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

[Jeff Kuyken]

Hey all,

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

Cheers,

Jeff


----- 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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