[meteorite-list] Dating the moon-forming impact event with meteorites

From: Shawn Alan <shawnalan_at_meteoritecentral.com>
Date: Thu, 23 Apr 2015 09:03:13 -0700
Message-ID: <20150423090313.e8713c95af9984a493c5db01816d4c10.3e260a7253.wbe_at_email22.secureserver.net>

Hello Listers


PS I have this issue on PDF

Shawn Alan
IMCA 1633
ebay store http://www.ebay.com/sch/imca1633ny/m.html
Website http://meteoritefalls.com

Dating the moon-forming impact event with meteorites
 by Staff Writers
 Tucson AZ (SPX) Apr 22, 2015

"Through a combination of data analysis and numerical modeling work,
researchers have found a record of the ancient Moon-forming giant impact
observable in stony meteorites. Their work will appear in the April 2015
issue of the Journal Science.

The work was done by NASA Solar System Exploration Research Virtual
Institute (SSERVI) researchers led by Principal Investigator Bill Bottke
of the Institute for the Science of Exploration Targets (ISET) team at
the Southwest Research Institute and included Tim Swindle, director of
the University of Arizona's Lunar and Planetary Laboratory.

The inner Solar System's biggest known collision was the Moon-forming
giant impact between a large protoplanet and the proto-Earth. The timing
of this giant impact, however, is uncertain, with the ages of the most
ancient lunar samples returned by the Apollo astronauts still being

Numerical simulations of the giant impact indicate this event not only
created a disk of debris near Earth that formed the Moon, but it also
ejected huge amounts of debris completely out of the Earth-Moon system.

The fate of this material, comprising as much as several percent of an
Earth mass, has not been closely examined until recently. However, it is
likely some of it blasted main belt asteroids, with a record plausibly
left behind in their near-surface rocks. Collisions on these asteroids
in more recent times delivered these shocked remnants to Earth, which
scientists have now used to date the age of the Moon.

The research indicates numerous kilometer-sized fragments from the giant
impact struck main belt asteroids at much higher velocities than typical
main belt collisions, heating the surface and leaving behind a permanent
record of the impact event.

Evidence that the giant impact produced a large number of
kilometer-sized fragments can be inferred from laboratory and numerical
impact experiments, the ancient lunar impact record itself, and the
numbers and sizes of fragments produced by major main belt asteroid

Once the team concluded that pieces of the Moon-forming impact hit main
belt asteroids and left a record of shock heating events in some
meteorites, they set out to deduce both the timing and the relative
magnitude of the bombardment.

By modeling the evolution of giant impact debris over time and fitting
the results to ancient impact heat signatures in stony meteorites, the
team was able to infer the Moon formed about 4.47 billion years ago, in
agreement with many previous estimates. The most ancient Solar System
materials found in meteorites are about one hundred million years older
than this age."

Received on Thu 23 Apr 2015 12:03:13 PM PDT

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