[meteorite-list] Scientists Publish 1st Ever Evidence of Asteroidswith Earth-like Crust

From: Jeff Kuyken <info_at_meteoritecentral.com>
Date: Sun, 11 Jan 2009 01:32:49 +1100
Message-ID: <D4670B69C75346199DB43EE37948970E_at_JeffPC>

Hey all,

Does anyone know if there are any Oxygen Isotope results available? Where do
these plot?



----- Original Message -----
From: "Mike Groetz" <mpg444 at yahoo.com>
To: "Meteorite List" <meteorite-list at meteoritecentral.com>
Sent: Sunday, January 11, 2009 1:13 AM
Subject: [meteorite-list] Scientists Publish 1st Ever Evidence of
Asteroidswith Earth-like Crust

> http://media-newswire.com/release_1083611.html
> (Media-Newswire.com) - COLLEGE PARK, Md. - Two rare meteorites found in
> Antarctica two years ago are from a previously unknown, ancient asteroid
> with an outer layer or crust similar in composition to the crust of
> Earth's continents, reports a research team primarily composed of
> geochemists from the University of Maryland.
> Published in the January 8 issue of the journal Nature, this is the first
> ever finding of material from an asteroid with a crust like Earth's. The
> discovery also represents the oldest example of rock with this composition
> ever found.
> These meteorites point "to previously unrecognized diversity" of materials
> formed early in the history of the Solar System, write authors James Day,
> Richard Ash, Jeremy Bellucci, William McDonough and Richard Walker of the
> University of Maryland; Yang Liu and Lawrence Taylor of the University of
> Tennessee and Douglas Rumble III of the Carnegie Institution for Science.
> James Day looking at a portion of the meteorite in the University of
> Maryland's isotope geochemistry lab. In the background is a mass
> spectrometer used to analyze the meteorite samples. Prof. James Day
> looking at a portion of the meteorite in the University of Maryland's
> isotope geochemistry lab. In the background is a mass spectrometer used to
> analyze the meteorite samples.
> "What is most unusual about these rocks is that they have compositions
> similar to Earth's andesite continental crust -- what the rock beneath our
> feet is made of," said first author Day, who is a research scientist in
> Maryland's department of geology. "No meteorites like this have ever been
> seen before."
> Day explained that his team focused their investigations on how such
> different Solar System bodies could have crusts with such similar
> compositions. "We show that this occurred because of limited melting of
> the asteroid, and thus illustrate that the formation of andesite crust has
> occurred in our solar system by processes other than plate tectonics,
> which is the generally accepted process that created the crust of Earth."
> The two meteorites (numbered GRA 06128 and GRA 06129) were discovered in
> the Graves Nunatak Icefield during the US Antarctic Search for Meteorites
> (ANSMET) 2006/2007 field season. Day and his colleagues immediately
> recognized that these meteorites were unusual because of elevated contents
> of a light-colored feldspar mineral called oligoclase. "Our age results
> point to these rocks being over 4.52 billion years old and that they
> formed during the birth of the Solar System. Combined with the oxygen
> isotope data, this age points to their origin from an asteroid rather than
> a planet," he said.
> There are a number of asteroids in the asteroid belt that may have
> properties like the GRA 06128 and GRA 06129 meteorites including the
> asteroid (2867) Steins, which was studied by the European Space Agency's
> Rosetta spacecraft during a flyby this past September. These so-called
> E-type asteroids reflect the Sun's light very brightly, as would be
> predicted for a body with a crust made of feldspar.
> According to Day and his colleagues, finding pieces of meteorites with
> andesite compositions is important because they not only point to a
> previously unrecognized diversity of Solar System materials, but also to a
> new mechanism to generate andesite crust. On the present-day Earth, this
> occurs dominantly through plates colliding and subduction - where one
> plate slides beneath another. Subduction forces water back into the mantle
> aiding melting and generating arc volcanoes, such as the Pacific Rim of
> Fire - in this way new crust is formed.
> "Our studies of the GRA meteorites suggest similar crust compositions may
> be formed via melting of materials in planets that are initially volatile-
> and possibly water-rich, like the Earth probably was when if first formed"
> said Day." A major uncertainty is how evolved crust formed in the early
> Solar System and these meteorites are a piece in the puzzle to
> understanding these processes."
> This research was funded by the NASA cosmochemistry program.
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Received on Sat 10 Jan 2009 09:32:49 AM PST

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