[meteorite-list] Giant Asteroid Fragment Makes Impact

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu May 11 13:28:22 2006
Message-ID: <200605111726.KAA11559_at_zagami.jpl.nasa.gov>

Public Relations Office
Cardiff University
Cardiff, U.K.

May 11, 2006

Giant asteroid fragment makes impact

A first-ever discovery of a fragment from a giant meteorite which
crashed to Earth millions of years ago could cause a re-think about
asteroid collisions with our planet.

Dr Iain McDonald of the School of Earth Ocean & Planetary Sciences was
among the international research team who identified the 25cm sized
fragment, found in a frozen magma pool at the bottom of the giant
Morokweng crater in South Africa. The unique discovery, which has just
been published in Nature, gives a direct insight into what was happening
in the solar system 144 million years ago.

The researchers found the fossilised meteorite fragment 766m below the
surface whilst helping a company searching for copper and nickel in the
giant Morokwong crater in South Africa. The international team comprised
researchers from South Africa, America, Canada and the Universities of
Cardiff and Glasgow.

Dr McDonald, who led the UK component of the research team, said: "This
was a huge stroke of luck, as had the borehole been sited just a metre
away, it may have missed the object altogether. For the first time it is
possible to hold in your hand an actual piece of a giant asteroid that
hit the Earth. This intact fragment may tell us a lot more about the
insides of asteroids than we currently know."

Scientists have long believed that large asteroids or comets are
obliterated by the enormous temperatures created when they collide with
the Earth. Smaller impact craters of less than 4 kilometers diameter
have been found to contain meteorite fragments. It was thought that any
asteroid generating a crater larger than 4 kilometres in diameter would
be completely destroyed, but the new discovery challenges that view.

Morokweng is a very large crater of 70 kilometres diameter, and the
fragment?s survival suggests the asteroid struck the Earth at a lower
speed than has been assumed in the past.

Dr McDonald, who analysed the composition of the fragment, revealed a
further twist to the story of the meteorite, of a type called an
ordinary chondrite.

He said: "Morokweng is no run of the mill meteorite. It shows some
striking differences when compared with other known meteorites, such as
the absence of iron-nickel metal. It appears that the Morokweng
meteorite may have come from a very different part of the parent
asteroid than other ordinary chondrites which currently fall to earth."

To highlight its unique status, fragments of the asteroid have gone on
display at the Science Museum's Antenna news gallery from Thursday 11th May.
Received on Thu 11 May 2006 01:26:16 PM PDT