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Stardust Analysis Results, initial results for comet Wild 2, including organic compounds
Guest_AlexBlackwell_*
post Mar 13 2006, 10:11 PM
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March 13, 2006

RELEASE: 06-091

NASA's Stardust Findings May Alter View of Comet Formation

Samples from comet Wild 2 have surprised scientists, indicating the
formation of at least some comets may have included materials ejected by
the early sun to the far reaches of the solar system.

Scientists have found minerals formed near the sun or other stars in the
samples returned to Earth by NASA's Stardust spacecraft in January. The
findings suggest materials from the center of the solar system could
have traveled to the outer reaches where comets formed. This may alter
the way scientists view the formation and composition of comets.

"The interesting thing is we are finding these high-temperature minerals
in materials from the coldest place in the solar system," said Donald
Brownlee, Stardust principal investigator from the University of
Washington, Seattle.

Scientists have long thought of comets as cold, billowing clouds of ice,
dust and gases formed on the edges of the solar system. But comets may
not be so simple or similar. They may prove to be diverse bodies with
complex histories. Comet Wild 2 seems to have had a more complex history
than thought.

"We have found very high-temperature minerals, which supports a
particular model where strong bipolar jets coming out of the early sun
propelled material formed near to the sun outward to the outer reaches
of the solar system," said Michael Zolensky, Stardust curator and
co-investigator at NASA's Johnson Space Center, Houston. "It seems that
comets are not composed entirely of volatile rich materials but rather
are a mixture of materials formed at all temperature ranges, at places
very near the early sun and at places very remote from it."

One mineral found in the material brought back by Stardust is olivine, a
primary component of the green sand found on some Hawaiian beaches. It
is among the most common minerals in the universe, but scientists were
surprised to find it in cometary dust.

Olivine is a compound of iron, magnesium and other elements. The
Stardust sample is primarily magnesium. Along with olivine, the dust
from Wild 2 contains high-temperature minerals rich in calcium, aluminum
and titanium.

Stardust passed within 149 miles of comet Wild 2 in January 2004,
trapping particles from the comet in an exposed gel. Its return capsule
parachuted to the Utah desert on Jan. 15. The science canister with the
Wild 2 sample arrived at Johnson on Jan. 17. Samples have been
distributed to approximately 150 scientists for study.

"The collection of cometary particles is greater than we ever expected,"
said Stardust Deputy Principal Investigator Peter Tsou of NASA's Jet
Propulsion Laboratory, Pasadena, Calif. "The collection includes about
two dozen large tracks visible to the unaided eye."

The grains are tiny, most smaller than a hair's width. Thousands of them
appear to be embedded in the glass-like aerogel. A single grain of 10
microns, only one-hundredth of a millimeter (.0004 inches), can be
sliced into hundreds of samples for scientists.

In addition to cometary particles, Stardust gathered interstellar dust
samples during its seven-year journey. The team at Johnson's curatorial
facility hopes to begin detailed scanning of the interstellar tray
within a month. They will initiate the Stardust at Home project. It will
enable volunteers from the public to help scientists locate particles.

After registering, Stardust at Home participants may download a virtual
microscope. The microscope will connect to a server and download "focus
movies." The movies are images of the Stardust Interstellar Dust
Collector from an automated microscope at the Cosmic Dust Lab at
Johnson. Participants will search each field for interstellar dust impacts.

NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Stardust
mission for NASA's Science Mission Directorate, Washington. Lockheed
Martin Space Systems, Denver, developed and operated the spacecraft.

Stardust science team members presented their first findings this week
at the annual Lunar and Planetary Science Conference in League City, Texas.

For more information about Stardust on the Web, visit:

http://www.nasa.gov/stardust

For information about NASA and agency programs on the Web, visit:

http://www.nasa.gov/home

- end -
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Guest_AlexBlackwell_*
post Mar 13 2006, 10:25 PM
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Emily just posted a new entry on this in her blog.
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Guest_BruceMoomaw_*
post Mar 14 2006, 01:45 AM
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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.
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Guest_AlexBlackwell_*
post Mar 14 2006, 02:03 AM
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QUOTE (BruceMoomaw @ Mar 14 2006, 01:45 AM) *
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.
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nprev
post Mar 14 2006, 03:20 AM
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QUOTE (AlexBlackwell @ Mar 13 2006, 06:03 PM) *
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?


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Guest_BruceMoomaw_*
post Mar 14 2006, 03:56 AM
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It would be more accurate to say that low temperatures are already known to slow the reaction of olivine and water WAY down, even when you're talking about cold liquid water -- a fact which a growing number of abstracts are citing to suggest that the presence of olivine scattered across Mars isn't really all that strong as evidence of a frozen surface in the Noachian era (especially since it also now looks as though most of the olivine that's been detected there was thrown up volcanically onto the surface during the Hesperian era, AFTER Mars had lost its initial dense atmosphere and that atmosphere's greenhouse effect). The same thing, of course, applies to comets -- whose total fraction of their water supply that's ever been melted into liquid form, even briefly, is probably much smaller than Mars' percentage.
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dvandorn
post Mar 14 2006, 10:00 AM
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In re this first press conference...

First, why no mention of the organic materials we've been hearing rumors about? A lot of discussion of minerals, but it took a reporter's question about organics for them to discuss it at all. And when they did, all they discussed was how difficult it is to differentiate between real organics in the samples and contamination from the lab. Are we to take it that we won't get *any* discussion of possible organics in the samples, because they're too gun-shy to ascribe organics to the samples themselves?

Second, these guys seem really blown away by seeing high-temperature-differentiated minerals (olivines, pyroxines, anorthosites, etc.) in a body that accreted in the outer solar system. Anyone ever mention the T-Tauri winds to these guys? It's been known for a long time that the Sun blew all of the loose material from the solar nebula out into a shell at *least* as far out as the Kuiper belt during its T-Tauri stage. So why does it surprise anyone that we find grains of high-temperature minerals in bodies that accreted in the Kuiper belt? After all, those bodies had to have vacuumed up a lot of the dust and gasses pushed out from the inner system during the T-Tauri epoch, right?

I guess it's just surprising to me how amazed these guys get when their results support decades-old theories...

On the plus side, I heard one of the panel members state that Stardust@Home ought to get going in the next couple of weeks. I'm looking forward to hearing from them.

-the other Doug


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edstrick
post Mar 14 2006, 10:44 AM
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I think one reason they're giving a lot of attention to the high-temp crystals and stuff is that they're the "easy pickings"... large grains that penetrate well into the aerogel and make nice dots at the end of tracks. Unaltered outer solar system dust-bunny sub-sub-micrometer grain aggregates are gonna be a lot harder to get and process, even if it's most of the total sample returned. Only micrometer'ish sized solitary grain clusters of hydration rich or organics rich outer-nebula stuff is going to be unaltered.
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Guest_RGClark_*
post Mar 14 2006, 11:46 AM
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QUOTE (BruceMoomaw @ Mar 14 2006, 03:56 AM) *
It would be more accurate to say that low temperatures are already known to slow the reaction of olivine and water WAY down, even when you're talking about cold liquid water -- a fact which a growing number of abstracts are citing to suggest that the presence of olivine scattered across Mars isn't really all that strong as evidence of a frozen surface in the Noachian era (especially since it also now looks as though most of the olivine that's been detected there was thrown up volcanically onto the surface during the Hesperian era, AFTER Mars had lost its initial dense atmosphere and that atmosphere's greenhouse effect). The same thing, of course, applies to comets -- whose total fraction of their water supply that's ever been melted into liquid form, even briefly, is probably much smaller than Mars' percentage.


The only theory offered for the formation of the high temperature olivine is that it formed close to the Sun or another star.
HOWEVER, the theory of radiogenic heating in comets early in the Solar Systems history could also explain this.
This theory is controversial ONLY because it would raise the possibility of life on comets. Note though that radiogenic heating is a leading theory for the origin of the heating in the icy, comet-like world of Enceladus (they both have water jets.)
Note as well the theory the olivine formed close to the Sun or a star would not explain why Kuiper belt object Quaoar apparently still has internal heating, whereas radiogenic heating WOULD explain it:

Chilly Quaoar had a warmer past
Mark Peplow
Crystalline ice suggests remote object has radioactive interior.
Published online: 8 December 2004.
http://www.nature.com/news/2004/041206/pf/041206-7_pf.html


Bob Clark
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Guest_BruceMoomaw_*
post Mar 14 2006, 12:00 PM
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Bear in mind that they are only talking about such heat being adequate to create olivine in the very biggest KBOs -- comets would be MUCH too small for it. However, this is really separate from the possibility that smaller objects like comets did undergo SOME significant degree of Al-26 internal heating early on.
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edstrick
post Mar 14 2006, 12:40 PM
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RG Clark: "....This theory is controversial ONLY because it would raise the possibility of life on comets. ..."

Bull.

It's controversial because there is no indication from interplanetary dust studies, founded by Brownlee, and comet studies, that small cometary bodies ever heated up enough to produce meltwater, much less silicate melt. Evidence continues to accumulate that comets are underdense bodies ice that never melted and dusts that never turned to "mud", unlike what we think are middle and outer belt asteroid materials like the serpentinized carbonaceous chondrites and things like the Tagash Lake meteorite.

This is not to say that giant KBO's didn't heat, differentiate, melt ice and even melt silicates briefly. They probably did. But a near-Pluto sized KBO is a vastly larger object with vastly more mass per unit surface area than a few km to few tens of km comet nucleus.

Comets are probably dominated by the smaller KB objects, with some small fraction being collisional fragments from larger ones, and some being objects from the outer belt or from near Jupiter's orbit, but they will be a small fraction of the total.

Note that the presumed parent body of the Kreutz sungrazer comet family, which has been suspected of originally being perhaps 100 km or more across, (I don't have the number at hand), broke up into totally fragile crumbly chunks that disintegrate in space with little provocation like other comets have done. That one probably never melted, at least the pieces of it we see. Maybe there's a core somewhere along the sungrazers' orbit we haven't seen in human history.
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Guest_RGClark_*
post Mar 14 2006, 02:11 PM
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QUOTE (edstrick @ Mar 14 2006, 12:40 PM) *
RG Clark: "....This theory is controversial ONLY because it would raise the possibility of life on comets. ..."

Bull.

It's controversial because there is no indication from interplanetary dust studies, founded by Brownlee, and comet studies, that small cometary bodies ever heated up enough to produce meltwater, much less silicate melt. Evidence continues to accumulate that comets are underdense bodies ice that never melted and dusts that never turned to "mud", unlike what we think are middle and outer belt asteroid materials like the serpentinized carbonaceous chondrites and things like the Tagash Lake meteorite.
...



???

Clays have been found both in micrometeorites and carbonaceous chondrites:

CHARACTERISTICS OF PHYLLOSILICATES IN MICROMETEORITES DERIVED FROM SYNCHROTRON X-RAY DIFFRACTION ANALYSIS.
67th Annual Meteoritical Society Meeting (2004) 5074.pdf
http://www.lpi.usra.edu/meetings/metsoc2004/pdf/5074.pdf

STRUCTURE AND BONDING OF CARBON IN CLAYS FROM CI CARBONACEOUS CHONDRITES.
Laurence A.J. Garvie1 and Peter R. Buseck1,2, 1Department of Geological Sciences, Arizona State University,
Tempe, Arizona 85287-1404, ****@asu.edu, 2Department of Chemistry and Biochemistry, Arizona State
University, Tempe, Arizona, 85287
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1515.pdf

ASTEROIDAL WATER: THE EVIDENCE FROM THE AQUEOUS ALTERATION EXHIBITED BY CHONDRITIC METEORITES.
M.E. Zolensky, SN2, NASA Johnson Space Center, Houston, TX 77058 USA
Eleventh Annual V. M. Goldschmidt Conference (2001)
http://www.lpi.usra.edu/meetings/gold2001/pdf/3052.pdf

THE PETROLOGY OF FINE-GRAINED MICROMETEORITES: EVIDENCE FOR THE DIVERSITY OF PRIMITIVE ASTEROIDS.
M. J. Genge1, J. Bradley2, C. Engrand3, M. Gounelle1, R. P. Harvey4and M. M.Grady1, 1Department of Mineralogy, The Natural History Museum, London SW7 5BD,2MVA Inc, Atlanta, USA,3C. S. N. S. M., Orsay, France, 4Case Western Reserve Univ., Ohio, USA
Lunar and Planetary Science XXXII (2001)
http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1546.pdf

Mineralogy of Phyllosilicate-rich Micrometeorites and Comparison with Tagish Lake CI and Sayama CM Chondrite.
Noguchi, T.; Nakamura, T.
32nd Annual Lunar and Planetary Science Conference, March 12-16, 2001, Houston, Texas, abstract no.1541
http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1541.pdf

Phyllosilicate is another word for clay.

Note also that the theory of radiogenic heating in comets was proposed because such radioactive isotopes were *detected* in carbonaceous meteorites. From this it was deduced there would be enough early in the solar systems history to heat the interior of comets above the melting point of water.
The ONLY reason this theory remains controversial is because it would raise the possibility of life in comets.


Bob Clark
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The Messenger
post Mar 14 2006, 02:52 PM
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QUOTE (dvandorn @ Mar 14 2006, 03:00 AM) *
In re this first press conference...

First, why no mention of the organic materials we've been hearing rumors about? A lot of discussion of minerals, but it took a reporter's question about organics for them to discuss it at all. And when they did, all they discussed was how difficult it is to differentiate between real organics in the samples and contamination from the lab. Are we to take it that we won't get *any* discussion of possible organics in the samples, because they're too gun-shy to ascribe organics to the samples themselves?

Second, these guys seem really blown away by seeing high-temperature-differentiated minerals (olivines, pyroxines, anorthosites, etc.) in a body that accreted in the outer solar system. Anyone ever mention the T-Tauri winds to these guys? It's been known for a long time that the Sun blew all of the loose material from the solar nebula out into a shell at *least* as far out as the Kuiper belt during its T-Tauri stage. So why does it surprise anyone that we find grains of high-temperature minerals in bodies that accreted in the Kuiper belt? After all, those bodies had to have vacuumed up a lot of the dust and gasses pushed out from the inner system during the T-Tauri epoch, right?

I guess it's just surprising to me how amazed these guys get when their results support decades-old theories...

On the plus side, I heard one of the panel members state that Stardust@Home ought to get going in the next couple of weeks. I'm looking forward to hearing from them.

-the other Doug

This is a great debate!

I don't see how the sun could be the source of olivine - doesn't it decompose at much lower temperatures? I also wonder why it is that everything that bops into the inner solar system is always assumed to have the same primal origins as everything else. Isn't it reasonable to assume that since the sun is at least a second generation star, the composition of the solar mass could contain inhomogenious elements from more than one star and a with a variety of formation histories? For example, Phoebe appears to have a different history from any of the other Saturn moons - did it come from the asteroid belt, or interstellar space?
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Guest_AlexBlackwell_*
post Mar 14 2006, 05:20 PM
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Emily has another LPSC update.
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Guest_AlexBlackwell_*
post Mar 14 2006, 06:16 PM
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QUOTE (dvandorn @ Mar 14 2006, 10:00 AM) *
Second, these guys seem really blown away by seeing high-temperature-differentiated minerals (olivines, pyroxines, anorthosites, etc.) in a body that accreted in the outer solar system. Anyone ever mention the T-Tauri winds to these guys? It's been known for a long time that the Sun blew all of the loose material from the solar nebula out into a shell at *least* as far out as the Kuiper belt during its T-Tauri stage. So why does it surprise anyone that we find grains of high-temperature minerals in bodies that accreted in the Kuiper belt? After all, those bodies had to have vacuumed up a lot of the dust and gasses pushed out from the inner system during the T-Tauri epoch, right?

I guess it's just surprising to me how amazed these guys get when their results support decades-old theories...

As Emily notes, and which I never really doubted, the Stardust team is certainly aware of the X-wind model by Shu et al., notwithstanding their "surprise" at the refractories in the Stardust samples. Here are a few X-wind references (just bare URLs) off the top of my head:

http://www.sciencemag.org/cgi/reprint/271/5255/1545.pdf
http://www.space.com/scienceastronomy/sola...tes_010305.html
http://www.lpi.usra.edu/meetings/ess2005/pdf/9024.pdf
http://www.lpi.usra.edu/meetings/lpsc2002/pdf/1471.pdf
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