[X] My Assistant

[Guest_paulanderson_*]

I thought the analysis results, as they come in, deserved their own thread. I'm interested in how these findings relate to the "weird crystals" found and reported on in the previous Nature article.

A couple more updates, from Space.com and MSNBC:

Stardust Mission Yields Ancient Comet Dust
http://space.com/scienceastronomy/060220_s...ust_update.html

Comet Dust Sparks Scientific Intrigue
http://www.msnbc.msn.com/id/11460590

"The early results reveal that the 4.5 billion-year-old comet contains iron, sulfides, glassy materials, olivine, and what the scientists termed potentially interesting isotopic traces. They believe that these materials were also available during the formation of other objects in our solar system.

What's even more amazing is how well the first round of analysis is matching expectations. Brownlee and other Stardust scientists are holding back their first formal reports for a scientific meeting in Texas next month — but during Monday's news conference, Brownlee said the samples studied so far contain iron sulfides and glassy material such as crystalline silicates. Those ingredients are found in meteorites as well.

Later, Brownlee told MSNBC.com that there were preliminary indications of organic compounds, based on telltale infrared readings. He cautioned that the initial indications were tentative and could still be traced to contaminants.

In the weeks and months ahead, Sandford and his team will be analyzing the types of carbon found in the samples — not only to trace the organics, but also to determine whether such compounds predated the formation of the solar system."

[Guest_BruceMoomaw_*]

I have to admit that I don't understand why the discovery of olivine is considered "surprising" -- they've been detecting it in IR spectra of coma dust for a long time.

[Guest_AlexBlackwell_*]

I have to admit that I don't understand why the discovery of olivine is considered "surprising" -- they've been detecting it in IR spectra of coma dust for a long time.

True.

And the model where refractory materials could have been blown from the sun outwards to the comet-forming regions is also not new.

[nprev]

True.

And the model where refractory materials could have been blown from the sun outwards to the comet-forming regions is also not new.

Hmm. Perhaps the element of surprise here is that olivine grains survived in an inner-system comet without alteration by water? As you all certainly recall, the presence of abundant olivine on the surface of Mars has been touted as evidence that the planet has been dry for most of its history.

Maybe we don't understand something about the chemistry and "catalytic" (or circumstantial) interactions between H2O and olivine. For example, is a significant atmosphere of a given composition required for olivine to decompose as it does on Earth's surface, and therefore is this assumption altering our expectations?

[Guest_AlexBlackwell_*]

Hmm. Perhaps the element of surprise here is that olivine grains survived in an inner-system comet without alteration by water?

As Mark Peplow notes in the March 16, 2006, issue of Nature (excerpt below), it appears the refractories found in the Stardust samples were "supris[ing]" because many scientists, presumably the majority of the Stardust team too, view the X-wind model as "controversial."

===================

"The presence of CAIs was predicted by one controversial theory, however. The 'X-wind' model sees strong magnetic fields around the young Sun channelling heated material to the far reaches of the protoplanetary cloud. The Stardust results do not prove anything, but they certainly fit with the idea, says Mike Zolensky of NASA's Johnson Space Center in Houston, Texas, who is leading the mineral analyses.

"The other possible source of the minerals is another star completely. Once formed, the grains may have drifted through interstellar space for eons, before reaching our own Solar System and being incorporated into Wild 2. Zolensky says it is too early to know which theory is right. But Brownlee adds that measurements of isotopes in the grains could settle the question within months — such materials often bear a distinctive isotopic signature determined by their star of origin."

[Guest_RGClark_*]

As Mark Peplow notes in the March 16, 2006, issue of Nature (excerpt below), it appears the refractories found in the Stardust samples were "supris[ing]" because many scientists, presumably the majority of the Stardust team too, view the X-wind model as "controversial."

===================

"The presence of CAIs was predicted by one controversial theory, however. The 'X-wind' model sees strong magnetic fields around the young Sun channelling heated material to the far reaches of the protoplanetary cloud. The Stardust results do not prove anything, but they certainly fit with the idea, says Mike Zolensky of NASA's Johnson Space Center in Houston, Texas, who is leading the mineral analyses.

"The other possible source of the minerals is another star completely. Once formed, the grains may have drifted through interstellar space for eons, before reaching our own Solar System and being incorporated into Wild 2. Zolensky says it is too early to know which theory is right. But Brownlee adds that measurements of isotopes in the grains could settle the question within months — such materials often bear a distinctive isotopic signature determined by their star of origin."

Thanks for the info on the presence of the calcium-aluminum inclusions (CAIs). The isotopic ratios in such inclusions found in meteorites has been used to deduce the amount of radiogenic heating in their parent bodies and whether this would be enough to raise their interiors to the melting point of water. It would be interesting to find out what they find out about the isotopic ratios in the Stardust CAIs.
In regard to the CAIs it was found in some meteorites they had to be subjected to some episodes of remelting, perhaps in the range of 2 million years after they formed. Perhaps these heating episodes could be what also caused the crystalline olivine.
Incidentally, anyone know why the remelting episodes of the CAIs and the high heat required for the Stardust olivine minerals could not be simply due impacts?

posted May 31, 2005
Making Sense of Droplets Inside Droplets
--- The vexing presence of chondrules inside supposedly older calcium-aluminum-rich inclusions (CAIs) in chondrites makes sense if the CAIs were remelted.
http://www.psrd.hawaii.edu/May05/chondrulesCAIs.html

posted September 30, 2002
Using Aluminum-26 as a Clock for Early Solar System Events
--- Correspondence between 26Al and Pb-Pb ages shows that 26Al records a detailed record of events in the early solar system.
http://www.psrd.hawaii.edu/Sept02/Al26clock.html

In looking up images of CAIs and chondrules in meteorites I came across this:


"Image of chondrules projecting from the
surface of a chondrite. Chondrules make
up the greater portion of some chondrites."
http://web.pdx.edu/~ruzickaa/G410/Hewins/glos7.html

I was struck by the similarity to the spherules of Meridiani. They also are of the same size range, a few millimeters across. However, I wasn't able to find references that suggest they contain hematite.



- Bob Clark