[meteorite-list] Rockabye chondrules, in the protoplanetary disk...

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Wed, 19 Mar 2008 15:57:09 -0500
Message-ID: <g9v2u3968alb9v53j2q6i8e5j94hi5kcra_at_4ax.com>

http://www.sciencedaily.com/releases/2008/03/080319140319.htm

Mars, Earth And Moon From 'Unique Planetary Nursery'

Science Daily (Mar. 19, 2008) ? A study of meteorites suggests that Mars, the
Earth and the Moon share a common composition from ?growing up? in a unique
planetary nursery in the inner solar system.

The finding could lead to a rethink of how the inner solar system formed.

In the journal Nature the international team of scientists, which includes
Professor Alex Halliday from Oxford University?s Department of Earth Sciences,
report how they analysed 16 meteorites that fell to Earth from Mars. They found
that the amounts of neodymium-142 these contain are subtly different from those
of objects found in the asteroid belt. This isotopic fingerprint is proof that
the chemistry of the inner solar system was different even for elements that are
hard to vapourise.

Professor Halliday said: ?The Earth, Moon and Mars appear to have formed in a
part of the inner solar system with a ratio of samarium to neodymium that is
around 5 per cent more than could be found in the asteroid belt. It is this
?family resemblance? that we see today when we compare oceanic basalts from
Earth with Moon rocks and Martian meteorites. Such differences may be the result
of the erosion of planetary crusts during formation events, alternatively, this
composition arose from the sorting of clouds of partially melted droplets or
grains - known as ?chondrules?.?

Earth has a long geological history of recycling the materials that make up its
crust and mantle, which could help explain why its composition is different from
that of other planetary bodies ? it could, for example, have deeply buried
reservoirs of certain elements. However Mars and the Moon are believed to have
been nothing like as active during their lifespan: making it much more difficult
for any theory involving material recycling to explain why their composition
should differ from other planetary bodies and yet have such similarities with
the composition of the Earth.

Professor Halliday said: ?What our results suggest is that the sorting of the
elements that make up these planets may have happened at a much earlier stage
than had been believed. It may even be that this sorting happened in the
accretion disk out of which Mars and the early Earth first formed. What we can
say is that the composition of these worlds is inconsistent with them simply
forming out of large ?lumps? of stony meteorites, like those we see today in the
asteroid belt.?

A report of the research, entitled ?Super-chondritic Sm/Nd in Mars, Earth and
the Moon?, is published in Nature on 20 March 2008. Co-author Alex Halliday is
Professor of Geochemistry at Oxford University?s Department of Earth Sciences
and Head of the MPLS Division. The international team included scientists from
the Universite Denis Diderot, France, the ETH Zurich, Switzerland and the Ecole
Normale Superieure de Lyon, France.

Adapted from materials provided by University of Oxford.
Received on Wed 19 Mar 2008 04:57:09 PM PDT


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