[meteorite-list] Giant Asteroid Fragment Makes Impact

[Ron Baalke]

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.