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Fraser
2004-Jun-18, 06:22 PM
SUMMARY: Scientists are still digesting the volumes of data gathered by NASA's Stardust spacecraft when it buzzed past Comet Wild 2 earlier this year. They were expecting to see a dirty snowball, but found a much stranger place, with deep craters, steep cliffs, and dozens of blasting jets. Some features look ancient, perhaps created billions of years ago when life was just forming on Earth. Stardust collected particles from the comet when it flew past, and is now returning to Earth so scientists can study them in closer detail.

What do you think about this story? Post your comments below.

martyism
2004-Jun-18, 09:35 PM
Clearly the Stardust photos are an outragiously transparent fake. Proof? The right foot only has three toes and the left none (count 'em zero, nada, and zilch). What could NASA have been thinking? Even bigfoot had all his toes and fingers. Tsk, Tsk, Tsk.

Martyism
;)

Stunning and thought provoking pics! I find it amazing that we have so much to learn yet about even the simple stuff like the basic physical make up of a comet which we were so certain about for so long.

VanderL
2004-Jun-18, 09:44 PM
Stunning pictures indeed, there's one thing missing really. Where exactly are the jets emanating from?

I can't find any image or hint to where the heatsources are that makes these jets spew forth. Apart from an animation on the website (an artists' impression) there's no clear image anywhere. I imagine that sublimation is something that can be imaged. I think this is a bit mysterious, is there anything wrong here?

Cheers.

om@umr.edu
2004-Jun-19, 12:14 AM
Originally posted by VanderL@Jun 18 2004, 09:44 PM
Stunning pictures indeed, there's one thing missing really. Where exactly are the jets emanating from?

I can't find any image or hint to where the heatsources are that makes these jets spew forth.
VanderL,

I guess the jets come from highly volatile compounds being heated and turned into gas by radiation from the Sun.

The outer part of the solar system is very cold but very rich in volatile elements.

When comets bring material - frozen solid in the outer part of the solar system - close to the Sun, it would not be surprising if the solid (perhaps solid methane, for example) is converted to gas.

I hope they made isotope measurements when the Stardust spacecraft buzzed past Comet Wild 2.

I suspect heavy elements in the Comet have "strange" isotope abundances.

The Jupiter atmosphere is composed almost entirely of these highly volatile elements.

The Galileo Probe found "strange" xenon (enriched in r-products from a supernova explosion) in Jupiter.

http://www.umr.edu/~om/abstracts2001/windl...leranalysis.pdf (http://www.umr.edu/~om/abstracts2001/windleranalysis.pdf)

With kind regards,

Oliver
http://www.umr.edu/~om

antoniseb
2004-Jun-19, 01:22 AM
Originally posted by om@umr.edu@Jun 19 2004, 12:14 AM
I suspect heavy elements in the Comet have "strange" isotope abundances.
Are you saying that if the comet had terestrial isotope abundances that the jets would not be there? Or was this simply an off-topic remark?

om@umr.edu
2004-Jun-19, 01:08 PM
Originally posted by antoniseb+Jun 19 2004, 01:22 AM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (antoniseb &#064; Jun 19 2004, 01:22 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-om@umr.edu@Jun 19 2004, 12:14 AM
I suspect heavy elements in the Comet have "strange" isotope abundances.
Are you saying that if the comet had terestrial isotope abundances that the jets would not be there? [/b][/quote]
I am sorry, Anton, that my message was unclear.

In meteorite minerals (and in planets) we observe:

-1. "Strange" isotope ratios of heavy elements associated with abundant light elements.

-2. The light elements themselves may have "normal" isotope ratios.

-3. More "normal" isotope ratios of heavy elements associated with Fe, Ni, S.[/i]

For example, we observe:

-1. "Strange" Xe-2 (in Jupiter) and in diamonds extracted from carbonaceous chondrites.

-2. "Normal" carbon isotope ratios in the matrix of the diamond itself.

-3. "Normal" Xe-1 (in Earth and Mars) and in (Fe,Ni)S inclusions of meteorites.

Therefore, if the jets in the comet arise from volatilization of frozen light elements from the outer part of the solar system, then heavy elements emitted in the jet will probably have "strange" isotope ratios.

E.g., if vaporization of frozen methane produces the jets, "strange" Xe-2 will likely be released with the CH4 gas.

With kind regards,

Oliver
http://www.umr.edu/~om

antoniseb
2004-Jun-19, 01:37 PM
Your predictions seem reasonable, and will be validated or upset by the Stardust probe when it returns in a few years. Reading your reply to VanderL, I had misread what you were writing as being part of an attempt to answer his question. I see now that you were making a whole new point about the Stardust mission.

As a side note, I&#39;d suggest coming up with a different terminology to describe the isotope ratios of Xenon. Terrestrial and Jovian as opposed to Normal & Strange would make your writing more clear. Also it would leave room for other abundance ratios as they are observed [Solar, Avg CC, Martian, Venutian, Saturnian, etc].

VanderL
2004-Jun-19, 10:49 PM
Thanks Oliver for the interesting "aside", but I&#39;m still left with the original question: Where exactly are the jets emanating from? Any thoughts why there is no image clearly showing where the jets originate?



Cheers.

Victoria
2004-Jun-20, 02:09 AM
Check this...geyser... <_< volcanic :unsure: a comet with so much activity. I have to ask; what exactly is the diameter of the common comet?

om@umr.edu
2004-Jun-21, 10:18 AM
Originally posted by VanderL@Jun 19 2004, 10:49 PM
Thanks Oliver for the interesting "aside", but I&#39;m still left with the original question: Where exactly are the jets emanating from?

Sorry, VanderL.

I do not know exactly from where the are jets emanating.

However, I suspect the jets are produced by rapid vaporization of volatile material that was frozen onto the comet as it traversed the outer part of the solar system.

I have also proposed a measurement to test that suggestion.

"Strange" Xe-2 is dominant in volatile material of the outer part of the solar system. Isotope measurements can easily distinguished this from "Normal" Xe-1 that is dominant in the inner part of the solar system.

Thus, isotope measurements on xenon can test the validity of my hypothesis.

Differences between Xe-1 and Xe-2 are explained in more detail at
http://www.umr.edu/~om/abstracts2002/soho-gong2002.pdf
http://www.umr.edu/~om/abstracts2002/soho-gong2002.ps

With kind regards,

Oliver
http://www.umr.edu/~om

VanderL
2004-Jun-21, 03:49 PM
Thanks Oliver,

No doubt the results of the Stardust collector can validate your hypothesis, but normally when such clearcut answers are to be expected, the results tend to be ambiguous. Hopefully these results will give clear answers, but somehow I doubt that will happen.
My concern about the jets is that, although the jets and the comet have been imaged spectacularly, there is no mention of the source of the jets. I personally think the Sunlight isn&#39;t strong enough to to heat the comet&#39;s surface enough to generate these powerful jets, so I&#39;m curious what the images can show us. Maybe I missed those particular images, but I wonder if maybe the pictures aren&#39;t detailed enough to answer the question, or that perhaps something unexpected was found that needs time to be interpreted. In any case, I hope more information will become available soon.

Cheers.

VanderL
2004-Jun-22, 03:18 PM
There is more information:
http://antwrp.gsfc.nasa.gov/apod/

At APOD (22-06-2004) there are more detailed images of a spire on comet Wild2, and links to the surprise that comet Wild2 (just like comet Hale-Bopp) has multiple jets even far away from the Sun. This would add to my suspicion that solar heat alone is possibly not enough to produce the jets in comets.


Cheers.

Victoria
2004-Jun-22, 04:37 PM
Great link VanderL. Sweet and simple. :) Until true results are found explaining the mystery behind the comets wild activity, imaginations like mine will certainly be filled with ideas. :D

John L
2004-Jun-22, 07:08 PM
I think the reason you don&#39;t see images of the jets eminating from the comet is because of contrast. Its the same reason pictures of astronauts taken on the surface of the Moon don&#39;t have any stars in the sky. The settings on the Stardust cameras probably had to be set to pick up the comet surface, or the jets of gas, but probably couldn&#39;t do both at once...

Duane
2004-Jun-22, 07:34 PM
Hey thats what I was going to say&#33;

VanderL
2004-Jun-22, 09:27 PM
Hmm, there is an overlay where the jets are indicated, just not in detail. My guess is that when the jets are presented in 3-D, at least the area where they emanate from can be found. The next thing is figuring out what the similarities of these points are and deduce how the jets work. I doubt that the problem is in the imaging, maybe there are no geysers (or however we should call the supposed jet source) to be imaged?
I hope the Stardust scientists are just building up to release these details, maybe the gathered dust will also give some new information. But that&#39;s more than a year away. At least there are still some reasons to investigate a comet and hopefully the Rosetta lander will show us even more details (unfortunately that&#39;s an even longer wait).


Cheers.

imported_General Zod
2004-Jun-23, 03:36 AM
It would be REALLY interesting, if unlikely, if it or another comet on our hit list turns up to be foreign, a wanderer captured by our solar system. Perhaps a comet formed in the same stellar nursery as our own dear sun. Or better yet, a truly ancient comet that predates our system by a few billion years.

As for the jets, well, Im no expert and can barely speak my own language (TEXAN), but I thinka sublimation is the most likely source. I dont see gravitational stress on the interior would be a factor until it was VERY close to the sun, but perhaps as it swings by it does get "stirred up a bit" before it is flung back out into the great beyond to refreeze, and repeat the cycle. As for gathering more material in the outer solar system and the Oort cloud, I am sure it picks up a bit, but if large enough quantites were present, wouldnt we have noticed a "Haze" of material obstructing our view a tiny bit?

Perhaps comets vary more in their composition than we realize. Seems like that with so much water ice floating around out there, there would be more of it deposited on all the rocky planets, in great quantities. The moon and Mars for instance. I anticipate the return of the information gathered and the samples.

VanderL
2004-Jun-26, 10:58 PM
I constantly hear the NASA people talk about the fact that comet Wild2 is unlike anything they have seen in the solar system. But Wild2 looks an awful lot like Phoebe (not to scale of course) and also like Borrelly, Ida and Phobos to name a few. I read somewhere (can&#39;t seem to find it anymore) that some jets from Wild2 were emanating from darkside spots which would be hard to explain when the necessary heat comes from sunlight. Also the jets are described as very violent and highly collimated, which also is against what can be expected from outgassing processes.
Plus the fact that the surface is extremely accentuated (craters, pits cliffs and even spires) makes me doubt that we are looking at "dirty snowballs", where such features wouldn&#39;t last very long.


Cheers.

wjwduke
2004-Jun-26, 11:41 PM
I am a bit confused over the speculation as to where the jets are coming from. As in all bodies with mass, be they tens of kilometers or hundreds or millions of kilos in diameter, all have a pressure directed towards their center. The contents of the central core obviously vary based on the circumstances of their birth. Because we see jets eminating from Wild2, it is obvious that the core of this object has "gas" the molecular makeup at this point is not known and hopefully the returned samples will give us some insight.
Ok, as all massive bodies traveling through space are subjected to n-body gravitational influences, I would suspect that, just as here on earth, a bit of techtonics might be involved whereby topological surface stress causes vents to open and close randomly which consequently results in random jets as seen (briefly) in the fly-by. Just a thought or am I way out of line here?
Thanks for listening, wjwduke

wjwduke
2004-Jun-26, 11:44 PM
Sorry for mispelling tectonics.
wjwduke

VanderL
2004-Jun-27, 09:16 AM
Hi wjwduke,

That&#39;s basically true: gravitational "flexing" will always work no matter how small the object, but what matters here is that the effect is extremely small. And the smaller the object the smaller the heating effect. I&#39;m not completely sure how small the effect is, but I think it does not contribute to creating vents on comets. Actually, the tectonics we see here on Earth are a consequence of the fluidity of the Earth&#39;s "innards", the magma makes it possible for the rocky outer layer to "float" and move around. The internal heat source of the Earth is thought to originate from radioactive decay of potassium, uranium and thorium. For comets, that would be insufficient, the current idea is that the jets are created through heating of the comet&#39;s surface by solar radiation, which I doubt can create these powerful, collimated jets.

My guess is that the NASA scientists either don&#39;t have enough data to speculate on what causes the jets, or they have found cunfusing data they are unable to interpret (yet).


Cheers.