Starship Asterisk*

Not knowing the lighting conditions during sightings of the mysterious "spokes" in Saturn's rings (APOD 27 Nov '06), I can't help wondering whether they might be some sort of shadow phenomenon, perhaps caused by an object or objects slightly out of the rings' plane? Just a first thought. Suppose others have already checked it out and rejected it?

Looks like a giant ghost of Harvey the rabbit, or a man in rabbit costume, if you look closely

I agree with Smitty up there. I think they are reflections of the planet's surface, something akin to tricking the lens phenomena. Just recently on spaceweather.com, a photo was published of city lights reflecting off ice crystals in the upper atmosphere.

http://www.spaceweather.com/swpod2006/2 ... avais1.jpg

Ta152h0, that is an amazing picture. I have never seen anything like that before. I didn't even think something like that was possible.

Two ideas cross my mind regarding this massive centrifuge-
The uneven particle distributions caused by collisions makes uneven light reflection.
While the rings reflect light, some particles (ice?) would bend the light together or refract.

I was under the impression that the spokes had been identified as being associated with Saturn's magnetic field.
One of the Galileo researchers, (She may have been on another probes team), had done some statistical analysis and showed a direct correlation with the spokes and the planets magnetic field. I can only guess what the causal relationship is though. Perhaps static buildup?

Here's a good discussion:
http://www.nature.com/news/2006/061120/ ... 20-14.html

The ladies name btw is Caroline Porco. She first looked at the spokes back in the Voyager days.

Rather than spokes, the ghostly image resembles a bunny rabbit looking toward the camera. The spokes are in the position of the rabbit's ears.

The spokes in Saturn's Rings have been a matter of significant interest since the days of Voyager when they were first imaged. Carolyn Porco, the lead of Cassini's Imaging Team, has written about them many times. (See http://www.ciclops.org for up-to-date info on the Cassini project).

Excerpts from Carolyn's writings.....

"Although their formation is still a subject of inquiry, scientists are confident that the microscopic spoke particles are slightly electrically charged and therefore are influenced by Saturn’s magnetic field."

and

"The Sun-ring-spacecraft viewing angle makes quite a difference in the spokes’ appearance: they appear bright against the rings when seen at high phase angles and darker than the rings at lower phase angles. This view was acquired at a phase angle of 133 degrees."

Perhaps this is an Aurora like phenomenon produced by the collision of charged particles contained in the Sun's Solar wind with Saturn's rings.

ta152h0 wrote:I agree with Smitty up there. I think they are reflections of the planet's surface, something akin to tricking the lens phenomena. Just recently on spaceweather.com, a photo was published of city lights reflecting off ice crystals in the upper atmosphere.

http://www.spaceweather.com/swpod2006/2 ... avais1.jpg

ta152h0(wolf)
Are there more of these images around? It would make a great APOD.

BMAONE23 wrote:

ta152h0 wrote:I agree with Smitty up there. I think they are reflections of the planet's surface, something akin to tricking the lens phenomena. Just recently on spaceweather.com, a photo was published of city lights reflecting off ice crystals in the upper atmosphere.

http://www.spaceweather.com/swpod2006/2 ... avais1.jpg

ta152h0(wolf)
Are there more of these images around? It would make a great APOD.

Agreed. I can look north and south from my house and see the clouds glowing from the cities on both sides of me, but I've never seen anything like that picture.

However, I don't think mere reflections are sufficient to explain Saturn's spokes, because there's no distinct features to be reflected. Something seems to be actually causing disturbances of the rings, and the magnetic field idea sounds feasible. I remember reading a few years back that Saturn has a complex magnetic field which made it difficult to make consistent measurements of the rate the bulk of it's mass rotated at.

In this latest image of the Spokes of Saturns rings http://www.nasa.gov/mission_pages/cassi ... 08831.html
it appears that the dark spokes are shadows of the lighter toned spokes that are cast on the rings. Almost like the lighter material is above the ring plane and casting shadows on the rings.

Actually, the key here is in the caption:

This "difference image" is actually a composite of two images of the B ring, taken about 45 seconds apart. The view illustrates how the several spokes imaged here moved between exposures. The spokes were bright against the rings in both original images, but the brightness of the earlier image was reversed so that the spoke movement is easy to discern. The "dark" image of the spokes was taken first, thus rotation in the scene is toward the bottom.

So the dark spokes are the same ones as the light, but color adjusted to emphasize changes over time.

The caption also mentions one of the spokes being about 600 km wide. It appears to have moved by it's own width in 45 seconds, so that's about 48,000 km/hour. This is roughly consistent with the velocity of some of Saturn's inner moons, so the spokes do not appear to migrate through the ring material. Also, the caption notes that the older spokes shear as they rotate due to the higher orbital velocity at lower altitudes.

All this is consistent with the spokes being an effect occuring to the material of the rings, such as polarization or disturbances by a meteoroid or tidal forces.