`Yukon meteorite dates back to origins of the solar system
Tom Spears
The Ottawa Citizen
http://www.ottawacitizen.com/national/010402/5019000.html
Dave Chidley, The London Free Press / University of Western Ontario
professor Peter Brown with a Tagish Lake meteorite, which may be one of
the most primitive solar system materials ever examined.
The 200-tonne meteor that blew up over the Yukon last year is turning
out to be older than any other known meteorite, older than our planet,
probably the oldest matter ever to come to Earth.
Chunks of space rock pulled from a lake on the Yukon-British Columbia
border probably formed as other planets did, condensing from the giant
cloud of gas that swirled around our sun as it first came into
existence.
One thing looks certain: The Tagish Lake meteorite, named after the
frozen lake it hit, was once rich in water, yet not so rich that water
washed away the interesting details.
The clumps of grey-black matter may also be the oldest meteorite ever
discovered, older than Earth, and therefore our best look at the raw
materials from which our solar system was built.
It's also rich in organic molecules, the building blocks of proteins,
DNA and other molecules in all living things.
Months of analysis of the dark grey lumps of Tagish Lake rock have shown
it came from a watery environment even though the meteorite itself is
older than Earth or the rest of our solar system.
Five to six per cent of the 12 kilograms of Tagish Lake rocks are
carbonate materials -- minerals similar to clays and limestones on
Earth, which are formed as water acts on other metals and minerals.
"The implication is that this comes from an asteroid rich in water,"
says Richard Herd, curator of Canada's national meteorite collection.
"Was there a component of ice in this meteorite? There was 200 tonnes of
something that hit the atmosphere."
Unfortunately, the incoming space rock exploded in spectacular fashion
25 kilometres above the ground, scattering fragments all over, and the
heat may have vaporized any ice. If five-billion-year-old ice did
survive, it would have been lost in the ordinary snow and ice on the
ground.
Still, enough survived to thrill scientists, who have just finished
going over the first round of Tagish Lake studies at a conference in
Houston.
It looks like the oldest meteorite ever found, says Peter Brown of the
University of Western Ontario. Younger meteorites have often been
compressed or heated by planet-forming forces into solid rocks and
metals. But Tagish Lake is a loose material that falls apart when
handled. Meteorites like this are rare because they simply decay into
soil if they aren't found promptly.
"Tagish Lake is telling us that for the first time we have the building
blocks (of matter) that went into the outer planets," he said. It almost
certainly formed from gases that swirled around our sun before they
condensed into planets.
"If there's anything of interest about Tagish Lake, it's that it isn't
like anything else," Mr. Herd said.
"It's a strange meteorite. It doesn't fit," he said. There are plenty of
other "chondrites" -- bodies of very primitive material formed when a
star is still young and planets haven't yet formed.
But Tagish Lake doesn't match the picture of other chondrites. For one
thing, it contains no amino acids or polyaromatic hydrocarbons (PAHs) --
tarry, sticky organic compounds often found in this type of space rock.
These are organic molecules of intense interest to astronomers because
some of the chemical compounds in them are identical to chemicals in our
own cells.
"It can't be pigeonholed, slotted into any category," he said, but
that's a good thing: "Science advances when things can't be
pigeonholed."
Tagish Lake's meteorite does contain "primitive" organic chemicals that
could be used to build amino acids, Mr. Herd says.
`
Leslee ^i^