[X] My Assistant

[ngunn]

More vertical relief here?
http://saturn.jpl.nasa.gov/multimedia/imag...9/N00133497.jpg

[ugordan]

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.

[Bjorn Jonsson]

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.LINK

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.

[ugordan]

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.

[ngunn]

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/imag...7/N00128822.jpg

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

[Floyd]

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.

[chemman]

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%20Arti...nis/daphnis.PDF

Cheers

[elakdawalla]

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

[Floyd]

The Looking Ahead Rev109: April 16-May 2 (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

[ElkGroveDan]

guess the image pipeline from Saturn is no better than from Mars at he moment.

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.

[Floyd]

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

[Floyd]

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%20Arti...nis/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.

[Floyd]

This picture, 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?

Attached image(s)

 

[dilo]

This picture, 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 these 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.

[Bjorn Jonsson]

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

http://saturn.jpl.nasa.gov/photos/raw/rawi...?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/rawi...?imageID=190230