[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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