comment, but I'm sure they are all over this and planning additional sequences to get just the right images for publication.


Posted by: Astro0 Apr 16 2009, 01:49 AM

Perfectly said Floyd.

For the majority of contributors, UMSF'ers are armchair explorers only and for us it's just fun to ponder the possibilities and guess at what we are seeing. The Cassini team like all the other mission scientists and engineers are the experts, and they tell us the facts when they know them. We respect and appreciate the fact that they even share this data with the public at all. For the moment, we are just the wide-eyed audience on the outside looking at the magic they produce.

Posted by: ngunn Apr 16 2009, 09:01 AM

More vertical relief here?
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133497.jpg

Posted by: ugordan Apr 16 2009, 09:10 AM

Looks like it, nice catch. I wonder if Daphnis' slight inclination is forcing these waves to also have vertical excursions or if it's merely piling up of material somehow forcing it to spread vertically.

Posted by: Bjorn Jonsson Apr 16 2009, 09:41 AM

QUOTE (Floyd @ Apr 16 2009, 12:02 AM) *
I started this thread because I was really blown away by the images of the outer edge of the B ring. I correctly guessed that many UMSFers would be fascinated as well. However, I didn't (and don't) believe finding the images scooped the Cassini team in any way. They had predicted that protuberances in the rings would cast informative shadows. See the following Cyclops news release of March 23, 2009.http://ciclops.org/view/5558/MOON_SHADOWS_SIGNAL_THE_APPROACH_OF_EQUINOX_AT_SATURN

I'm not even sure these are the first images showing these shadows. I haven't checked every raw JPG image (far from it) - others here who have done so may know better. The shadows shouldn't just magically appear once the solar elevation angle drops below 2 degrees, they should be visible at higher angles as well - I wouldn't be surprised if they first appeared several months ago.

Posted by: ugordan Apr 16 2009, 10:22 AM

There probably were hints of the shadows for some time now, but it comes down to the observations executed, distance, etc. Also, these shadows could be a fairly localized phenomenon for all we know, not extending around the entire ring circumference.

In a way, spotting them is similar to Enceladus' geysers - they've been there all along but it took a combination of factors to make them noticeable.

Posted by: ngunn Apr 16 2009, 02:57 PM

Trawling through recent Daphnis images it looks like some shadows of disturbances were already visible on this image from January 31st:
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS47/N00128822.jpg

I don't suppose that's the earliest example either.

Posted by: Floyd Apr 16 2009, 03:37 PM

If Daphnis had 0 inclination, I wouldn't think it would pull ring material out of the plane. I would guess that it has a very slight inclination. If my math is correct, an inclination of .0042 degrees would place its center 10 km above (and below) the ring plane [sin(10/136,505) when maximally out of plane. Its diameter is listed in Wikipedia as 6-8 km. So at zero inclination it should stick up 3-4 km and throw an appropriate length shadow. If the shadow is longer than expected, then we can figure how much it can move above the ring plane and its inclination. I'll leave the trig analysis of pixels to someone with a better brain and more time than I.

Posted by: chemman Apr 16 2009, 04:57 PM

QUOTE (Floyd @ Apr 16 2009, 10:37 AM) *
If Daphnis had 0 inclination, I wouldn't think it would pull ring material out of the plane. I would guess that it has a very slight inclination. If my math is correct, an inclination of .0042 degrees would place its center 10 km above (and below) the ring plane [sin(10/136,505) when maximally out of plane. Its diameter is listed in Wikipedia as 6-8 km. So at zero inclination it should stick up 3-4 km and throw an appropriate length shadow. If the shadow is longer than expected, then we can figure how much it can move above the ring plane and its inclination. I'll leave the trig analysis of pixels to someone with a better brain and more time than I.


What we are seeing is the gravitation wake of Daphnis in the Keeler gap. The wake has both an radial and angular (vertical) components.

Reference this link for some cool simulations of the wake http://www.cs.trinity.edu/~mlewis/Rings/KeelerGap2005/

and this for a more mathematical treatment http://oldenhuis.info/Reports%20and%20Articles/Daphnis/daphnis.PDF

Cheers

Posted by: elakdawalla Apr 16 2009, 06:17 PM

Nice catch on the Daphnis wake shadows. I like the eensy little shadow that Daphnis itself makes on the rings as well. Seems like it should be possible to learn more about the size and even shape of Daphnis from looking at its shadow, but you'd have to know Daphnis' vertical position (if it deviates at all from being within the ring plane) and whether the ring itself had any warp at all to it.

I'm guessing it's not a coincidence that those shadows in the images we were originally discussing were located so close to Mimas' orbital position.

--Emily

Posted by: Floyd Apr 20 2009, 02:01 PM

The http://ciclops.org/view/5594/Rev109 (posted previously by ngunn) indicates that many images of interest are being taken. Nothing has appeared at raw image page since April 14th, guess the image pipeline from Saturn is no better than from Mars at he moment. tongue.gif

April 17-Shadows of Mimas and Tethys on A & B rings
April 24-Daphnis
April 29-Shadow of Tethys on A & B rings
April 30/May 1-Daphnis & shadow of Mimas on A & B rings

Posted by: ElkGroveDan Apr 20 2009, 03:47 PM

QUOTE (Floyd @ Apr 20 2009, 06:01 AM) *
guess the image pipeline from Saturn is no better than from Mars at he moment. tongue.gif


I didn't want to say anything, but when I was out at Goldstone last month with Doug I tripped over a cable. It gave off a few sparks and I smelled a bit of smoke. I was afraid something like this would happen.

Posted by: Floyd Apr 20 2009, 05:41 PM

Figured it must have been something that someone from UMSF did that wiped out the image pipelines. rolleyes.gif
And an Admin person to boot.

Posted by: Floyd Apr 21 2009, 04:07 PM

QUOTE (chemman @ Apr 16 2009, 11:57 AM) *
What we are seeing is the gravitation wake of Daphnis in the Keeler gap. The wake has both an radial and angular (vertical) components.
Reference this link for some cool simulations of the wake http://www.cs.trinity.edu/~mlewis/Rings/KeelerGap2005/
and this for a more mathematical treatment http://oldenhuis.info/Reports%20and%20Articles/Daphnis/daphnis.PDF


chemman
The simulation of Daphnis' wake is totally awesome. I also enjoyed the manuscript, but the math is a bit beyond me. Thanks for posting these great links. Welcome to UMSF if someone hasn't welcomed you previously.

Posted by: Floyd Apr 24 2009, 03:19 PM

This picture, http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133715.jpg, was taken April 16 in the F-ring series. Is there a groove at the top of Prometheus, or is this a shadow of the F-ring on Prometheus?

 

Posted by: dilo Apr 24 2009, 09:19 PM

QUOTE (Floyd @ Apr 24 2009, 04:19 PM) *
This picture, http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133715.jpg, was taken April 16 in the F-ring series. Is there a groove at the top of Prometheus, or is this a shadow of the F-ring on Prometheus?

Floyd, considering illumination from below, I tend to think is F-ring shadow.
Very interesting also the sequence of http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133736.jpg two ringlets, with clear shadow projeced above.
Below, I made elaboration of both images, with subtracted "dark field" (horizontal weak bands) and improved contrast/sharpening.

Posted by: Bjorn Jonsson May 2 2009, 02:16 AM

The recent images showing satellite shadows are interesting, e.g. this one:

http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=190253

The "brightness reversal" within the shadow near the bottom is interesting. This is the unlit side of the rings.

A wide angle frame taken a bit earlier:

http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=190230

Posted by: john_s May 2 2009, 03:34 PM

Very interesting! I'm guessing the brightness reversal occurs because in this particular geometry, that part of the rings is illuminated more by Saturn than by the Sun (e.g., maybe the image has a forward-scattering geometry for Saturn light, and that part of the ring is particularly forward-scattering. Or maybe it's an opaque part of the ring and not much sunlight gets through from the lit side). So it's still lit by Saturn even in the shadow.

Looking forward to all sorts of even cooler effects as the equinox approaches...

John.

Posted by: nprev May 2 2009, 06:48 PM

I notice that the edges of the umbral shadow become increasingly diffuse as they approach the apex of the cone. I swear that I also see the straight edge of the prenumbra as well, esp. on the left-hand side. Is this telling us something useful about the distribution of fine particles in this section of the rings, esp. that of any slightly above the ring plane?

It would be extremely interesting to catch a shadow across a spoke.

Posted by: Stu May 3 2009, 11:32 AM

Wow...

http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=190390

Discuss! smile.gif

Posted by: Bjorn Jonsson May 3 2009, 12:30 PM

An even more pronounced brightness reversal than in the earlier image I noticed. We are looking at the unlit (northern) side of the rings and what John pointed out must be happening here: Saturnshine illumination and the brightness is providing a measure of optical depth. Where the brightness is not reduced within the shadow the rings must be completely opaque and illuminated by Saturnshine only. In the dark areas within the shadow the rings are tenuous and therefore do not reflect a lot of Saturnshine. However, sunlight filters through them from the lit side.

Posted by: helvick May 3 2009, 01:11 PM

The explanation makes sense but what I can't get my head around is why the various opaque\not opaque ring bands then seem to be so similar in overall brightness outside of the shadow regions.

If it wasn't for the fact that the orbital mechanics make it impossible my first reaction would be that what we're seeing (especially in this image) is a shadow falling on a much lower ring region with the unshaded rings inhabiting an orbit that is substantially higher and thereby were outside of the shadow cone.

Posted by: scalbers May 3 2009, 03:20 PM

Yes this is a really neat image, as mentioned the shadow is sorting out the sunshine vs saturnshine components of the ring illumination. Really gives us a chance to understand what we're seeing in general with all the unusual ring illumination geometries. For me personally it gives a fuller appreciation of looking during past equinoxes to view the dark side of the rings through telescopes.

Posted by: Floyd May 3 2009, 06:55 PM

And I had thought that only the lit side of the rings had cool images. Here is a chronology of past encounters with links to some of the images and dates for future encounters. Dates are from Looking Ahead and Tour Dates 2009.

April 03 Titan encounter/Ring plane crossing north to south to sun-lit side
April 07
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133345.jpg
April 08 Closest Saturn
April 08
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133374.jpg
April 10
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133436.jpg
April 11 Ring plane crossing south to north to unlit side
April 16 Furthest Saturn---------------------------------------
Start Rev 109
April 17
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133705.jpg
April 19 Titan encounter/Ring plane crossing north to south to sun-lit side
April 23 Closest Saturn
April 24
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135131.jpg
April 26 Ring plane crossing south to north to unlit side
April 29
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135097.jpgApril 29 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135089.jpgApril 30 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135179.jpg & http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135167.jpgMay 02 Furtherst Saturn---------------------------------------Start Rev 110
May 02 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135213.jpg
& http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135211.jpg
May 05 Titan encounter/ Ring plane crossing north to south to sun-lit side
May 09 Closest Saturn
May 09 Mimas & Pandora shadows
May 09 Daphnis & Pan
May 10 Daphnis
May 11 Ring plane crossing south to north to unlit side
May 12 Mimas & Teths shadows
May 14 Pan
May 17 Furthest Saturn----------------------------------------
Start Rev 111
May 21 Titan encounter/Ring plane crossing north to south to sun-lit side


Posted by: Bill Harris May 3 2009, 09:29 PM

And, of course, we now see a http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135089.jpg on the rings:

Interestinger and interestinger...

--Bill

Posted by: stevesliva May 3 2009, 09:38 PM

QUOTE (Bill Harris @ May 3 2009, 05:29 PM) *
And, of course, we now see a http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135089.jpg on the rings

The little moon in the outer gap in that photo still casts no shadow, though.

Posted by: nprev May 3 2009, 10:37 PM

Not sure that's a moon, Steve; looks like a CR hit to me.

Posted by: Floyd May 4 2009, 12:06 AM

Definitely a CR hit. Daphnis would have a wake around it, as do all the Daphnis images linked in the table. I've tried to pick out one of the best images for each moon shadow set. I'll add more links as images come in. Images of Pan and Daphnis can be found using the Cassini Search Raw Images with Camera: Narrow Angle, Target: Pan or Daphnis and Observation Time, Newest. To get the images of Mimas, Tethys or other moon's shadows, you can't search on the moon as it is not in the image. Instead use Camera: Narrow Angle, Target: Saturn-RINGS, and Observation Time: approximately day before to day after. You can use Newest, except you get a lot of images as Cassini has taken ring movies which show up as a few pages of images.

Posted by: ngunn May 4 2009, 11:04 AM

QUOTE (helvick @ May 3 2009, 02:11 PM) *
what I can't get my head around is why the various opaque\not opaque ring bands then seem to be so similar in overall brightness outside of the shadow regions.


That very interesting observation prompted me to do some back of the envelope calculations. I obtained the following approximate results:

1. Surface brightness of the sunlit side of Saturn relative to the Sun = 1.2 x 10*-7.
2. Solid angle subtended at a typical ring particle by one hemisphere of Saturn relative to Sun = 5 x 10*5.
3. Present average cosine of illumination angle of saturnshine relative to sunshine crudely estimated to be 10.

1 x 2 x 3 = 0.6 or saturnshine 60% of sunshine.

These ring images remind me strongly of Bunsen's experiment to measure the luminosity of the sun which I have only last week repeated with my students.

(In this experiment a drop of oil is placed at the centre of a white filter paper, rendering that part of the paper more transparent. The filter paper is placed so that direct sunlight falls on one side, and light from a lamp on the other. The lamp is moved close in to the paper until the wet part appears the same brightness as the rest, from whichever side the paper is viewed. This occurs when the illumination is equal on both sides.)

Posted by: dilo May 5 2009, 05:15 AM

Very interesting observations, ngunn!
Correct me if I'm wrong, the reason of equal luminosity observed by helvick is that, in such ring portions, scattered light from the sun has the same intensity of reflected light from Saturn... ph34r.gif
(I didn't know the Bunsen experiment, looks pretty cool!)

Posted by: helvick May 5 2009, 06:33 PM

That's a brilliant explanation ngunn - and I love the bunsen experiment comparison. I know there are plenty of other examples of shadowed lighting revealing details\characteristics that are otherwise hidden but I really love this one.

Posted by: Floyd May 10 2009, 04:27 PM

May 9th images down. I'll post some links when I get back from Star Trek rolleyes.gif
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00135950.jpg
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00135952.jpg
Mimas http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00135954.jpg

Star Trek was great!! No shadows of the Enterprise on the rings, but flying out of Titan's atmosphere was cool.

Posted by: nprev May 10 2009, 08:01 PM

Ooooo!!!! Ahhhhh!!!! Seriously! blink.gif

That Daphnis shot is particularly wild; some of the wake knots look like they're casting little shadows of their own, while the moon isn't!

Which moon is casting that shadow on your last pic, Floyd? Mimas? I don't see any of the ring rocks anywhere nearby.

Posted by: Floyd May 10 2009, 08:16 PM

nprev, I think its Mimas. Updated my previous post.

Posted by: Stu May 12 2009, 11:21 PM

Quick animation of 6 of today's raws, showing the shadow of one of the moons (dunno which one) sweeping across the rings...

http://cumbriansky.files.wordpress.com/2009/05/animation1.gif

Posted by: Hynee May 14 2009, 12:21 PM

Propeller:

http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136051.jpg
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136052.jpg



 

Posted by: john_s May 14 2009, 05:28 PM

Good eye! I would never have noticed that. It's looking like most of the disturbances in the ring are 3-D, not just 2-D.

John

Posted by: Floyd May 16 2009, 03:16 PM

April 03 Titan encounter/Ring plane crossing north to south to sun-lit side
April 07
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133345.jpg
April 08 Closest Saturn
April 08
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133374.jpg
April 10
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133436.jpg
April 11 Ring plane crossing south to north to unlit side
April 16 Furthest Saturn--------------------------------------------------------------------------------------------------
Start Rev 109
April 17 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133695.jpg
April 19 Titan encounter/Ring plane crossing north to south to sun-lit side
April 23 Closest Saturn
April 24
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135131.jpg
April 26 Ring plane crossing south to north to unlit side
April 29
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135097.jpgApril 29 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135089.jpgApril 30 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135179.jpg & http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135167.jpgMay 02 Furtherst Saturn--------------------------------------------------------------------------------------------------Start Rev 110
May 02 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135213.jpg
& http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00135211.jpg
May 05 Titan encounter/ Ring plane crossing north to south to sun-lit side
May 09 Closest Saturn
May 09 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00135955.jpg & Pandora shadows
May 09 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00135952.jpg & http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00135950.jpg
May 10 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136167.jpg, http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136164.jpg, http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136141.jpg& http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136084.jpg-
May 11 Ring plane crossing south to north to unlit side
May 12 Mimas & Teths shadows (I didn't find them?)
May 14 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136255.jpg
May 17 Furthest Saturn---------------------------------------------------------------------------------------------------
Start Rev 111
May 21 Titan encounter/Ring plane crossing north to south to sun-lit side
May 24 http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136349.jpg& http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136361.jpg
May 25 Closest to Saturn/periapse
May 25 A-Ring images of Encke and Keeler gaps-looking for topology
May 26 Ring plane crossing south to north to unlit side
May 27 Moon shadows Pan & Mimas
May 27 Daphnis in Saturn's shadow
May 30 Moon shadows Mimas, Pan & Prometheus
June 01 Moon shadows Pandora, Pan & Mimas
June 02 Furthest from Saturn/apoapse---------------------------------------------------------------------------------
Start Rev 112
This is an update with several more links plus Rev 111 image plan

Posted by: Floyd May 25 2009, 02:46 PM

Great image of Daphnis shadows. http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136361.jpg Thirty images of Pan and shadow. http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136349.jpg
Someone more skilled than I could make a great movie. [The Cassini links and images seem to come and go.]


 

Posted by: scalbers May 25 2009, 04:01 PM

Here even with my eyes it's remarkable how the 3-D aspects of the perturbations are there for us to see.

Posted by: alan May 25 2009, 05:43 PM

I wonder if Daphnis bobs up and down relative to the ring plane. It would be interesting to watch its shadow on the rings to see if the length oscillates.

Posted by: Floyd May 25 2009, 08:52 PM

Daphnis' orbit might be ever so slightly inclined relative to the rings. If one could image it in its orbit from 45 degrees before closest approach to sun to 45 degrees past, Daphnis could (if you are lucky in how the axis of inclination lined up with the direction of the sun) move from maximally above or below ring plane to zero, of zero to maximally above or below. I don't think there is any mechanism that would allow it to bob up and down quicker than one orbit, which just equals an inclined orbit.


Posted by: ngunn May 25 2009, 08:59 PM

QUOTE (Floyd @ May 25 2009, 09:52 PM) *
I don't think there is any mechanism that would allow it to bob up and down quicker than one orbit, which just equals an inclined orbit.


Not sure about that - what about the gravitational field of the rings themselves? The disturbed wake material looks as if it's bobbing up and down.

Posted by: Fran Ontanaya May 25 2009, 10:49 PM

Or Daphnis gravity field isn't spherical nor aligned with the rings. Depending on which side of the moon the particles approach to, they would end above or under the plane.

Posted by: Floyd May 25 2009, 10:58 PM

I agree that the ring material is bobbing up and down. Don't know about Daphnis. It would be important to know the mass of Daphnis vs the mass of the particle bunches we see bobbing.

Posted by: Gsnorgathon May 26 2009, 01:26 AM

How sure are we that the perturbation is purely gravitational? Could the ring particles be colliding as a result of Daphnis's passage?

Posted by: ngunn May 26 2009, 06:54 AM

QUOTE (Floyd @ May 25 2009, 11:58 PM) *
It would be important to know the mass of Daphnis vs the mass of the particle bunches we see bobbing.


Why would that be critical in this context? Ring particles and Daphnis alike are in free fall. Shouldn't they respond the same way to whatever field is present?

Yes there must be either collisions or viscous drag of some kind to damp out the bobbing in the case of the ring particles, but not Daphnis in its gap.

Posted by: ngunn May 26 2009, 07:30 AM

Straightforward application of Kepler's third law would tell us how fast that ring edge is drifting past Daphnis. That combined with the observed wavelength of the wake perturbations should yield the number of bobs per orbit (or orbits per bob?). Anybody fancy the maths? I can't - I've got a busy day.

Posted by: Floyd May 26 2009, 12:29 PM

QUOTE (chemman @ Apr 16 2009, 11:57 AM) *
What we are seeing is the gravitation wake of Daphnis in the Keeler gap. The wake has both an radial and angular (vertical) components.
Reference this link for some cool simulations of the wake http://www.cs.trinity.edu/~mlewis/Rings/KeelerGap2005/
and this for a more mathematical treatment http://oldenhuis.info/Reports%20and%20Articles/Daphnis/daphnis.PDF
Cheers


Ngunn & Gsnorgathon, I think the above simulation and paper are very relevant to this discussion. Ngunn, I mentioned mass, because that of Daphnis is big enough to kick up a wake that bounces ring particles both radially and angularly (up and down) without the particles having enough mass/gravity to perturb/bounce Daphnis. It would sure be nice if one of the authors of the PDF could comment--or anyone else who is an expert in orbital mechanics--which I'm not.

Posted by: scalbers May 26 2009, 01:32 PM

There is the very simple consideration that when two objects are perturbing each other, the more massive one will move less and the less massive one will move more. It makes sense to me that the rings could try to pull Daphnis bobbing up and down if they are massive enough. Perhaps a relatively simple model could show this?

As an analogy I believe that we (with the Sun) bob up and down in the plane of the Milky Way galaxy.

Posted by: ngunn May 26 2009, 01:57 PM

Yes. The rings must have an effect on Daphnis, though, by adding a restoring force toward the ring plane. If the resonant period of the resulting vertical motion is close to the orbital period (or a multiple or a sub-multiple) this might even maintain the non-zero eccentricity and inclination of Daphnis which otherwise you might expect to get damped out eventually. The particles at the gap edges would, I now realise, experience a bigger restoring force than Daphnis itself because the very nearest part of the rings would contribute a significant fraction of the total and for Daphnis that nearest part is missing (most of the time - I think its eccentricity takes it quite close sometimes).

I realise that the reality of all this is much too complex for my kind of handwaving analysis, but I enjoy trying to build my own first order approximate understanding of what is going on whenever possible. Thanks for the links. See also this, from Ciclops:
http://ciclops.org/view_media/5598/Discovery_of_the_Wavemaker

Posted by: ngunn May 26 2009, 06:23 PM

This sounds like one to read - pity I don't have access to it.
http://www.iop.org/EJ/article/0004-637X/680/2/1569/73975.web.pdf

Aha! Here it is in poster format:
http://gemelli.spacescience.org/~hahnjm/conferences/DPS/2007/poster.pdf

Posted by: Gsnorgathon May 26 2009, 08:07 PM

Floyd - thanks for the link to the simulation. I'm mortified to admit I'd previously seen those, but just watched the vids in "ooh-aah" mode. That oughta teach me.

Posted by: Floyd May 26 2009, 08:48 PM

ngunn: nice abstract. Do I understand correctly that in the long term for Pan and Daphnis, e and i are damped to 0 and therefore they have stable orbits. The ripples we see (with shadows) are a more short term effect than described in the abstract?
scalbers: you are of course correct that there are always reciprocal effects. Big mass little effect--Little mass big effect.
ngunn: Daphnis may therefore bob a little relative to its mass vs ring particles. However, the induced motion of the ring edges seems to be both up and down--as well as in and out radially. Could it be that the complex sinusoidal shape created has a net zero vertical and radial gravitational effect on Daphnis?

Posted by: ngunn May 26 2009, 09:29 PM

I hesitate to comment further, given the complexity of the situation, the sophistication of the published analysis and my almost total ignorance, but here's how it seems to me reading the Hahn poster.

There are Daphnis-ring interactions working both ways. Some mechanisms pump up the inclination and eccentricity while others damp them. The ultimate cut-off for the eccentricity seems to be the point at which the moon collides with the ring edge. At this point damping is enormously increased, presumably for both e and i. So we could be looking at a system which varies in an irregular way, mostly within narrow limits but with a safety barrier in place to chop off any sudden spikes in the orbital parameters.

One theme runs through this: there are undoubtedly dissipative processes involved, so there must also be an energy source. I haven't a clue what form that takes. Gradual widening of the gap? It's slow migration, along with Daphnis, either inward or outward? Angular momentum somehow transferred from one of the larger moons via resonance? I stand in awe of this whole mid-boggling circus and of the efforts of those who have the daunting task of sorting out its workings. I wish them luck! For me, it's back to the sofa with a glass of home brew. smile.gif

Clarification relating to your last question: I never meant to suggest that the vertical waves in the wake have a significant reciprocal effect on Daphnis, only that the rings as a whole acting as a planar mass must have - a very simplistic point.

Posted by: Floyd May 27 2009, 12:14 AM

A whole new series of images of Daphnis taken on May 25th. N00136503-N00136509 plus a few more where only ripples are visable.
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136503.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136504.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136505.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136506.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136507jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136508.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136509.jpg


Posted by: Floyd May 27 2009, 01:03 AM

Also a new propeller N00136512-N00136519. It comes in from the left just outside (below) the Encke gap in image 12 and goes out the right side of image 19.
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136512.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136513.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136514.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136515.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136516.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136517.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136518.jpg;http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136519.jpg

Posted by: ilbasso May 28 2009, 01:29 AM

"Propeller" is not a term I'm familiar with in this context. I see the phenomenon you're referring to, but what's the significance of calling it a "propeller"?

Posted by: alan May 28 2009, 01:42 AM

http://www.nasa.gov/mission_pages/cassini/multimedia/pia07792.html

Posted by: ilbasso May 28 2009, 02:13 AM

Thank you. I had missed that Cassini release in March.

Posted by: bkellysky May 29 2009, 10:08 PM

The "ubergeeks" at unmannedspaceflight.com are saluted in David Grinspoon's Cosmic Relief column in July's Sky and Telescope, which arrived in my mailbox today !

Posted by: dilo Jun 1 2009, 01:32 PM

QUOTE (Floyd @ May 27 2009, 01:14 AM) *
A whole new series of images of Daphnis taken on May 25th. N00136503-N00136509 plus a few more where only ripples are visable.

Herebelow a gif animation of the 6 frames (only rotation+center crop, no tilt correction):


 

Posted by: hendric Jun 1 2009, 02:38 PM

Will we have enough time to watch the next wave pop up before edge-on is over?

Posted by: nprev Jun 1 2009, 05:20 PM

Question: Could these be considered standing waves, or maybe even solitons? They look pretty stable in that sequence.

Also, I suspect that their structure is more complicated than they look here. Been visualizing something like a polarized radar pulse with a third dimension & a helical component.

Posted by: Adonis Jun 2 2009, 11:18 PM

I'd like to perform some basic calculations of aproximate elevations of some moonlets and waves above the ring plane. The problem is that the position of Cassini spacecraft relative to Saturn & Sun is needed, and that requires the hour of the day the individual Cassini images were shot. Info released along with Cassini images only comprise the day, but not the hour within the day. ¿is there any way to know the hour-of-the-day info of the moment a given image was shot by Cassini?

Posted by: Floyd Jun 5 2009, 11:22 PM

For really intelligent answers to a lot of questions raised on this thread, see the great entry on Emily's Planetary Society Blog by guest blogger http://www.planetary.org/blog/article/00001975/. Wow!


Posted by: rlorenz Jun 6 2009, 12:13 AM

QUOTE (Adonis @ Jun 2 2009, 07:18 PM) *
I'd like to perform some basic calculations of aproximate elevations of some moonlets and waves above the ring plane. The problem is that the position of Cassini spacecraft relative to Saturn & Sun is needed, and that requires the hour of the day the individual Cassini images were shot. Info released along with Cassini images only comprise the day, but not the hour within the day. ¿is there any way to know the hour-of-the-day info of the moment a given image was shot by Cassini?

All that information (image time to the second) is in the PDS headers, which you can get when the validated data is released for scientific work.

Posted by: scalbers Jun 6 2009, 03:17 PM

QUOTE (Adonis @ Jun 2 2009, 11:18 PM) *
I'd like to perform some basic calculations of aproximate elevations of some moonlets and waves above the ring plane. The problem is that the position of Cassini spacecraft relative to Saturn & Sun is needed, and that requires the hour of the day the individual Cassini images were shot. Info released along with Cassini images only comprise the day, but not the hour within the day. ¿is there any way to know the hour-of-the-day info of the moment a given image was shot by Cassini?


The raw images do give an approximate distance to the RINGS, so that information can in principle be combined with an ephemeris to yield the time. I've had some luck doing this with raw images of the satellites. Backing out the times of ring images might be trickier as it's unclear to me which part of the rings (or Saturn) is referenced in the distance.

Posted by: peter59 Jun 9 2009, 06:34 PM

Two months before the equinox game of light and shadow reveals more and more details. On these pictures clearly seen that the edge of the ring extends above the plane of the ring.
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00137394.jpg
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00137396.jpg

Posted by: jasedm Jun 10 2009, 01:12 PM

Interestinger and interestinger. I'm really looking forward to the equinox - the next four or five Titan encounters pump Cassini's ringplane inclination down to below 20 degrees in August/September, and periapse goes from 570,000km currently, to half that distance in August/September - literally a ringside seat!
Can't wait!

Posted by: Greg Hullender Jun 10 2009, 05:50 PM

Does anyone know at what point the rings will go dark and how long they'll stay dark? Or is that among the things we're expectingg to learn?

--Greg

Posted by: ugordan Jun 10 2009, 05:59 PM

They won't get completely dark because Saturn will still be illuminating them from both sides. They will get pretty dark, though, but probably only close to the actual plane crossing.

Posted by: Greg Hullender Jun 10 2009, 06:03 PM

Thanks. I went and read the suggested post on Emily's blog and figured that out too, but I was too late to edit my original. :-)

It does surprise me that the reflected light from Saturn has such a strong effect, though. I'd expect it to be just a few percent of solar illumination. (I'm too lazy to work it out right this second, but it's obvious that at some amount of tilt, the two are equal.)

--Greg

Posted by: ngunn Jun 10 2009, 08:48 PM

Greg, I'm sure you're after more accurate information, but I did give a rough calculation in post 72 of this thread which may be of some interest (in case you missed it). I assumed a solar elevation angle of between 1 and 2 degrees there.

Posted by: Greg Hullender Jun 11 2009, 05:43 AM

QUOTE (ngunn @ Jun 10 2009, 12:48 PM) *
. . . I did give a rough calculation in post 72 of this thread which may be of some interest (in case you missed it).

I did miss it, but it's quite interesting. I note that I match some of your numbers, coming at it from a different angle. I start by picking a point in the B ring (near the inner edge) where Saturn subtends exactly 60 degrees. That means it covers 6.7% of the sky. Since Saturn has a geometric albedo of 0.47, it'd be 47% as bright as the sun if it were a sheet covering half the sky. Hence our ring particle ought to get 6.3% as much light from Saturn (the whole planet) as it does from the Sun -- assuming nothing else is in the way. I think this is very close to the number you got for this part of the problem.

But the other parts of the ring do get in the way, and we can assume that the illumination from the Sun drops as the sine of the ring tilt. (Or cosine if we're talking angle of illumination, I guess.) But we should make the same assumption for the light from Saturn itself, right? Saturn's equator doesn't illuminate the rings at all, but as you go further north or south, the amount of illumination increases -- except, of course, the planet narrows too. I don't feel like setting that integral up tonight, but I'm guessing it'll drop the Saturnshine component by about a factor of 5. (And that's constant, of course; it doesn't depend on the ring tilt). At that point we can figure out the point where solar illumination drops below illumination by Saturn.

Again, I'm saying "ring tilt" to refer to the angle between the ring plane and a line connecting Saturn and the Sun.

Sound right so far?

--Greg

Posted by: Greg Hullender Jun 12 2009, 01:30 AM

Okay, I think I've worked it out. I think the only naive assumption is that Saturn's disk is equally bright, even though we know there ought to be at least some limb darkening.

So using the logic above, I come up with 1.6 degrees. That is, when the rings are within 1.6 degrees of the vector to the sun, the solar illumination and the "Saturnshine" should be equal. We'd have reached that point on April 28. Of course, my naive assumption overstates how bright the Saturnshine is.

This agrees fairly well with the estimate in post 72, particularly when you consider that I've chosen a point a good bit closer to Saturn.

Summary: I think it's fair to say that by now at least the inner rings are more brightly lit by Saturn than by direct sunlight. Of course, this effect diminishes as you go around the planet, so the view from above should already show the rings being a good bit brighter in front of Saturn, getting darker as they approach the shadow in the back, and with this effect more pronounced for the inner rings. Does anyone have a pic of that?

--Greg

Posted by: alan Jun 12 2009, 02:52 AM

this one shows that effect, although I not sure it is not showing the side not directly lit by the sun

http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=191742

edit : Ooo, triple negative, have fun parsing that

Posted by: volcanopele Jun 12 2009, 03:26 AM

Nope, good catch alan, that was the one I was looking for smile.gif

That image shows the "unlit" side of the rings, well, for now let's just call it the north side of the rings to avoid confusion..

Posted by: Greg Hullender Jun 12 2009, 04:47 AM

Although on the unlit side, we definitely expect to see the effect -- especially on the B Ring.

Now let me admit to a math error that totally changes the results. The numbers from before just seemed to be too large, and, yeah, they are. I got the double integral right (I think) but made a trig error, so I integrated the wrong thing. :-( (Never trust results you got by hand while waiting in the doctor's office . . .)

At the distance of the B-ring, Saturn is 3.14% as bright as the Sun. However, because Saturn's light falls obliquely on the rings, the maximum illumination is 48 times less than that, or about 0.13% what the Sun could do, if it shone directly on the rings. Even tilting the rings, as long as there are more than two minutes of arc, the Sun should still be brighter.

And I'm still overestimating how bright Saturn really is, I think, so, based on that, I'd predict that we won't be able to see the Saturnshine effect at all on the sunlit side of the rings (that's the south side, right now) except for a few hours on the day of the equinox itself.

This hypothesis is supported by the photo. It shows that the Saturnshine effect is weak even on the backlit, north side of the rings. You'd expect direct sunlight to wash it out, given that even backlighting is brighter.

--Greg

Posted by: chemman Jun 13 2009, 12:27 AM

Hello all!

I received a news release announcement from CICLOPS in my inbox yesterday and thought I would pass it along.

Saturn's Approach To Equinox Reveals Never-before-seen Vertical Structures In Planet's Rings

http://ciclops.org/view.php?id=5680

Great animation under "wave shadows in motion"

http://ciclops.org/index.php

The abstract for the article by John Weiss et al can found here.

http://www.iop.org/EJ/abstract/1538-3881/138/1/272

Looks like you can purchase the full article for $9US if anyone is interested

Enjoy

Posted by: chemman Jun 14 2009, 08:20 PM

Ok, I decided I was interested and obtained a copy of the article. All and all it’s a very well written article which examines the effects of moon orbital eccentricity and inclination on ring gap edges. The resulting wave amplitudes and morphology were examined for the moon-gap cases of Pan-Encke and Daphnis-Keeler.

(Note, I was writing a much more detail article summary, but something happened and my browser page tab disappeared along with every thing I had written. I couldn’t bring myself to rewrite everything (was almost done sad.gif ) so here’s a more condensed summary.

Some Daphnis-Keeler useful values:
Diameter- ~ 9 km
Keeler gap ~ 35 km
Moon-gap edge distances: 13-20 km (inner) and 14-16 (outer)

(Note: The inner edge of the Keeler Gap is in a 32:31 inner Lindblad resonance with Prometheus, causing the edge’s radial location to vary over a 15 km range and hence the larger range of Moon-gap edge distances)

Wave Amp (radial): 1.8 – 5.4 (inner) and 4.0-5.6 (outer)
Eccentricity – 3.31x10-5
Inclination – 0.0036 deg (vertical variation 8.6 km)
Orbital period – 0.594 days
Synodic orbital period – 8.5 years (5210 orbits)
(It’s interesting to note that due to angular momentum interactions with the ring, the longitude of Daphnis’ ascending node undergoes precession. This means that it will take 5210 orbits for Daphnis to reach the same relative position in space twice!)

For a circular-coplanar moon/ring orbital geometry the edge wave is primarily radial with constant wave morphology.

For an eccentric-coplanar moon/ring orbital geometry the edge wave is still primarily radial but wave amplitude now varies with time.

Orbital inclination imparts a vertical component so the wave will now display radial and vertical amplitudes. In the case of the Daphnis, the moons orbit is both eccentric and inclined relative to the ring. Because we now have 2 parameters effecting the moon ring orientation the overall wave morphology will display a large temporal variation. The orbital positions for radial and vertical wave amplitude maximum are ~ 180deg apart. Meaning when the vertical amplitude is at a maximum the radial amplitude will be at a minimum. According to the simulations performed by the authors the radial amplitudes will vary from 2.0 – 7.7 km and the vertical amplitude will vary from 0.2 – 1.7 km. Based on the shadow lengths from latest Cassini images of Daphnis (may 09) they calculated that the vertical amplitude was 1 – 1.5km and that the wave morphology was consistent with this height.

If you examine the images of Daphnis and the associated ring edge waves you will notice that the inner edge shows reduced amplitude compared to the outer edge. Apparently this is due to the eccentricity of Daphnis’ orbit which causes it to typically be closer to the outer ring edge and also in part to the fact that the inner edge particles experience a resonance effect from the moon Prometheus.

In relation to some of the discussion here regarding effect of the ring particles on Daphnis, they estimated that the mass of effected ring particles at any one time is ~ 0.0014 times the mass of Daphnis. As I noted previously, the ring particles do cause the ascending node of the orbital inclination to undergo precession. Additionally the ring particle also are causing a slight damping effect on the inclination (damping period ~ 1000 years). Apparently depending on the mass of the ring the orbital inclination can experience a damping or exciting effect and Daphnis is deemed to be right around the critical point for damping vs. excitation.

Let me know if anyone has questions or comments. Additionally I didn’t post the paper because I felt that would constitute too blatant of a violation of my single use license. However if anyone really would like to see the paper just send me a separate message and I can probably be convinced to allow you to borrow my copy wink.gif

Posted by: dilo Jun 15 2009, 08:56 AM

Thanks chemman for very interesting resume (is a shame not to have your initial richer report!).

QUOTE (chemman @ Jun 14 2009, 09:20 PM) *
In relation to some of the discussion here regarding effect of the ring particles on Daphnis, they estimated that the mass of effected ring particles at any one time is ~ 0.0014 times the mass of Daphnis.

This is stunning, they estimated the mass of astronomical "object" which is only 120 million tonns (comparable to the mass of a 500m wide iceberg...!). Perhaps a record (Itokawa, as example, is 3 times more massive), and for sure impressive considering also is referred to a "diffuse" assembly of tiny particles...
I guess they derived such a value from ascending node precession, do you confirm?

Posted by: chemman Jun 15 2009, 01:09 PM

QUOTE (dilo @ Jun 15 2009, 03:56 AM) *
Thanks chemman for very interesting resume (is a shame not to have your initial richer report!).


This is stunning, they estimated the mass of astronomical "object" which is only 120 million tonns (comparable to the mass of a 500m wide iceberg...!). Perhaps a record (Itokawa, as example, is 3 times more massive), and for sure impressive considering also is referred to a "diffuse" assembly of tiny particles...
I guess they derived such a value from ascending node precession, do you confirm?



Hello Marco - Yes I was quite upset when I lost my initial report, half way into it I actually though to myself that I should transfer it to a different program so I would not lose it, but never did. Oh well, If I get time again soon I may make another pass at a more in depth summary.

They estimated the mass of the effected ring particles by estimating the radial and longitudinal dimensions of the interacting patch of the ring (2.5km radial by 165km longitudinal) and using a surface density of 30g/cm (based on density wave measurements from another paper). They said this then gives a combined mass for the interacting ring edges of ~ 0.0014 times the mass of Daphnis. They pointed out that this is a order of magnitude estimate only and that a 10% difference in the estimate ring mass would cause their initial calculation of orbital inclination damping to become exciting. Then end up using another more accurate method to calculate a damping period of 1000 years for the orbital inclination.

Posted by: Floyd Jun 15 2009, 04:08 PM

chemman--Thanks for a really great summary. I've also lost a few posts (hit go back when I meant to tab between windows), but usually copy to Word as I never catch the misspelling of typos otherwise.

Do they comment on other factors (resonance with other moons) that could keep Daphnis slightly inclined? It seems unlikely that we just happen to be viewing it a mere 1000 years before its inclination gets damped out.


Posted by: chemman Jun 15 2009, 10:31 PM

QUOTE (Floyd @ Jun 15 2009, 12:08 PM) *
chemman--Thanks for a really great summary. I've also lost a few posts (hit go back when I meant to tab between windows), but usually copy to Word as I never catch the misspelling of typos otherwise.

Do they comment on other factors (resonance with other moons) that could keep Daphnis slightly inclined? It seems unlikely that we just happen to be viewing it a mere 1000 years before its inclination gets damped out.



They don't mention any else that might effect the inclination. I get the impression that since Daphnis-Keeler gap system seem to be right around the cutoff for orbital damping, it would not take much error in their calculations to get a different out come. Typically ring moon interactions for inclination should not be stable unless there is a counter acting force. That begin said, they did comment on the fact the Daphnis had a eccentric orbit which surprised them since they thought the eccentricity should have disappeared due to ring interactions. They didn't speculate on any reasons for the apparent stability of the eccentricity.

Posted by: ngunn Jun 29 2009, 06:37 PM

Shadows lengthening fast now:

http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS51/N00138316.jpg

http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS51/N00138317.jpg

Posted by: john_s Jul 6 2009, 07:22 PM

A dramatic illustration of how the illumination of the dark (north) side of the rings is now dominated by reflected Saturn-light http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=194656. Note how much brighter the rings are on the day side of the planet, where Saturn-shine is stronger. Note also the contrast reversal between the B and C rings around the ring- the C ring is brighter where transmitted sunlight dominates, the B ring is brighter where Saturn-shine dominates.

John


Posted by: jasedm Jul 6 2009, 08:51 PM

Equinox is only 5 weeks away now - I'm wondering what light (no pun intended) will be cast on the ring-spoke phenomena when the rings darken? Will they be much more evident against the dark backdrop, or be completely invisible?

Posted by: nprev Jul 6 2009, 11:41 PM

Would like to see some near-edge-on shots that might possibly capture spokes 'levitating' above or below the main ring plane; assuming that they'd scatter a bit more light at that point than the rings proper.

Posted by: jasedm Jul 9 2009, 09:20 AM

Agreed - this would be great!
Incidentally, further to my earlier post, doubtless it's no coincidence that we'll be right on top of the equinox. I understand that Cassini's Rev116 periapse is on the day itself (11th August), and occurs between the orbits of Janus and Mimas - the lowest for over a year. Kudos once again to those who control the orbital trajectory...

I'm hoping there might be some blog posts from the team during equinox, similar to those for the last couple of very close Enceladus flybys - I'd LOVE to see a simulation showing instrument pointing for the busiest part of periapse.
smile.gif



Posted by: Ian R Jul 15 2009, 06:24 PM

For a different perspective on the whole issue of moons casting shadows on the rings, here is a mosaic of a couple of HST pictures of Saturn (taken back in 1995, as far as I can recall):


Posted by: ngunn Jul 16 2009, 09:50 AM

Daphnis makes a real three-dimensional mess:

http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS51/N00138916.jpg

Posted by: john_s Aug 4 2009, 09:45 PM

New raws up: http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=196842 My guess- sunlight coming through the Cassini division from the sunlit side and illuminating 3-D irregularities on the dark side at the outer edge of the B-ring.

Second thoughts- I don't think that works, because there are shadows cast in one direction and streaks in another direction. Maybe this is the lit side after all. Hmmm....

John

Posted by: volcanopele Aug 4 2009, 10:13 PM

That's along the edge of the B ring yes, but this is the lit face of the rings

Posted by: ugordan Aug 4 2009, 11:23 PM

Let me just say whoa! blink.gif

Notice how the gap to the right is wider at the top than at the bottom. This disturbance almost looks like it's waves splashing onto a beach or in this case onto the gap. Could those fuzzy white things be vertical protrusions above the plane and merely look skewed due to viewing geometry?

Posted by: nprev Aug 5 2009, 12:01 AM

QUOTE (ugordan @ Aug 4 2009, 03:23 PM) *
Could those fuzzy white things be vertical protrusions above the plane and merely look skewed due to viewing geometry?


That's definitely my impression, Gordan. Utterly, hypnotically amazing!

Posted by: ugordan Aug 5 2009, 12:14 AM

Hmm, there's a tiny bit of overlap between frames 139391 and 392 and even though there's a very slight perspective change (whether primarily due to Cassini moving or rings rotating), there's no noticeable 3d effect which I'd expect if these were tall structures. In fact, if you rotate the image you can almost convince yourself these are flat features.

One thing's for sure, this disturbance looks confined to just a small segment of the ring circumference. The majority of other frames show slightly rough material, but more well-behaved.

Posted by: alan Aug 5 2009, 04:51 AM

reminds me of this image
http://pds-rings.seti.org/neptune/voyager/c1141246.html

I also notice that on the browse page the images showing the streaks are darker. Perhaps the shorter exposure plus smearing due to the orbital motion allowed the radial motion of some clumps in the rings to be captured. The streaks do appear to be in part of the ring where the distance to the edge of the ring and the narrow ring outside it is changing.

ETA: moonlet with shadow in this image?
http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=196899

Posted by: dilo Aug 5 2009, 10:42 AM

QUOTE (john_s @ Aug 4 2009, 10:45 PM) *
New raws up: http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=196842

This enhanced version can be useful:


With illumination change, the images are more and more amazing! look at this Prometheus picture projecting a sharp shadow on the rings:
http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=197449

Posted by: phase4 Aug 5 2009, 11:23 PM

Incredible.

In order to comprehend (with my tiny uneducated brain) what cosmic forces are at work here I downloaded the full image sequence.
It looks like the ring has been evolving up too close to the next and is refitting it's course. The white streaks might be debris from
numerous collisions as waves of moonlets are crashing into one and other. But that's just my amateur imaginative guess.

Hopefully a scientific explanation will come along. It's an absolutely amazing phenomena... I can't stop looking at it.

Posted by: stevesliva Aug 6 2009, 03:55 AM

I don't want to jinx anything, but... HOW PRICELESS ARE THESE IMAGES?!?!

Holy schmoly, we won't duplicate them for probably 45 years. At least.

Posted by: Hungry4info Aug 6 2009, 05:55 AM

I really don't understand that image of the rings.

I can see how some of the features and some shadows correspond, but yet others don't seem to.
I'm lost. blink.gif

Posted by: volcanopele Aug 6 2009, 06:10 AM

Just a note, some of the streaking and fuzziness in the image is the result of the longer exposure times ring scientists on the imaging team have had to use as the sun get lower and lower on the ring plane.

Posted by: Ian R Aug 6 2009, 07:21 AM

Here's a quick-'n'-dirty mosaic of two of the raw images:


Posted by: Hungry4info Aug 6 2009, 08:42 AM

QUOTE (volcanopele @ Aug 6 2009, 12:10 AM) *
Just a note, some of the streaking and fuzziness in the image is the result of the longer exposure times ring scientists on the imaging team have had to use as the sun get lower and lower on the ring plane.


Does that account for the appearance of some of those... ring bumps? They seem like they were eroded by wind toward the top-left of the image.
(yes I know, no wind in space laugh.gif )

Edit: Never mind. If so, it would modify the appearance of ALL the ring bumps.

Posted by: belleraphon1 Aug 6 2009, 01:12 PM


The complexity perplexes me.

Sitting here thinking how 30 years ago we were less than a month away from the Pioneer 11 Saturn encounter. With Voyager 1 to follow in 1980. These were the first spacecraft to flyby Saturn.... I do not think any of us, back then, could have imagined what was to come.

The rings are a gold mine of data for researchers ..... and just plain beautiful.

I am euphoric!

Craig


Posted by: Floyd Aug 6 2009, 06:05 PM

Wow, really amazing. VP, I don't think I see much streaking as there are a lot of un streaked spots (clumps/boulders). Could the diagonal ridges be due to some orbital resonance with one of the larger moons? For the F-ring, the gores point towards the moon. Is there some mechanism where the perpendicular to the ridges could be pointing towards the moon driving the ridge formation??


Posted by: phase4 Aug 7 2009, 09:08 AM

Here's a rough composition of 8 pictures.


Posted by: The Singing Badger Aug 7 2009, 06:14 PM

QUOTE (phase4 @ Aug 7 2009, 09:08 AM) *
Here's a rough composition of 8 pictures.


That is quite simply jaw-dropping.

Makes me long for an X-wing Fighter or suchlike, to go flying among those bizarre orbiting rockpiles.

Posted by: chemman Aug 7 2009, 07:19 PM

New Cassini ring images released by CICLOPS

ADMIN - Don't copy and paste an entire press release - just link to it.

Sorry about that, I'll keep that in mind for the future.


Posted by: Gsnorgathon Aug 7 2009, 11:28 PM

http://ciclops.org/view_event/112/Anticipation_Builds_as_Equinox_Draws_Near

They got that right! laugh.gif

Posted by: PFK Aug 8 2009, 03:35 PM

Fascinating stuff!
As a chemist I have to say if I saw an image like from a reaction set up, I'd conclude we were growing crystals at an interface wacko.gif

Posted by: ugordan Aug 8 2009, 08:16 PM

Saturn on August 5th and a large enhancement:



Looks like Saturn's night side is finally actually dark. I believe the speck above is Enceladus.

Posted by: jasedm Aug 8 2009, 09:34 PM

QUOTE (alan @ Aug 5 2009, 05:51 AM) *
ETA: moonlet with shadow in this image?
http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=196899


Well spotted Alan! this has now been officially confirmed as a ~400m moonlet orbiting just above the ring plane http://photojournal.jpl.nasa.gov/catalog/PIA11665

Posted by: Bjorn Jonsson Aug 9 2009, 03:18 AM

Having seen the recent WAC images showing Saturn and the rings where the brightness of the rings varies in the radial direction and where the brightness is at maximum 'in front of' Saturn's dayside I decided to determine the approximate Saturnshine distribution and intensity on the rings since it currently dominates due to the low solar elevation angle.

This is an unprocessed rendering showing the results. The Saturn/rings brightness ratio is highly approximate (the rings are probably too bright). In contrast, the light distribution and relative intensity within the ringsystem should be fairly accurate:




And a rendering processed to show the rings more clearly:

Posted by: ElkGroveDan Aug 9 2009, 03:41 AM

Absolutely brilliant, Bjorn.

Posted by: centsworth_II Aug 9 2009, 03:38 PM

I get a kick out of the kick you guys are getting from the new ring revelations. Can't wait to see what you think of this:

http://blogs.discovermagazine.com/badastronomy/2009/08/09/like-the-fist-of-an-angry-god/


Posted by: scalbers Aug 9 2009, 11:07 PM

The ring illumination effect shown in Bjorn's post is visible in this raw image:

http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=197996



The F-ring looks a bit brighter though, perhaps due to forward scattering of sunlight by smaller particles?

Posted by: PFK Aug 12 2009, 12:30 AM

QUOTE (ElkGroveDan @ Aug 9 2009, 04:41 AM) *
Absolutely brilliant, Bjorn.

Agreed!!
And, apologies, but I really couldn't resist tinkering with it given it evokes the vinyl format of one of my first childhood encounters with the planets many, many moons ago rolleyes.gif

Posted by: tedstryk Aug 12 2009, 11:40 AM

The ring plane crossing has of course occurred. I am looking forward to seeing what Cassini saw, but in the mean time, here is an amateur view (very impressive given the poor location of Saturn) http://alpo-j.asahikawa-med.ac.jp/kk09/s090810z.htm

Posted by: john_s Aug 12 2009, 01:39 PM

There's one http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=198002, from the day before ring plane crossing, posted so far. I don't have any inside scoop on what it shows, but it appears to be a highly foreshortened upside-down image of the south side of the rings, which were then still in daylight, centered on the point where the D ring exits Saturn's shadow but including the main rings out to the Cassini division. The remarkable thing about it is how bright the D-ring is compared to the rest of the rings- being optically thin it is not hiding in its own shadow, unlike the rest of the ring system.

John

Posted by: Rob Pinnegar Aug 12 2009, 04:36 PM

Some of the ringlets of the D ring also have a bit of orbital inclination. Perhaps this is currently helping to keep them out of the shadow of the main rings?

Posted by: john_s Aug 12 2009, 05:37 PM

Lots of ring-plane crossing ring images from August 10 and 11 are now posted. Many are difficult to figure out, though http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS52/N00140302.jpg is what appears to be the outer B-ring and Cassini division- part of a scan of the entire ring ansa. The images are very dark, as you might expect.

John

Posted by: Gsnorgathon Aug 12 2009, 09:44 PM

Based on what I've seen so far, the rings seem very flat. I'd expected to see maybe a bit of warping, but it appears not. I'd also expected more "mooms," but there don't appear to be many of those, either.

Posted by: CAP-Team Aug 12 2009, 09:50 PM

Since the rings are very flat, I'm really curious how long the actual equinox would take.

Posted by: scalbers Aug 12 2009, 10:22 PM

I think on the basis of the apparent solar diameter and the rate of change of solar declination we're talking about a day or two.

Posted by: Rob Pinnegar Aug 12 2009, 10:32 PM

I did a back-of-the-envelope calculation the other day and came up with a change of inclination of about 0.015 degrees per day. The diameter of the Sun is around 0.05 degrees as seen from Saturn, so it's a few days in total.

Posted by: volcanopele Aug 13 2009, 12:36 AM

The images for the Saturn mosaic taken earlier today have hit the ground. They are not up on the JPL raw images page, but some have been posted on the Cassini Imaging team website:

http://ciclops.org/view_event/113/Equinox_Arrives

Posted by: PDP8E Aug 13 2009, 01:55 AM

This is the Cassini equinox image referenced in volcanopele's post above (raw image 1)
I lightly rinsed it to bring out the contrast and the dark rings were hiding in the dark region in the upper left!
...and that razor of a shadow!



here is a thumbnail of the original



exciting times!

Posted by: tedstryk Aug 13 2009, 02:54 PM

One exciting thing is that currently and for the next few years, we are passing through the same Saturnian seasons that were studied by the Voyagers and Pioneer 11. Should make for some interesting comparisons.

Posted by: vexgizmo Aug 14 2009, 11:54 PM

QUOTE (Rob Pinnegar @ Aug 12 2009, 03:32 PM) *
I did a back-of-the-envelope calculation the other day and came up with a change of inclination of about 0.015 degrees per day. The diameter of the Sun is around 0.05 degrees as seen from Saturn, so it's a few days in total.

You got it right. From a Cassini friend: The entire transit spanned from AUG 09 04:00:00 UTC to AUG 12 21:00:00 UTC, with the Sun's center crossing at AUG 11 00:41:06 UTC.

Posted by: Floyd Aug 16 2009, 11:58 PM

Here is an interesting shot, N00140443.jpg, which shows a diagonal bright ridge which is angled slightly relative to the normal ring pattern. Positioned to left of middle of shot. Could it be a elongated type of propeller? The previous shot also shows this ridge, http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS52/N00140442.jpg, so I don't think it is an artifact. Images are from August 13th.


Posted by: nprev Aug 17 2009, 01:06 AM

Bizarre. A spiral density wave?

Posted by: ElkGroveDan Aug 17 2009, 02:55 AM

QUOTE (Floyd @ Aug 16 2009, 04:58 PM) *
Here is an interesting shot, N00140443.jpg, which shows a diagonal bright ridge which is angled slightly relative to the normal ring pattern.


One geometric arrangement that would account for this seeming diagonal would be a ringlet that extends out in a plane perpendicular to the main ring plain, i.e it would be a ringlet that is "taller" than the others. What might cause it? Perhaps a collision or break up of a small body in recent history, such that there hasn't been time for all the debris to settle back down to the common plane that the rest of the ringlets orbit in.

To demonstrate this, cut a long strip of paper and tape it in a loop and set it down on an old phonograph record. Bring your view down to an angle slightly just above the the plane of the record. You will notice that the upper edge of the paper to the right and left of your straight-on view seems to cross the record grooves at an angle like the image above.

Posted by: tasp Aug 17 2009, 04:19 AM

Just curious, but we have 2 data points for objects hitting Jupiter and we also know Jupiter's area and mass. Can we extrapolate a rate for objects of a given size to penetrate the Saturnian ring plane ?? And any idea how large an object it would take to make a visible 'ding' ( and I figure it depends on the depth of the ring where it hits), and I assume the math for how fast differential rotation would streak out the blem is easy (but still beyond my ken).




Posted by: Hungry4info Aug 17 2009, 04:50 AM

I doubt anything statistically significant can be determined from just two data points.

Posted by: dilo Aug 17 2009, 06:38 AM

Look at how dark is edge-illuminated A ring, compared to more diffuse F ring!


(N00140317 and 319 joined)

Posted by: nprev Aug 17 2009, 06:45 AM

Wow, yeah, really! Sure looks like the F-ring shepards scatter a lot more of that ring's material in the vertical plane. I'm sort of surprised that at least the extreme outer rim of the A-ring isn't a bit more luminous in this view.

Posted by: Greg Hullender Aug 17 2009, 01:17 PM

QUOTE (Hungry4info @ Aug 16 2009, 08:50 PM) *
I doubt anything statistically significant can be determined from just two data points.

On the contrary, if we assume the two events were independent and identically distributed, having two of them so close together tells us quite a bit. We can be fairly confident that these events occur at a rate of at least a few per century -- we'd definitely be surprised if they averaged less than one per 1,000 years and yet we somehow saw two so close together.

Of course, that doesn't tell us anything about how often rocks hit Saturn . . .

--Greg

Posted by: ugordan Aug 17 2009, 10:28 PM

Ring shot from August 15 with horrendous compression artifacts, two moons (I'm guessing Janus and Epimetheus) and a star streak:


Posted by: elakdawalla Aug 17 2009, 10:37 PM

Still pretty awesome. Goooood moooorning, all of you who live on the north side of the rings!

Posted by: nprev Aug 17 2009, 10:49 PM

Gordan, "horrendous" to you is a masterpiece to others. smile.gif Gorgeous!

Posted by: volcanopele Aug 18 2009, 01:51 AM

The moon on the left is Epimetheus, the one on the right is Janus. The star streak is HD 171391, a 5 magnitude star in Scutum.


Posted by: tedstryk Aug 18 2009, 04:31 AM

Ugordan: Beautiful!

As far as impacts, we have to remember that this recent fragment, while another data point, isn't exactly another SL-9...It is like one fairly large fragment. At any rate, while there might be some disruption, it would take something much larger than SL-9 to seriously alter the rings long term.

Posted by: ngunn Aug 20 2009, 01:02 PM

More highlighted relief casting long shadows here:

http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS52/N00141155.jpg

Posted by: Juramike Aug 20 2009, 09:39 PM

I don't know how long this effect will last, but I find this page incredibly pretty:

http://saturn.jpl.nasa.gov/photos/raw/index.cfm?start=6&storedQ=2127676

Posted by: Astro0 Aug 20 2009, 11:59 PM

I thought that this http://saturn.jpl.nasa.gov/photos/raw/index.cfm?start=9&storedQ=2127676 was nice.


Tried to keep the rings stable in the animation, so the edge of Saturn seems to jump around with the over exposure flaring, but you get the idea. Any idea which moons are seen here?

Posted by: volcanopele Aug 21 2009, 12:10 AM

'tis Tethys at bottom left.


Posted by: Juramike Aug 21 2009, 01:19 AM

Colors are fun!


Posted by: Juramike Aug 21 2009, 03:50 AM

Animation taken of chunks in Saturn's rings and their shadows rotating along. These were taken August 19, 2009 from a distance of 2.3 million km.


(GIF-click to animate)

This is from series N00141115-N00141124.jpg

(The astute observer will note a star crossing behind the bright outer F ring in the lower left corner. Might need to look at the full res version to see it.)

A full resolution version is here (2.4 Mb): http://www.flickr.com/photos/31678681@N07/3841882278/ (click on original size to view animation)

-Mike

Posted by: Juramike Aug 21 2009, 04:27 AM

Zoom of the animated GIF above. I think the chunks are being preturbed by Daphnis in the Keeler gap. You can see the ring shadows thrown across the A ring by the perturbed material.


(GIF -click to animate)

-Mike

Posted by: dilo Aug 22 2009, 09:33 AM

QUOTE (ngunn @ Aug 20 2009, 01:02 PM) *
More highlighted relief casting long shadows here:
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS52/N00141155.jpg

Animation of slides from 141155 to 161, cropped and contrast enhanced:

Clearly, also in this case there is a gravitational trig at a precise longitude for these perturbations... These shadows in the B ring vaguely recall spokes, which appear near equinox too! rolleyes.gif

Posted by: ngunn Sep 25 2009, 08:49 AM

Equinox CHARM:

http://saturn.jpl.nasa.gov/files/20090929_CHARM_Showalter.pdf

Posted by: ElkGroveDan Sep 25 2009, 01:42 PM

That's a really good slide show. Thanks. I wish I could have heard the talk that went with it.

Posted by: brellis Sep 25 2009, 02:58 PM

I've been curious about what details Northern Exposure might reveal, and I'm really looking forward to the WOW factor of a compilation of flybys before and after equinox. smile.gif

Posted by: ngunn Sep 25 2009, 03:02 PM

QUOTE (ElkGroveDan @ Sep 25 2009, 02:42 PM) *
I wish I could have heard the talk that went with it.


You will be able to when they post the audio and transcript here - usualy within a few weeks:
http://saturn.jpl.nasa.gov/video/products/MultimediaProductsCharm/

EDIT - and if the date there's correct the presentation will not happen live until next Tuesday.

Posted by: mchan Sep 26 2009, 03:23 AM

The slides on unwinding the ripples in the C and D rings to some event in spring 1984 were very interesting. I had not seen this discussed before.

Posted by: ngunn Sep 26 2009, 09:29 AM

Nor me. Fascinating stuff. That's very recent for a big event. Cassini could live to see the next one!

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