[meteorite-list] Scientists Publish 1st Ever Evidence of Asteroids with Earth-like Crust
From: drtanuki <drtanuki_at_meteoritecentral.com>
Date: Sat, 10 Jan 2009 06:30:40 -0800 (PST)
Dear Mike and List,
Here is a link to photos of the Graves Nunataks GRA 06128 and GRA 06129 mentioned in the post by Mike. What fantastic meteorites!
Best Regards, Dirk Ross...Tokyo
--- On Sat, 1/10/09, Mike Groetz <mpg444 at yahoo.com> wrote:
> From: Mike Groetz <mpg444 at yahoo.com>
> Subject: [meteorite-list] Scientists Publish 1st Ever Evidence of Asteroids with Earth-like Crust
> To: "Meteorite List" <meteorite-list at meteoritecentral.com>
> Date: Saturday, January 10, 2009, 11:13 PM
> (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
> This research was funded by the NASA cosmochemistry
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Received on Sat 10 Jan 2009 09:30:40 AM PST