[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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