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

[drtanuki]

Dear Jeff and list,
  Jeff, a third try.

Oxygen isotopic analysis: Z. Sharp, University of New Mexico

Oxygen isotopic analyses of three small (2-5 mg) pieces of GRA 06129 yielded the following results which fall in the Earth, Moon and enstatite meteorite field:

δ17O = 3.04, δ18O = 6.01, Δ18O = -0.09
δ17O = 2.89, δ18O = 5.63, Δ18O = -0.03
δ17O = 3.05, δ18O = 6.01, Δ18O = -0.07

[where Δ18O = δ17O - 0.52 x δ18O]

Dirk...Tokyo


--- On Sat, 1/10/09, Jeff Kuyken <info at meteorites.com.au> wrote:


> From: Jeff Kuyken <info at meteorites.com.au>

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

> To: mpg444 at yahoo.com, "Meteorite List" <meteorite-list at meteoritecentral.com>

> Date: Saturday, January 10, 2009, 11:32 PM

> 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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