[X] My Assistant

[nprev]

The Cassini website as well as the mass media is announcing a 'new' hypothesis on internal heating. The article also states that complex (presumably) organic molecules observed in the plumes imply an active heat source. Anybody have more details?

I still can't figure out exactly how Enceladus might have been particularly enriched in Al-26 with respect to the other icy moons, other than its proximity to Saturn during its formation...

[volcanopele]

Actually, the idea that Enceladus maybe have enriched in Al-26 is based on the shape and surface age of Iapetus. That data suggests that the Saturnian satellite system formed fairly quickly, before the short-lived radionuclides like Al-26 had decayed. For a moon with a high rock fraction like Enceladus, this helped to heat the moon to the point that it could have a molten interior. Once Enceladus had a molten interior, the current amount of tidal heating would be enough to maintain the active interior.

[nprev]

Ah...thanks, VP, figured that the "jump start" scenario probably was something like you described. Do you happen to know if Enceladus has a significantly higher mean density than the other icy moons?

Hmm...come to that, maybe this concept is more widely applicable. (Possible OT alert, here.) After all, Earth is the densest terrestrial planet, undergoes significant tidal stress, and is undeniably tectonically active...did we just get a better initial jump-start than Venus & Mars?

[stevesliva]

I'll piggyback on this Enceladus origin thread to comment that the South Pole is mentioned here:
http://space.newscientist.com/article/dn11625

[alan]

CHARM -- Enceladus: Cassini Finds Another Active World
The next "Cassini-Huygens Analysis and Results of the Mission" (CHARM) teleconference is Tuesday, April 24, from 11:00 a.m. to 1:00 p.m. Pacific Time. Dr. John Spencer presents.

60 page 5.2 MB pdf of slides:
http://saturn.jpl.nasa.gov/multimedia/prod...ARM_Spencer.pdf

[elakdawalla]

That presentation is a really valuable chronological summary of the Enceladus story. And I love those diagrams showing how all the data acquired so far (and to be acquired) maps out in space with respect to Enceladus. But I think of all the pics in the presentation, my favorite is the "action shot" of Michelle Dougherty arguing for lowering the Rev 11 flyby.

--Emily

[volcanopele]

It's sad. I'm only an undergrad and I've already been to enough of these meetings to tell who the other people in that image are just by looking at the back of their heads...

[elakdawalla]

It's Bonnie and Dennis, right?

--Emily

[volcanopele]

Yeah, I'm pretty sure that's the case.

Anyways, that is a nice presentation. Good info on the extended mission for those who haven't seen some of the details on the XM Enceladus encounters.

[Juramike]

21 km flyby?

I didn't know Cassini was also a lander.

[ugordan]

Them navigation guys better not do any of them metric-imperial conversions!

[john_s]

It's Bonnie and Dennis, right?

Yup, Bonnie and Dennis.

Um- is it just me, or are a bunch of the graphics and backgrounds messed up in the posted version of the PDF?

John.

[volcanopele]

Using Adobe Acrobat Reader 8 on a Windows machine, the file looks just fine.

[stevesliva]

Looked fine to me as well. Nice presentation!

[nprev]

Looked great to me using XP & Acrobat 7 as well.

Loved the last bullet..."you ain't seen nothin' yet"...definitely gonna hold 'em to that!

[mchan]

Enjoyed reading the presentation, john_s. Good summary of the data and hypotheses on this crazy moon to date. The XM trajectory plots on slide 58 are great in showing the flybys into the plume.

Also, no problem with graphics or background on Acrobat 7 reader and XP. Thanks!

[john_s]

Using Adobe Acrobat Reader 8 on a Windows machine, the file looks just fine.

Sigh, must be a Mac issue. Glad it looks OK to most of you folks, anyway- thanks for the feedback.

John.

[nprev]

Not at all...thanks for so generously sharing it with us!! Exciting, fascinating stuff...

[lyford]

Sigh, must be a Mac issue. Glad it looks OK to most of you folks, anyway- thanks for the feedback.

Download Acrobat Reader 8 - for some reason, Preview renders the background in grey scale.

[Rob Pinnegar]

That's a really nice presentation. It should go over pretty well.

The one thing that really surprised me is the estimate of the total mass loss over the age of the Saturn system. A fifth of an Enceladus mass! One would think that this should have noticeably distorted the shape of the moon.

[centsworth_II]

The one thing that really surprised me is the estimate of the total mass
loss over the age of the Saturn system. A fifth of an Enceladus mass!

I wonder if the results of some of this mass loss are huge ice caves
with boiling (at freezing teperatures) springs of water in their floors.

[edstrick]

"....The one thing that really surprised me is the estimate of the total mass loss over the age of the Saturn system. A fifth of an Enceladus mass! One would think that this should have noticeably distorted the shape of the moon...."

Point one: That's a pure assumption that the current rate of mass loss can be extrapolated back at a constant mass loss rate. There is a clear problem that the tidal heating calculated for the resonances Enceladus is in and could be in just doesn't add up to the current activity and heat flux.

Point 2... Enceladus is like silly-putty inside... Look at those fissure-fractured craters where the crater walls deflect the crack pattern and the crater floor is domed up with more fissures. There's a brittle shell of cold ice, and a soft layer underneath, the depth to the soft layer depending on the local heat flow. In some areas, convecting ice makes the furrowed looping texture where it's laterally deformed the crust, in others, most unusually compared with Ganymede and Europa, etc, the crust over the soft ice has just evened out isostatically, fracturing as it went.

[MarcF]

From the CHARM presentation :

"Next hi-res, hi-phase view of plume, April 24th 2007"

I'm impatient to see the pictures. Should arrive soon !

Marc.

[martin peters]

Many thanks to john_s for providing the CHARM presentation. Slide 41 shows spectra of the surface of Enceladus, the plume, and the E ring. There are 3 gaps at the same wavelength in all 3 spectra. In all cases the width of the gap appears to be about 5 data points. What caused those gaps? The way the figure is drawn at about 4.75-4.79 µm, it would appear that the flux detected coming from the E ring for about 5 consecutive spectral steps was zero, with a very abrupt transition from the continuum. Although this may be an artifact, its correspondence with a strong absorption in the spectrum of the plume at the same wavelength (and possibly with the surface, although those data points are hidden) suggests that the absorption is real.

Fig 1C of the Brown et al paper in Science 311 shows strong absorption near this wavelength in spectra of both the tiger stripes and the region near the tiger stripes. That paper does not state the center wavelengths of a pair of strong features near 4.8 µm. I measured the published figure and estimated the peak absorption to lie at 4.82 and 4.86 µm. However, when I measured Fig 3 of the same paper, showing an average spectrum of the tiger stripes, I came up with 4.84 and 4.89 for what would appear to be the same as the pair shown in Fig 1C.

Although these absorption features possibly are time variable, it seems more likely to me that the variation is due to my error in measuring the figure. The juxtaposition of the peaks of the feature in the plume and in the E ring in CHARM slide 41 suggests that there is a real feature in the range 4.75-4.79 µm.

martin

[Rob Pinnegar]

Point one: That's a pure assumption that the current rate of mass loss can be extrapolated back at a constant mass loss rate.

Yup, no argument there. It's analogous to estimating the Moon's age based on its current rate of recession from the Earth.

[remcook]

here you go

http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=108492
etc

[ugordan]

Wow, look how one of the plumes is readily apparent in even this short exposure frame: http://saturn.jpl.nasa.gov/multimedia/imag...iImageID=108482

Amazing. That's really some dense plume, curiously it's not so readily visible in other clear filtered frames. Reminiscent of NH's recent Io shots.
It's as though there was a violent outburst at that point in time, either that or the polarizer filter really brings out the plumes.

[Exploitcorporati...]

Indeed very reminiscent of recent views of Io...a quick summary:

[Tom Tamlyn]

Sigh, must be a Mac issue. Glad it looks OK to most of you folks, anyway- thanks for the feedback.

No problems that I noticed with Adobe Acrobat Standard (application, not the reader) v. 7.0.9 on my Mac, running OS 10.4.9.

Thanks for sharing your extremely interesting presentation.

TTT

[belleraphon1]

CHARM -- Enceladus: Cassini Finds Another Active World
The next "Cassini-Huygens Analysis and Results of the Mission" (CHARM) teleconference is Tuesday, April 24, from 11:00 a.m. to 1:00 p.m. Pacific Time. Dr. John Spencer presents.

60 page 5.2 MB pdf of slides:
http://saturn.jpl.nasa.gov/multimedia/prod...ARM_Spencer.pdf

A wav file and word doc transcript are now available for this presentation.

wav (25.6MB) http://saturn.jpl.nasa.gov/multimedia/prod...ARM_Spencer.wav

doc http://saturn.jpl.nasa.gov/multimedia/prod...nscript_raw.doc

Myself, have not listened or read yet... just noticed these...

Enjoy

Craig

[climber]

They're talking of 30 kms fly by now :
http://www.space.com/news/070801_cassini_update.html

[volcanopele]

While the flyby will bring Cassini to within 30 km of Enceladus' surface, the encounter will occur over the southern low latitudes, not right over the plume. However, shortly after the encounter, the spacecraft will fly through the plume, just not at that close of a distance. Not sure what the C/A to the south pole will be, though I think it is further than the 100 km encounters over the south pole in the XM.

[belleraphon1]

All....

While I can understand the temptation to sample the gases and particles coming from the plumes, I wish they had scheduled this close a flyby AFTER the prime mission was completed.

I know CASSINI has to dive through at least the E-ring plane on each orbit.... but...

To those who are more knowledgeable... how risky is this?

Craig

[ugordan]

I'm more uneasy about the navigation uncertainties than small icy particles. If it's indeed mostly very small water ice particles, they'll flash into vapor at contact so no hazard to the spacecraft there. Coming as close to Enceladus as 30 kilometers on the other hand I find quite scary to be honest.
Rest assured, though, the mission folks will assess every risk there is and if they give the go-ahead, it means the risk is low.

[belleraphon1]

Thanks ugordan.....

really, no one can predict the unpredictable...... I will just have to white knuckle it next March.

Craig

[belleraphon1]

All...

the sublimation model has been refined.

http://www.spaceref.com/news/viewpr.html?pid=23264

Make this March 08 encounter all the more interesting.

Craig

[brellis]

Does anybody know where to find a transcript of yesterday's (16 August 2007) von Karman lecture on Enceladus?

thanks,


Brad