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.
Nice catch! You have just discovered 11,821 new moonlets!
(x2, rot 18 degrees, crop)
Wow - is this the region periodically disturbed by the resonance with Mimas? That would certainly help explain the chaotic appearance of that ringlet.
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
Wow, that's seriously wicked. Nice catch, Floyd!
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.
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)
Thanks sci44 for the crop and the movie. I am also surprised at how little the mini shadows change.
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.
Excellent finding, Floyd!
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..
Most of the moon shadow stuff at the moment is either from Mimas or Tethys.
Very cool animations everyone!
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'.
All I got to say is WOW, you guys...
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.
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.
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.
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.
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.
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!!!
Nice work Dan
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.
[temporarily deleted]
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.
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)..
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!!!!
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.
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... !!! )
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.
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.)
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...
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
APOD today. 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 . . .
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.
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.
Hey, that is indeed a beautiful animation of the ring particles, thanks Stu. (Best watched with the sound off though.)
The great wall of Saturn...
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.
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.
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.
More vertical relief here?
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS49/N00133497.jpg
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.
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.
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.
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.
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
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.
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
Figured it must have been something that someone from UMSF did that wiped out the image pipelines.
And an Admin person to boot.
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?
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
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.
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.
Wow...
http://saturn.jpl.nasa.gov/photos/raw/rawimagedetails/index.cfm?imageID=190390
Discuss!
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.
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.
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.
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.jpgApril 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.jpgApril 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
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
Not sure that's a moon, Steve; looks like a CR hit to me.
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.
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...
(I didn't know the Bunsen experiment, looks pretty cool!)
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.
May 9th images down. I'll post some links when I get back from Star Trek
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.
Ooooo!!!! Ahhhhh!!!! Seriously!
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.
nprev, I think its Mimas. Updated my previous post.
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
Propeller:
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136051.jpg
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS50/N00136052.jpg
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
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.jpgApril 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
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.]
Here even with my eyes it's remarkable how the 3-D aspects of the perturbations are there for us to see.
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.
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.
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.
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.
How sure are we that the perturbation is purely gravitational? Could the ring particles be colliding as a result of Daphnis's passage?
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.
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.
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
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
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.
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?
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.
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.
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
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
"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"?
http://www.nasa.gov/mission_pages/cassini/multimedia/pia07792.html
Thank you. I had missed that Cassini release in March.
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 !
Will we have enough time to watch the next wave pop up before edge-on is over?
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.
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?
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!
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
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!
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
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.
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
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.
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
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
Nope, good catch alan, that was the one I was looking for
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..
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
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
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 ) 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
Thanks chemman for very interesting resume (is a shame not to have your initial richer report!).
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.
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
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
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?
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.
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.
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):
Daphnis makes a real three-dimensional mess:
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS51/N00138916.jpg
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
That's along the edge of the B ring yes, but this is the lit face of the rings
Let me just say whoa!
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?
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.
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
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.
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.
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.
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.
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
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??
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.
http://ciclops.org/view_event/112/Anticipation_Builds_as_Equinox_Draws_Near
They got that right!
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
Saturn on August 5th and a large enhancement:
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:
Absolutely brilliant, Bjorn.
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/
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 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
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
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?
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
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.
Since the rings are very flat, I'm really curious how long the actual equinox would take.
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.
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.
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
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!
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.
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.
Bizarre. A spiral density wave?
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).
I doubt anything statistically significant can be determined from just two data points.
Look at how dark is edge-illuminated A ring, compared to more diffuse F ring!
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.
Ring shot from August 15 with horrendous compression artifacts, two moons (I'm guessing Janus and Epimetheus) and a star streak:
Still pretty awesome. Goooood moooorning, all of you who live on the north side of the rings!
Gordan, "horrendous" to you is a masterpiece to others. Gorgeous!
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.
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.
More highlighted relief casting long shadows here:
http://saturn.jpl.nasa.gov/multimedia/images/raw/casJPGFullS52/N00141155.jpg
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
I thought that this http://saturn.jpl.nasa.gov/photos/raw/index.cfm?start=9&storedQ=2127676 was nice.
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.
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.
Equinox CHARM:
http://saturn.jpl.nasa.gov/files/20090929_CHARM_Showalter.pdf
That's a really good slide show. Thanks. I wish I could have heard the talk that went with it.
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.
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.
Nor me. Fascinating stuff. That's very recent for a big event. Cassini could live to see the next one!
Powered by Invision Power Board (http://www.invisionboard.com)
© Invision Power Services (http://www.invisionpower.com)