[meteorite-list] Half-baked Asteroids Have Earth-like Crust

From: Jerry Flaherty <grf2_at_meteoritecentral.com>
Date: Thu, 08 Jan 2009 21:36:05 -0500
Message-ID: <7E19E84F916841A0951CBDAA9569ACE8_at_ASUS>

WOW Andesite is a complex vocanic "paste" associated with seafloor sediment
and H2O responsible for catastrophic explosive activity in earth's geology.
It's wild to find it on astroids. They've got to be "humugous"!!!!!!!!
----- Original Message -----
From: "Ron Baalke" <baalke at zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Thursday, January 08, 2009 3:55 PM
Subject: [meteorite-list] Half-baked Asteroids Have Earth-like Crust


>
> http://esciencenews.com/articles/2009/01/07/half.baked.asteroids.have.earth.crust
>
> Half-baked asteroids have Earth-like crust
> e! Science News
> January 7, 2009
>
> [Image]
> Field image of the achondrite meteorite GRA 06129, found in blue ice of
> the Graves Nunatak region of the Antarctica during the ANSMET 2006/2007
> field-season. GRA 06129 and its pair, GRA 06128, are achondrite
> meteorites with compositions unlike any previously discovered Solar
> System materials.
> <http://esciencenews.com/files/images/20090107978550.jpg>
> Image courtesy of the Antarctic Search for Meteorites (PI - Ralph
> Harvey, Case Western Reserve University)
>
> Asteroids are hunks of rock that orbit in the outer reaches of space,
> and scientists have generally assumed that their small size limited the
> types of rock that could form in their crusts. But two newly discovered
> meteorites may rewrite the book on how some asteroids form and evolve.
> Researchers from the Carnegie Institution, the University of Maryland,
> and the University of Tennessee report in the January 8th edition of
> Nature that these meteorites are ancient asteroid fragments consisting
> of feldspar-rich rock called andesite. Similar rocks were previously
> known only from Earth, making these samples the first of their kind from
> elsewhere in the Solar System. The two meteorites were discovered during
> the Antarctic Search for Meteorites (ANSMET) 2006/2007 field season in a
> region of the Antarctic ice known as the Graves Nunatak icefield. The
> light-colored meteorites, designated GRA 06128 and GRA 06129, were
> immediately recognized as being different from previously known
> meteorites.
>
> "What is most unusual about these rocks is that they have compositions
> similar to Earth's andesite continental crust - what makes up the ground
> beneath our feet," says University of Maryland's James Day, lead author
> of the study. "No meteorites like this have ever been seen before."
>
> Andesite is an igneous rock common on Earth in areas where colliding
> tectonic plates generate volcanoes, such as those of the Andes mountain
> range. The meteorites contain minerals thought to require large-scale
> processes such as plate tectonics to concentrate the right chemical
> ingredients. In view of this, some researchers had suggested that the
> meteorites were fragments of a planet or the Moon, not an asteroid. But
> analysis of the meteorites' oxygen isotopes at the Carnegie
> Institution's Geophysical Laboratory by Douglas Rumble ruled out that
> possibility.
>
> "A number of solar system objects including parent bodies of meteorites,
> planets, moons, and asteroids have their own oxygen isotope signatures,"
> says Rumble. "Just by analyzing 16O-17O-18O ratios we can tell if a
> meteorite came from Mars, from the Moon, or from a particular asteroid.
> One extensively studied parent is the asteroid 4 Vesta. In the majority
> of cases the actual location of the parent body is unknown, but a
> particular group of meteorites may be assigned to the same parent body
> based on the isotope ratios even if the specific location of the body
> isn't known. When the ratios in meteorites are plotted against one
> another the result is mutually parallel lines offset from one another.
> The GRA 06128 and GRA 06129 meteorites, and some similar ones called
> brachinites, plot below Earth-Moon rocks and are nearly coincident with
> meteorites from 4 Vesta."
>
> The meteorites' age, more than 4.5 billion years, suggests that they
> formed very soon after the birth of the solar system. This makes it
> unlikely that they came from the crust of a differentiated planet. The
> chemical signature of some rare precious metals, notably osmium, in the
> meteorites also points to their origin on an asteroid that was not fully
> differentiated.
>
> The researchers hypothesize that that the asteroid had a diameter
> somewhat larger than 100 kilometers, which would be sufficient to hold
> enough heat for the asteroid's rocks to partially, but not completely,
> melt. The asteroid would remain undifferentiated, but the melted
> portions could erupt on the asteroid's surface to form the andesitic
> crust.
>
> "Our work illustrates that the formation of planet-like andesite crust
> has occurred by processes other than plate tectonics on solar system
> bodies," says Day. "Ultimately this may shed light on how evolved crust
> forms on planets, including Earth, during the earliest stages of their
> birth."
>
> Source: Carnegie Institution <http://www.ciw.edu>
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Received on Thu 08 Jan 2009 09:36:05 PM PST