[X] My Assistant

[volcanopele]

There was a news briefing at AGU this afternoon covering the results of the Enceladus flybys this fall:

Saturn's Dynamic Moon Enceladus Shows More Signs of Activity
http://saturn.jpl.nasa.gov/news/press-rele....cfm?newsID=889

The imaging team has released several image products showcasing the results from the encounter:
http://ciclops.org/view_event/98/Enceladus_Shifting_Terrain

I do hope you all enjoy the two large mosaics that accompany this image release:

Tiger Stripes...Magnified!
http://ciclops.org/view/5409/Tiger_StripesMagnified
http://photojournal.jpl.nasa.gov/catalog/PIA11135

A Tectonic Feast
http://ciclops.org/view/5310/A_Tectonic_Feast
http://photojournal.jpl.nasa.gov/catalog/PIA11133

I guess the big results from ISS is the "new" theory that the tiger stripes are analogous to the mid-ocean ridges on earth, spreading centers that act as axes where new terrain is produced.

[dvandorn]

When I finally figured out (with Phil's appreciated help) that Jason was speaking of tectonic compression features, I felt sorta stupid. Well, we all have days like that...

I guess one of the $64,000 questions here is the length of time we think this particular era of crustal spreading has been going on. And to have any real idea of the amount of new crust formed in a given timeframe, we need to know how fast the spreading is taking place. I think we may lack the data to confidently answer either of those questions.

However, you can toss assumptions into the equations, and get ideas of various ranges. That lets you put together a variety of models, which you can then figure out how to test.

If compressional forces are piling up a very thick mass of hard ice in a given region, and yet we don't seem to see constructional forms (i.e., mountain ranges or big, obvious bulges), we've got to conclude that the thickest part of the pile is sinking into an elastic mantle. It may not be subducting as a plate under another plate, but if it's being recycled into the mantle, it's at least a subduction-like process.

I'm not sure that it's actually melting into the mantle. I think we may have a somewhat unique "warm ice" process going on at several places in the mantle, where the material is solid but has elastic properties. I have no idea when or how the phase change from either amorphous or crystalline water ice to this warm ice with elastic properties takes place -- I'm not even sure the physics of that proposed state of ice are all that well thought-out right now. (Obviously, if anyone has any references to the current thinking on the subject, I'd love to see them... )

But I think we need to know more about properties of the Enceladan mantle that underlies such subduction-like processes before we can model what's happening, how long it's been happening, and how fast it's happening. And as much as I'd enjoy getting enough information to answer these questions, I'm not positive that Cassini is capable of gathering enough of the right kind of data to do so.

-the other Doug