[X] My Assistant

[alan]

Six days to go until Enceladus flyby ( E2? ) at 175 km

[john_s]

Can I just say how impressed I've been with Emily Lakdawalla's coverage of Cassini on the Planetary Society Web site?

[TheChemist]

Quite an impressive U-turn from Dr. Spilker. I thought only politicians could pull these up

[Guest_BruceMoomaw_*]

The real story turns out to be, apparently, that Spilker stated so forcefully to Ms. Lakdawalla that the Cassini science team was certain that "The vents are not the source of the E Ring" that Ms. Lakdawalla jumped to the conclusion that the team had actual chemical-composition evidence to that effect. After which I jumped to the conclusion that she must have actually drastically misquoted Spilker in that line. In short, we both jumped to false conclusions as a result of the Cassini science team jumping to its OWN (seriously dumb) false conclusion immediately after the flyby, and then reversing it later.

[craigmcg]

I agree that the articles on the planetary society site are excellent. I hope to see many more like them!

It's good to see that whatever misunderstandings took place along the way, the facts (for lack of a better word to describe our present knowledge) are coming to the forefront.

[Guest_BruceMoomaw_*]

I will definitely go along with that. (I'll also go along with the statement that Ms. Lakdawalla's Planetary Society articles -- despite that one mistake -- have been excellent, and extremely useful to me personally.)

Now, then. Since it does seem highly probable that the E Ring particles are being expelled by Enceladus' vents, what are we to make of the sudden dramatic eruption observed by Cassini during its final approach to Saturn, which doubled the E Ring's total vapor mass for a few weeks before it dropped back to normal? We seem to have, just from this incident, proof that the vents are not just trickling out vapor at a very low constant rate, with the E Ring particles having a very long lifetime. Is the team looking for evidence in the Enceladus photos of a very recent venting event? It would seem the logical thing for them to do.

[elakdawalla]

Can I just say how impressed I've been with Emily Lakdawalla's coverage of Cassini on the Planetary Society Web site?

Aw, shucks. Thanks, everyone. It's a labor of love.

Thank you, Mr. Moomaw, for being willing to retract your statement publicly.

And don't be hard on Linda Spilker, everyone, she deserves a lot of credit. When she was talking to me it was still relatively soon after the flyby. Linda may be the Deputy Project Scientist but Cassini has an ENORMOUS science team involving twelve different instruments, and it takes a long time for the team -- even someone as involved as she is -- to synthesize what all of the myriad different data sets are telling you. I'm happy she was willing to talk with me and express her own excitement about what were then very premature and uncertain conclusions, rather than sitting and waiting and waiting to talk about anything until all the "i"s were dotted and "t"s crossed. Of course the story changes over time -- that's what the scientific process is about. It's exciting to be able to watch the story unfolding.

Linda told me today that part of the confusion is because the CDA team were confused about the implications of their own data right after the flyby (something about the timing of the observations or something, I'm not quite sure about the details). She also told me there's a CDA release coming out shortly that should clear some of this up, but that it's being held up because NASA HQ doesn't want to confuse the press with more than one story at a time, and the Shuttle trumped everything. That's a tale of woe I've heard before from many missions. I wish NASA would give us more credit, and respect that we can handle more than one story at a time!

Emily

[dvandorn]

I wholeheartedly agree with your sentiment, Emily. But we have to face the fact that we live in the world of the sound bite, the news cycle, and the MTV attention span.

Those of us who enjoy news of planetary exploration generally have longer-than-average attention spans and an ability to retain interest in a subject for longer than a single news cycle. But, more and more, I've come to the conclusion that we're the exceptions. Of course, we have resources like this forum with which to supplement what the organized media offer, and without it I think most of us would be going slowly insane...

As for my own two cents -- I'm glad to have both you and Bruce as contributors to this forum. I know that, even though you both write for special-interest publications, you have to keep your professional work at a certain level. Whereas here, y'all can get as detailed and as esoteric as you want, and anyone who wants any further background to help them understand just asks for clarification. It's refreshing and vastly more satisfying (to me and, I suspect, to a lot of the people here) than any other newsgroup, chat group, forum or single publication could hope to be.



-the other Doug

[pioneer]

I didn't know Emily Lakdawalla became a member

Glad to have you join us.

[malgar]

A view of Enceladus cracks.

[tedstryk]

Great work!

[Guest_BruceMoomaw_*]

Two new notes on the E Ring from the new "Dust In Planetary Systems" abstracts ( http://www.lpi.usra.edu/meetings/dust2005/pdf/program.pdf ):

(1) In absract #4047, Cassini's CDA "found that the particles predominantly consisted of water ice (manifesting itself in the TOFMS as hydronium ions, with varying numbers of water molecules attached) and minor silicate impurities." If the E Ring particles really are made of water vapor spewed out of Enceladus' vents and then refreezing, where did even those small amounts of silicates come from? Is the speed with which material is sprayed out of the vents fast enough to propel small bits of Enceladan rock to the moon's escape velocity? Or...

(3) ...Is it possible after all that the E Ring does consist of material blasted off Enceladus by meteoroid impacts? Paper #4059 reports the results of simulations based on the assumption that this is the cause, with Enceladus and Tethys as the only sources -- but, once again, it never provides any explanation of why meteoroids would only spatter material off those two moons and not the others. One interesting note, though: in these simulations Tethys provided fully 30% of the E Ring material -- "a dust supply necessary to explain the large extent of that Ring and also the additional density hump near Tethys' orbit seen in ground-based [Keck] observations."

[dvandorn]

Maybe we're seeing a snapshot in terms of the E ring -- in other words, maybe it usually consists of mostly water ice derived from Enceladian venting, and it's been recently enriched with silicates from an impact at Tethys? As time goes on, the water ice will continue to be replenished, while the silicates might sort out?

I'm just trying to point out that we tend to observe things and assume that they're in some type of steady state -- not changing much over time. Perhaps we're seeing the E ring in a far different state than it was, say, 30 years ago, and that it'll be in a different state in another 30 years....

-the other Doug

[Guest_BruceMoomaw_*]

Damned if I know. It would seem to contradict Occam's Razor; but then, if you shave often enough with Occam's Razor it occasionally cuts you.

In any case, any explanation of the E Ring must explain that huge eruption Cassini saw 5 months before its arrival at Saturn that doubled the E Ring's vapor mass instantly -- and then completely faded away in a few weeks. Either that was one hell of a big impact on something, or one hell of a big eruption of material from Enceladus (or Tethys). Which is more likely? The latter, I suspect.

[Decepticon]

WOW! Nice Update!

North and South Polar projections.

http://ciclops.org/view_event.php?id=27

[djellison]

Jason - are you trying to say something about this fair isle

http://ciclops.org/view.php?id=1381



Nice pic from Modis on either Terra or Aqua though - I have one a bit like that, but a bit clearer - printed really large on my wall - you can make out Leicester quite clearly - and infact you almost can on that tiny version of it

Doug