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BBC NEWS
Meteorites carry ancient carbon
By Helen Briggs
BBC News science reporter
Meteorites that have fallen to Earth contain some of the most
primitive stuff of life, a new study has found.
Contrary to popular belief, they are packed with ancient carbon-rich
(organic) molecules that were essential for life to get started on
Earth.
Until now, it was thought such matter, which was formed before our
Solar System came into existence, could only be found in interstellar
dust.
The Carnegie Institution of Washington study is reported in Science
magazine.
It challenges the notion that the only way we can investigate our
molecular origins is to try to collect samples of unaltered cosmic
material from space - the driving force behind missions such as
Stardust.
Instead, the Carnegie team argues that primitive organic materials -
essentially unaltered components of the original building blocks of
the Solar System - can be found in the pieces of interplanetary rock
and metal that land on our planet.
Organic 'fingerprints'
The US scientists analysed six carbonaceous chondrite meteorites - the
oldest type known.
Using new techniques, the researchers looked at the relative
proportions of different types (isotopes) of nitrogen and hydrogen
atoms associated with the meteorites' organic matter.
Their analysis found regions where there was an excess of the heavier
forms of these elements - something also found in interstellar dust
grains.
It suggested, therefore, that the meteorites contained material that
had been largely unaltered since the time when the Solar System was
formed from the collapse of a giant cloud of gas and dust called the
solar nebula.
"It's amazing that pristine organic molecules associated with these
isotopes were able to survive the harsh and tumultuous conditions
present in the inner Solar System when the meteorites that contain
them came together," said Carnegie researcher Conel Alexander.
"It means that the parent bodies - the comets and asteroids - of these
seemingly different types of extraterrestrial material are more
similar in origin than previously believed."
Elusive time period
The discovery opens up a new window to study a long-gone era.
We could be looking at the remnants of precursor organic
molecules, formed in the interstellar medium before the Solar System
even existed Prof Ian Wright "Before, we could only explore minute
samples from interplanetary dust particles (IDPs)," said the lead
author of the Science paper, Henner Busemann.
"Our discovery now allows us to extract large amounts of this
material from meteorites, which are large and contain several percent
of carbon, instead of from IDPs, which are on the order of a million,
million times less massive."
The scientists believe that further investigation of meteorites may
yield enough material to perform experiments that would not be
possible with the tiny primitive organic grains from interplanetary
dust particles or cometary grains returned by the US space agency's
(Nasa) Stardust mission.
Pre-solar origin
UK planetary expert Ian Wright, of the Open University in Milton
Keynes, believes we now have the potential to be able to study pre-
solar organic molecules in the laboratory.
"That organic molecules in carbonaceous chondrites are, at least in
part, pre-solar in origin, is not a new idea," he told the BBC News
website.
"What is presented here are data that show that the distribution of
isotopic compositions within the organic complex is [highly varied].
"I guess it is possible that we could be looking at the remnants of
precursor organic molecules, formed in the interstellar medium before
the Solar System even existed, embedded in a complex that formed at a
later time (perhaps within the solar nebula itself)."
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/4973696.stm
Published: 2006/05/08 13:09:16 GMT
© BBC MMVI
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