http://six.pairlist.net/pipermail/meteorite-list/2008-September/046662.html
http://cordis.europa.eu/fetch?CALLER=EN_NEWS&ACTION=D&SESSION=&RCN=29890
Meteorites could be source of world's precious metals, study finds
Rare and precious metals such as platinum, gold and iridium could have been
brought to Earth by iron meteorites, according to new research by Dr Gerhard
Schmidt of the University of Mainz in Germany.
Dr Mainz is due to present his results at the European Planetary Science
Congress (EPSC), which is taking place in Münster, Germany, from 21 to 26
September.
Gold, platinum, iridium, palladium and rhodium are examples of Highly
Siderophile Elements (HSEs), metals that tend to bond with solid or molten
metallic iron. When the Earth was still forming, it heated up, and the HSEs and
other heavy elements were stripped from the surface of the young planet into its
iron- and nickel-rich core.
This raises the question of where the HSEs found in the crust came from. One
theory is that meteorite impacts delivered these elements to the earth's surface
after the core had formed.
Over the course of 12 years, Dr Schmidt and his colleagues analysed HSE
concentrations at a number of meteorite impact sites and in the earth's crust
and mantle at other sites. They also studied samples from the surfaces of the
moon as well as Martian meteorites.
'A key issue for understanding the origin of planets is the knowledge of the
abundances of HSE in the crust and mantle of the Earth, Mars and Moon,'
explained Dr Schmidt. 'We have found remarkably uniform abundance distributions
of HSE in our samples of the Earth's upper crust. A comparison of these HSE
values with meteorites strongly suggests that they have a cosmochemical source.'
Dr Schmidt's analyses revealed that the HSE levels found in the earth's crust
are much higher than those found in stony meteorites called chondrites, which
were formed form the material present in the early solar system.
However, the HSE ratios found are very close to those found in iron or
stony-iron meteorites. These larger asteroids generated enough internal heat to
form a molten metal core. Dr Schmidt has calculated that around 160 metallic
asteroids of approximately 20 km in diameter would be enough to provide the
levels of HSEs found in the earth's crust today. Furthermore, it seems that a
similar process could have been taking place on Mars.
'The first meteorite to be found on Mars was an iron meteorite, discovered by
the Opportunity rover in January 2005,' commented Dr Schmidt. 'Analysis of the
Nahkla, Shergotty and Zagami Martian meteorites strongly supports a genetic link
with certain iron meteorites.'
The EPSC is organised by the EU-funded Europlanet initiative, which aims to
foster cooperation in European planetary science research, enhance Europe's
competitiveness in the field, promote European participation in major planetary
exploration missions and improve public understanding of planetary science.
Europlanet is financed under the 'Research infrastructures' Activity area of the
Sixth Framework Programme (FP6).
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