[meteorite-list] Dust in the wind

[ensoramanda at ntlworld.com]

Hi Darren, All,

and here is where the detail is...sorry about the long link...never have figured out how to make those short links!!

http://docs.google.com/gview?a=v&q=cache:UCwD2iKBCesJ:www.dtm.ciw.edu/users/nittler/preprints/Busemann2009EPSL.pdf+*Busemann,+H.,+et+al.,+Ultra-primitive+interplanetary+dust+particles+from+the+comet+26P/Grigg%E2%80%93Skjellerup+dust+stream+collection,+Earth+Planet.+Sci.+Lett.+(2009),+doi:10.1016/j.epsl.2009.09.007&hl=en&gl=uk&pid=bl&srcid=ADGEESgM5kH7cXN7mr3Fi2-a0t_e6k4x_4CtwCzFw95JP96axFpuafqTzeMji9qnO9121azGdv-IPp2M6dxaXlZunUbm8f0oftwb1g_skGOPr2omUnnPrkic7ewhIXjgbfCizPQUpWxH&sig=AFQjCNEIVrqaqzoT7PnhncC1OXm4Y_o3fQ

Graham, UK


---- Darren Garrison <cynapse at charter.net> wrote: 

> http://www.eurekalert.org/pub_releases/2009-11/ci-pf110209.php

> 

> 'Ultra-primitive' particles found in comet dust

> 

> Washington, D.C.—Dust samples collected by high-flying aircraft in the upper

> atmosphere have yielded an unexpectedly rich trove of relicts from the ancient

> cosmos, report scientists from the Carnegie Institution. The stratospheric dust

> includes minute grains that likely formed inside stars that lived and died long

> before the birth of our sun, as well as material from molecular clouds in

> interstellar space. This "ultra-primitive" material likely wafted into the

> atmosphere after the Earth passed through the trail of an Earth-crossing comet

> in 2003, giving scientists a rare opportunity to study cometary dust in the

> laboratory.

> 

> At high altitudes, most dust in the atmosphere comes from space, rather than the

> Earth's surface. Thousands of tons of interplanetary dust particles (IDPs) enter

> the atmosphere each year. "We've known that many IDPs come from comets, but

> we've never been able to definitively tie a single IDP to a particular comet,"

> says study coauthor Larry Nittler, of Carnegie's Department of Terrestrial

> Magnetism. "The only known cometary samples we've studied in the laboratory are

> those that were returned from comet 81P/Wild 2 by the Stardust mission." The

> Stardust mission used a NASA-launched spacecraft to collect samples of comet

> dust, returning to Earth in 2006.

> 

> Comets are thought to be repositories of primitive, unaltered matter left over

> from the formation of the solar system. Material held for eons in cometary ice

> has largely escaped the heating and chemical processing that has affected other

> bodies, such as the planets. However, the Wild 2 dust returned by the Stardust

> mission included more altered material than expected, indicating that not all

> cometary material is highly primitive.

> 

> The IDPs used in the current study were collected by NASA aircraft in April

> 2003, after the Earth passed through the dust trail of comet Gregg-Skjellerup.

> The research team, which included Carnegie scientists Nittler, Henner Busemann

> (now at the University of Manchester, U.K.), Ann Nguyen, George Cody, and seven

> other colleagues, analyzed a sub-sample of the dust to determine the chemical,

> isotopic and microstructural composition of its grains. The results are reported

> on-line in Earth and Planetary Science Letters.*

> 

> "What we found is that they are very different from typical IDPs" says Nittler.

> "They are more primitive, with higher abundances of material whose origin

> predates the formation of the solar system." The distinctiveness of the

> particles, plus the timing of their collection after the Earth's passing through

> the comet trail, point to their source being the Gregg-Skjellerup comet.

> 

> "This is exciting because it allows us to compare on a microscopic scale in the

> laboratory dust particles from different comets," says Nittler. "We can use them

> as tracers for different processes that occurred in the solar system

> four-and-a-half billion years ago."

> 

> The biggest surprise for the researchers was the abundance of so-called presolar

> grains in the dust sample. Presolar grains are tiny dust particles that formed

> in previous generations of stars and in supernova explosions before the

> formation of the solar system. Afterwards, they were trapped in our solar system

> as it was forming and are found today in meteorites and in IDPs. Presolar grains

> are identified by having extremely unusual isotopic compositions compared to

> anything else in the solar system. But presolar grains are generally extremely

> rare, with abundances of just a few parts per million in even the most primitive

> meteorites, and a few hundred parts per million in IDPs. "In the IDPs associated

> with comet Gregg-Skjellerup they are up to the percent level," says Nittler.

> "This is tens of times higher abundances than we see in other primitive

> materials."

> 

> Also surprising is the comparison with the samples from Wild 2 collected by the

> Stardust mission. "Our samples seem to be much more primitive, much less

> processed, than the samples from Wild 2," says Nittler, "which might indicate

> that there is a huge diversity in the degree of processing of materials in

> different comets."

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