All.....

http://saturn.jpl.nasa.gov/news/press-rele....cfm?newsID=816

"Roger Clark of the U.S. Geological Survey in Denver goes further, saying, "We see the same spectral signature on all the moons that have coatings of dark material." Clark is lead author of one of the new papers, which focuses on Saturn's moon Dione. His team found the dark material there to be extremely fine-grained, making up only a very thin layer on the moon's trailing side. Its distribution and composition, as measured by the Cassini visual and infrared mapping spectrometer, indicate that the dark material is not native to Dione. And scientists see many of the same signatures there that appear on the moons Phoebe, Iapetus, Hyperion and Epimetheus, and also in Saturn's F-ring.

As for where this material comes from and what the dark material is, Clark said, "It's a mystery, which makes it intriguing. We're still trying to find the exact match." The visual and infrared spectrometer detected unique absorption bands in the dark material within the Saturn system, which scientists have not seen anywhere else in the solar system. "The data keep getting better and better," he said. "We're ruling things out and figuring out pieces." So far, the team has identified bound water and, possibly, ammonia in the dark material.

Clark's team reports tentative evidence to support the hypothesis presented earlier this year that Dione is still geologically active. In one series of observations, the infrared spectrometer detected a cloud of methane and water ice encircling Dione in its orbit within the outer portions of Saturn's E-ring."

And

"A paper led by Frank Postberg of the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, says there are traces of organic compounds or silicate materials within the water ice-dominated E-ring, close to Enceladus. "

Lost my online access to Icarus.... darn!!!!!

Craig

Thanx for the post.

It did seem to have a ring of familiarity, though . . . .

Epimetheus! I'd heard plenty of theories about a Phoebe/Iapetus/Hyperion connection, but never as far in as Epimetheus. Very interesting. If they keep finding this stuff, it might be more informative to make a list of placed that DON'T have the dark stuff.

Doesn't this have a rather negative effect on the theories that Iapetus' dark face is simply that moon's natural surface after white snow-like frost has been sublimated off?

If the dark stuff is of similar composition all around the Saturn system, then you'd have to think it was all emplaced exogenously via some form of a mantling process, wouldn't you? Doesn't that fly in the face of what the "experts" had decided was going on at Iapetus?

Doesn't surprise me, though -- Iapetus still looks like its dark stuff was exogenously deposited to me. I've never been convinced by the strip-off-the-white explanation for a majority of the darkened Iapetan surface.

-the other Doug

As I understand it there is a distinction between the the thin exogenous dusting of dark reddish stuff (seen on both dark and light areas of Iapetus) which is alleged to have provided the asymmetric trigger for the thermal feedback, and the majority of the dark material in the dark areas which is interpreted as sublimation residue. I can't access Icarus, and I can't divine from the press release which of the two is being compared to the dark stuff seen on the other moons. Can anyone clarify this?

Interesting to see this article - perhaps I can drop in the library at work and take a look. I recently made a related comment in the "2007 Tethys Imaging" thread, wondering whether its darker material, apparently in a band on the leading hemisphere centered on the equator has any similarities to Iapetus. My most recent Tethys map helps to illustrate the location of this dark material. Do these papers also discuss Tethys?

Isn't the dark material on Dione centered on the trailing hemisphere? If this is the case, and the dark material on all the moons has a common origin, then the large-scale exogenic event (whatever it was) probably ended a long time ago. Otherwise, Dione's leading hemisphere would be at least somewhat covered by now. Another possibility is that Dione has had recent geological activity that is for some reason resurfaced more of the leading hemisphere in brighter material.

But the idea of an old source contradicts the general consensus regarding the source of Iapetus's dark side. Such is the pleasure of mysteries.

I know!!!!!!

The toddlers in the day-care-of-the-gods did it with airbrushes!

I note the 'coloration shift' from east to west on Iapetus, to me, implies in situ 'processing' of a 'feedstock' material of exogenous origin.

That this 'feedstock' material can 'leak' (in relative to Iapetus, minute quantities) out of the primary transport mechanism to Iapetus and appear in traces on other moons doesn't, upon reflection, to seem too surprising.

Not sure the extra deep craters of Hyperion are 'burned into it's carcass', but rather existing craters have been sites were the processing of the exogenous materials is enhanced. That the (distant) sun's rays are 'focused' onto the crater floors virtually globally on Hyperion, and the object is believed to 'chaotically' change its' orientation to the sun over time, again, to me, strongly suggests a 'catalytic' property of the solar efflux on this exogenous material in 'darkening' (or 'developing' to borrow a word from the folks at Kodak) it for us to then study.