Printable Version of Topic

Posted by: edstrick Nov 4 2005, 11:59 AM

Ooooh!.

I was brousing the last 500 "raw" images and spotted an overexposed F-ring shot with a trace of G-ring, so I contrast-stretched it to see more.. there was something in the foreground...

Then I decided to contrast a badly auto-contrast stretched Saturn nightside image.

Posted by: Phil Stooke Nov 4 2005, 02:46 PM

edstrick, your 'something' is Janus.

Phil

Posted by: edstrick Nov 5 2005, 10:51 AM

Phil: Thanks. I didn't go back and check.

Here's 3 more from the F-ring "movie"
#42291 is also one of the inner "potatos" in front of the rings. In both of these shots, this and #42321, the part of the moon's nightside that is not illuminated by a crescent Saturn is darker then the background. There clearly is a "glow" behind these moons that is not scattered light from the F-Ring in the camera, but is an extended halo of the rings that I'm not sure has been this clearly seen before. (There was one crescent ?Thethys? series some months back that also had a bright background glow behind the moon.) Note you can also see the G-Ring.

#42273, 42269, and 42312 all have crescent moons behind the rings, with most of the nightsides illuminated by Saturn shine.

Finally, in a recent series of "E-Ring" wide angle images, W00012012 is maybe the best example, what I expect is Enceladus appears to have a bright fringe on the nightside silhoueted against the E-ring glow that I'm inclined to think is not jpg artifact. All the images in this sequence that are well enough exposed to show the brightness difference between the nightside and the E-ring without wiping out the nightside show it. It looks real, but the horrible compression artifacts in these 512 x 512 wide angle images leave me mentally flipping back and forth.

Posted by: edstrick Nov 5 2005, 10:56 AM

Oh.. also. In the well exposed images in this series, the midplane of the E-ring appears DARKER then the ring just above and below the midplane. Beyond this bright zone of the E-ring that I presume is at Enceladus' orbit, the ring brightness descreases, but this dark centerline disappears faster than the ring fades. To the left, towards Saturn, the ring brightness drops somewhat, it doesn't widen, so we're nearly in the ring plane..... and the faint dark band pretty much disappears!

"Go Figure!"

Posted by: dilo Nov 5 2005, 02:51 PM

Stunning images, apart the "quantization" artifact... so I worked on them to have smoother realistic gradients. Enjoy!

Posted by: Joffan Nov 6 2005, 04:32 AM

Is that the ring's atmosphere that we can see giving a wedge of light or is it an imaging artifact?

Posted by: edstrick Nov 6 2005, 07:52 AM

I presume it's not a gas atmosphere, but rather micrometer or smaller sized dust, down in the size range where it can be electrically charged by radiation or photoelectric effect, then moved out of the ring plane by magnetic field effects. That's what I believe is1 the explanation of the diffuse halo around Jupiter's rings.

And, Dilo, that did nicely improve the cosmetics of the images without blurring detail in the more adequately exposed parts. Nice.

Posted by: dilo Nov 6 2005, 07:58 AM

This is exactly what I tried to do... thanks!

Posted by: dilo Nov 10 2005, 02:54 AM

Another enhanced view (from last published raw img); here rings are almost edge-on and their inclination/position seems a little bit "odd"....

Posted by: jamescanvin Nov 11 2005, 12:40 AM

That's a great image dilo, unusual geometry, thanks.

I love the ring-shine onto Saturns night side

James

Posted by: ugordan Nov 11 2005, 08:02 AM

Personally, I don't think the halo around the rings (main rings at least) is real, it's more likely scattered light in the camera optics. If you take any NAC image of a bright or well-exposed target and stretch the contrast, you'll notice the same ghostly halo. It's either perfectly normal or as if there's still some haze left on the NAC optics that hadn't been removed. I've seen the same halo even around Jupiter images taken before the haze anomaly so I take it the most probable reason is the light bouncing off the CCD back onto the shutters/filters/support structures and back again to the detector, though this is probably a low order effect.

Posted by: edstrick Nov 11 2005, 10:06 AM

Ugordan:

I know all about the scattered light problems. It definately doesn't help. but you can see the nightside of Janus and the other small moon <Epimetheus? Prometheus?> in silhouette against the glow as *darker* than the background. That portion of any glow MUST be behind the moon, not in the camera.

Posted by: ugordan Nov 11 2005, 10:48 AM

I can see your point. There certainly seems to be material behind the small moons, but do note that they're visually near the F ring which is not very narrowly contained, I don't know if the G ring is inside their orbit OTOH so that could also be a factor. However, I believe the majority of the glow is due to scattered light, it would be much more favorable if Cassini was almost aligned with the ring plane, cutting scattered light to a minimum. That would certainly make a more convincing case.
In the two images of the small moons it's clearly visible that the glow appears to be at its thickest around the main rings and not spread along the width of the scene as one would expect if the material was outside the main rings (F,G rings), but still in the ring plane. THAT part of the glow I believe is optical artifact and not real and it could be misinterpreted as a sign of significant amounts of material above and below the main rings.

Posted by: Ames Nov 11 2005, 10:59 AM

The glow is definately in the background

Nick

Posted by: edstrick Nov 11 2005, 11:39 AM

And you can see the G-Ring just above and partially behind the moon.