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Unmanned Spaceflight.com > Outer Solar System > Saturn > Cassini Huygens > Cassini general discussion and science results
Bjorn Jonsson
Spoke-like features are visible in several recent wide angle images of the rings:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=80037
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=80036
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=80034

These are high-phase views so any spokes should be brighter than the rings. And indeed there is a bright, narrow, vertically elongated feature visible in the B ring in several images that *might* be spokes. On the negative side there's this:

http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=80041
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=80031
http://saturn.jpl.nasa.gov/multimedia/imag...eiImageID=80032

Nothing obvious here so the spoke-like feature might be due to something else, for example scattered light within the camera - it's suspicious that the camera is pointing in a slightly different direction in these images. Another possibility is that the images were obtained at different times - the spokes vary with time. It will be interesting to see if these features are spokes or not.
edstrick
I'm inclined to think the feature in the first set of images is indeed a spoke. It's got a "reasonable looking" geometry for a spoke and can't be the zero-phase-angle brightness surge (which is circular, anyway). This is a bright, well exposed image, not a low-light super high phase image, and there are no obvious scattered light artifacts outside of the rings.
ugordan
I've also noticed the feature. It indeed appears this is a spoke. If you look really, really closely you can see the same feature in the 4-image sets taken before (your second set) and after, they progress on their orbital paths. Upon inspection of frames in the single set (the most visible one, ring ansa), prograde motion (clockwise) can be discerned as well. I'll try enhancing the spoke once I get back home from work if somebody doesn't beat me to it.
Bjorn Jonsson
Following the initial excitement I took a more careful look at the images and yes, a spoke is probably visible in three image sets (very faint in the first and last image):

Click to view attachmentClick to view attachmentClick to view attachment

Prograde movement is apparently visible and seems roughly constant throughout these three image sets. If this imaging sequence is comparable to visually similar sequences I've seen in the PDS images the time between these frames is roughly constant as well.

Quick-and-dirty processing of the W00016454.jpg image reveals some details but also brings out some JPG artifacts (I suspect these images may have been compressed aboard Cassini using lossy compression as well):

Click to view attachment (a simple contrast stretch)
Click to view attachment (unsharp mask)

One thing that makes me a bit suspicious is the fact that the spoke (?) appears exactly vertical. A coincidence or scattered light ?
Bjorn Jonsson
QUOTE (Bjorn Jonsson @ Jul 25 2006, 12:23 PM) *
One thing that makes me a bit suspicious is the fact that the spoke (?) appears exactly vertical. A coincidence or scattered light ?

And to reply to myself the CICLOPS site has now confirmed that this is indeed a spoke: http://ciclops.org/view.php?id=2121
AlexBlackwell
QUOTE (Bjorn Jonsson @ Jul 25 2006, 01:53 PM) *
And to reply to myself the CICLOPS site has now confirmed that this is indeed a spoke: http://ciclops.org/view.php?id=2121

I thought I would chime in so people don't wonder why you're talking to yourself laugh.gif

Nice work, Bjorn.
The Messenger
Uh, isn't a spoke supposed to have a little more structure? This looks way to much like the reflective sheen of an LP record - a very rough refractive grating. Is this what the spokes are supposed to be?
Ian R
Great work Bjorn! cool.gif
Roby72
Hello all !

new images on the Raw site (images W00016526-29) has shown further spokes seen together in my small animated gif.
smile.gif

Robert
Roby72
another short spokes movie !

Robert

(W00016515-518)
ugordan
Very nice Roby. Those are definitely spokes. Once calibrated and flatfielded, these images will be much clearer, but we can already be fairly certain we're seeing spokes.
I'm puzzled by one thing though -- the spokes in your movie are rotating clockwise, while they should be rotating counter-clockwise from Cassini's current vantage point. Are you sure you didn't assemble the sequences backwards?
The Messenger
Is Saturn rewinding? smile.gif
Roby72
rolleyes.gif No, Saturn turns right, that means counterclockwise when seen from the north Pole. This view is from beneath the ringplane from the south - the sun illuminates this side of the rings (see pic from solarsystem simulator) The result from this geometry is, that the rings rotate counterwise. Currently Cassini sees the unlit side of the rings.
Unlit side - bright spokes,
sunlit side - dark spokes

Hope this helps.

Robert
Bjorn Jonsson
QUOTE (Roby72 @ Jul 28 2006, 10:34 PM) *
Currently Cassini sees the unlit side of the rings.

Correct but a bit confusing in this context because these specific images show the lit side of the rings as you noted. In addition, some of the apparent motion of the spokes may be due to changing camera angles throughout the imaging sequences. But they definitely move clockwise - to confirm this I also made a spoke movie.

Also the spokes do not always appear dark when viewing the lit side. When viewing the lit side they appear bright at high phase angles (or at least brighter than the rings) since they are composed of very small particles. The images in the first message of this thread illustrate this nicely.
ugordan
QUOTE (Roby72 @ Jul 28 2006, 11:34 PM) *
rolleyes.gif No, Saturn turns right, that means counterclockwise when seen from the north Pole. This view is from beneath the ringplane from the south - the sun illuminates this side of the rings (see pic from solarsystem simulator) The result from this geometry is, that the rings rotate counterwise. Currently Cassini sees the unlit side of the rings.

There -- you figured it yourself, Cassini is seeing the unlit side which means it's above the ringplane, the sun is shining from below. If it's above the ringplane --> the rings rotate counter-clockwise.

QUOTE (Roby72 @ Jul 28 2006, 11:34 PM) *
Unlit side - bright spokes,
sunlit side - dark spokes

It's not as simple as that. Spoke appearance varies with phase angle and at high phases the contrast can be reversed. Such as it case here.

EDIT: Ah, never mind that. I thought these sequences show the unlit side of the rings when in fact it's the lit side. The contrast confused me a bit. Clockwise it is, then.
dilo
This new movie of unlit side was taken with different filters, all in the IR/red (half size, enhanced contrast):
Click to view attachment
note anticounter-clockwise movement also in the rings texture ohmy.gif .
The Messenger
You know, there are some rather highly reflective moons hanging around. Are we sure the spokes are not enlongated reflections and/or shadows from these Fresnelly-challenged objects and rings? What does moonlight reflecting off a ring look like? The spoke papers mechanisms I have perused don't seem to correlate with the bulk movement I see in the spokes...if I am correctly interpreting what the spokes 'are'.
dilo
QUOTE (The Messenger @ Aug 4 2006, 12:06 AM) *
You know, there are some rather highly reflective moons hanging around. Are we sure the spokes are not enlongated reflections and/or shadows from these Fresnelly-challenged objects and rings? What does moonlight reflecting off a ring look like? The spoke papers mechanisms I have perused don't seem to correlate with the bulk movement I see in the spokes...if I am correctly interpreting what the spokes 'are'.

Interesting observation, IMHO seems very improbable we are seeing moons reflections...
However, I do not know very well the spokes theories. Do them should appear brighter in the unlit ring side, as we see there? (they should if made of very thin particles...)
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