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Fraser
2007-Mar-13, 09:48 PM
Since Cassini arrived at Saturn, it has made many impressive discoveries. One of the most intriguing is the discovery that Saturn's icy moon Enceladus has geysers spewing water ice into space. ...

Read the full blog entry (http://www.universetoday.com/2007/03/13/radioactive-core-might-explain-geysers-on-enceladus/)

Jerry
2007-Mar-14, 01:28 PM
There is an obvious balancing act here: If the original conglomerate was so radioactively hot, there had to be a tremendous amount of moisture to start with. Why if this scenario was true, you would have to expect Saturn to be wringing with water:)

dhd40
2007-Mar-14, 04:41 PM
There is an obvious balancing act here: If the original conglomerate was so radioactively hot, there had to be a tremendous amount of moisture to start with. (SNIP)

And why is Enceladus the only radioactively hot moon in our solar system? All the other active moons are ONLY gravitationally hot (Io, etc) !?

Jerry
2007-Mar-14, 07:06 PM
ALWAYS a problem for virtually any explanation for what we are witnessing at Enceladus - especially compared to Saturn's other moons. Does Enceladus have an exclusive history? Another question: Are other moons strictly gravitationally heated? There is intense electromagnetic activity between Jupiter and Io - and what about Triton?

Grand_Lunar
2007-Mar-14, 07:10 PM
I would have thought that gravitational action was causing the moon to spew out water.
I wonder if that hypothesis was considered.

01101001
2007-Mar-14, 07:27 PM
I would have thought that gravitational action was causing the moon to spew out water.
I wonder if that hypothesis was considered.

How? The gravity squeezing Enceladus like a ripe grape?

I think first there was: NASA: Enceladus "Cold Geyser" Model (http://www.nasa.gov/mission_pages/cassini/multimedia/pia07799.html)


Some combination of internal radioactive decay and flexing--perhaps concentrated within the tiger stripe fractures and brought about by the particular characteristics of Enceladus' orbit--is implicated as the source of the heat creating the liquid reservoirs. However, it is not yet clear how the deep interior of Enceladus functions, nor whether the moon is fully differentiated (separated into layers, with rock at the center and ice outside).

And, later, calthrates: ScienceDaily: Scientists Propose Alternate Model For Plume On Saturn's Moon Enceladus (http://www.sciencedaily.com/releases/2006/12/061215091052.htm)


Kieffer and colleagues have proposed an alternate model to explain the plume on Enceladus. The gases in the plume, they propose, are dissolved in a reservoir of clathrate under the water ice cap in the south polar region. The clathrate model allows an environment that would be 80 to 100 degrees Celsius colder than liquid water, with a "Frigid Faithful" plume emanating from clathrates, rather than from liquid water reservoirs.

Ignoramus
2007-Mar-18, 09:14 PM
"The team concludes that so far, all the findings and the hot start model indicate that a warm, organic-rich mixture was produced below the surface of Enceladus and might still be present today, making the moon a promising kitchen for the cooking of primordial soup"
When one then realizes that the "Kitchen" must be localized under the Southern Polar Region of Enceladus, because only there does the "smoke " appear, the "explanation" itself looks like smoke.

magman
2007-Mar-19, 12:08 PM
Tsk tsk tsk

Bad astronomy, very bad astronomy :(

John Mendenhall
2007-Mar-19, 03:24 PM
Tsk tsk tsk

Bad astronomy, very bad astronomy :(

No, no, when you're going "What is that?!", it's good astronomy. And the first guesses about what it is may be wrong.

Also, talk about difficult to figure out, what happens with radioactive heating is very hard to analyze. It depends on how much radioactive material the object started out with, where it is, and there's always the possibility of more arriving with impactors. Even for the Earth, it's a lot of guesswork, and we live here. What's it like for Jupiter, where we can't even see the surface, much less the interior?

magman
2007-Mar-19, 11:30 PM
So what other mechanisims might be at play here then?

Jerry
2007-Mar-20, 07:03 PM
I would have thought that gravitational action was causing the moon to spew out water.
I wonder if that hypothesis was considered.

Yes - the main problem is Mira (?), a sister moon of Enceladus - why would one moon squeeze enough to pop water out of the bottom, but not the other...and why at the bottom, when the gravitational effects are strongest at the equator?

This 'hot start' mechanism doesn't explain why Enceladus would be hotter in the first place, so it has the same 'flaw'. There is also the problem with ammonia - it just doesn't seem to be escaping like water and other gases.

01101001
2007-Mar-22, 08:44 PM
Yes - the main problem is Mira (?), a sister moon of Enceladus - why would one moon squeeze enough to pop water out of the bottom, but not the other...and why at the bottom, when the gravitational effects are strongest at the equator?

A problem with polar geysers? Did you hear something that ruled out the tilting? Is the data in on the craters and gravity field? I thought the tilting model was still viable.

NASA mission news: NASA-Funded Study Says Saturn's Moon Enceladus Rolled Over
(http://www.nasa.gov/mission_pages/cassini/media/cassini-20060531.html)


"The mystery we set out to explain was how the hot spot could end up at the pole if it didn't start there," said Francis Nimmo, assistant professor of Earth sciences, University of California, Santa Cruz.

NewScientist: Did Saturn's volcanic moon roll with it? (http://space.newscientist.com/channel/solar-system/cassini-huygens/dn9248-did-saturns-volcanic-moon-roll-with-it.html)


Saturn's tiny moon Enceladus may have tilted over, stabilising itself as warm ice or rock welled up from beneath its surface, a new study suggests. The analysis may explain why there is a "hotspot" that spews water vapour and ice situated exactly on its south pole, while there is nothing comparable on its north pole.
The researchers say their tilting theory could be tested by observations of the moon's craters and gravity field by the Cassini probe.

By the way, I think you shouldn't expect all gravitational effects being strongest at the equator:


Researchers expect polar regions to be tidally heated more than equatorial regions, says Francis Nimmo of the University of California in Santa Cruz

As for the "sister moon" do you mean Mimas?

Tidal Heating in Enceladus (http://swiss.csail.mit.edu/users/wisdom/enceladus.pdf) (PDF)


Any mechanism for supplying the required energy must pass the “Mimas test” (Squyres
et al. 1983). Mimas has an ancient surface, but is closer to Saturn than Enceladus and has
a larger orbital eccentricity. Any mechanism that is proposed to heat Enceladus must not
substantially heat Mimas. Using the conventional tidal heating formula (Peale and Cassen
1978; Peale 2003), the estimated tidal heating in Mimas is about 30 times the heating in
Enceladus, if the rigidity of the two bodies is the same. Thus conventional tidal heating in
the current orbital configuration does not pass the test.
One mechanism for heating Enceladus that passes the Mimas test is the secondary
spin-orbit libration model (Wisdom 2004).

also (and regarding another potential "sister moon")...


Lissauer et al. (1984) suggested that Enceladus might have recently been involved in a 2:1
mean motion resonance with Janus.

and...


There are other possibilities for resonance configurations involving Enceladus in the past
(see fig. 1). Perhaps tidal heating in these resonances was responsible for past resurfacing
events. These resonances include the 3:2 Mimas-Enceladus and the 3:4 Enceladus-Tethys
resonances.

And further mechanisms are hypothesized. The problem doesn't seem so much coming up with an explanation, but in deciding which one(s) are right.

John Mendenhall
2007-Mar-26, 05:31 PM
And further mechanisms are hypothesized. The problem doesn't seem so much coming up with an explanation, but in deciding which one(s) are right.

I got it, I got it!

It's not geysers on Enceladus, it's ion thrusters. That's why they're only at the south pole. The little green men are taking the entire moon to Alpha Centauri!

Jerry
2007-Mar-27, 07:20 PM
And further mechanisms are hypothesized. The problem doesn't seem so much coming up with an explanation, but in deciding which one(s) are right.aye mate, that would be the rub

...So provisionally lining-out mechanisms that should cause similar effects in Mimas seems a reasonable place to start. I'm not too hot on the 'rolling solution' - why would it roll?

There are a lot of new things about the Saturn system that defy simple explanation...maybe we have already lined-out too many options.

Nick4
2007-Jun-07, 04:58 AM
I dont think we will be sending people to this moon any time soon