[meteorite-list] One of the best of the 2008 TC3 articles

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Wed, 25 Mar 2009 17:34:35 -0500
Message-ID: <p8cls49s350njl80k9umhm9kqvhui97mkt_at_4ax.com>

Okay, this needs to go on that list from a few days ago of "most important
meteorites."

http://www.livescience.com/space/090325-asteroid-meteorites.html


Space 'Rosetta Stone' Unlike Anything Seen Before

By Andrea Thompson, Senior Writer

posted: 25 March 2009 02:00 pm ET

Meteorite fragments of the first asteroid ever spotted in space before it
slammed into Earth's atmosphere last year were recovered by scientists from the
deserts of Sudan.

These precious pieces of space rock, described in a study detailed in the March
26 issue of the journal Nature, could be an important key to classifying
meteorites and asteroids and determining exactly how they formed.

The asteroid was detected by the automated Catalina Sky Survey telescope at
Mount Lemmon , Ariz., on Oct. 6, 2008. Just 19 hours after it was spotted, it
collided with Earth's atmosphere and exploded 23 miles (37 kilometers) above the
Nubian Desert of northern Sudan.

Because it exploded so high over Earth's surface, no chunks of it were expected
to have made it to the ground. Witnesses in Sudan described seeing a fireball,
which ended abruptly.

But Peter Jenniskens, a meteor astronomer with the SETI Institute's Carl Sagan
Center, thought it would be possible to find some fragments of the bolide. Along
with Muawia Shaddad of the University of Khartoum and students and staff,
Jenniskens followed the asteroid's approach trajectory and found 47 meteorites
strewn across an 18-mile (29-km) stretch of the Nubian Desert.

"This was an extraordinary opportunity, for the first time, to bring into the
lab actual pieces of an asteroid we had seen in space," Jenniskens said.

Classification

Astronomers were able to detect the sunlight reflected off the car-sized
asteroid (much smaller than the one thought to have wiped out the dinosaurs)
while it was still hurtling through space. Looking at the signature of light, or
spectra of space rocks is the only way scientists have had of dividing asteroids
into broad categories based on the limited information the technique gives on
composition.

However, layers of dust stuck to the surfaces of the asteroids can scatter light
in unpredictable ways and may not show what type of rock lies underneath. This
can also make it difficult to match up asteroids with meteorites found on Earth
? that's why this new discovery comes in so handy.

Both the asteroid, dubbed 2008 TC3, and its meteoric fragments indicate that it
could belong to the so-called F-class asteroids.

"F-class asteroids were long a mystery," said SETI planetary spectroscopist
Janice Bishop. "Astronomers have measured their unique spectral properties with
telescopes, but prior to 2008 TC3 there was no corresponding meteorite class, no
rocks we could look at in the lab."

Cooked carbon

The chemical makeup of the meteorite fragments, collectively known as "Almahata
Sitta," shows that they belong to a rare class of meteorites called ureilites,
which may all have come from the same original parent body. Though what that
parent body was, scientists do not know.

"The recovered meteorites were unlike anything in our meteorite collections up
to that point," Jenniskens said.

The meteorites are made of very dark, porous material that is highly fragile
(which explains why the bolide exploded so high up in the atmosphere).

The carbon content of the meteorites shows that at some point in the past, they
were subjected to very high temperatures.

"Without a doubt, of all the meteorites that we've ever studied, the carbon in
this one has been cooked to the greatest extent," said study team member Andrew
Steele of the Carnegie Institution in Washington, D.C. "Very cooked,
graphite-like carbon is the main constituent of the carbon in this meteorite."

Steele also found nanodiamonds in the meteorite, which could provide clues as to
whether heating was caused by impacts to the parent asteroid or by some other
process.

Rosetta Stone

Having spectral and laboratory information on the meteorites and their parent
asteroid will help scientists better identify ureilite asteroids still circling
in space.

"2008 TC3 could serve as a Rosetta Stone, providing us with essential clues to
the processes that built Earth and its planetary siblings," said study team
member Rocco Mancinelli, also of SETI.

One known asteroid with a similar spectrum, the 2.6-km wide 1998 KU2, has
already been identified as a possible source for the smaller asteroid 2008 TC3
that impacted Earth.

With efforts such as the Pan-STARRS project sweeping the skies in search of
other near-Earth asteroids, Jenniskens expects that more events like 2008 TC3
will happen.

"I look forward to getting the next call from the next person to spot one of
these," he said. "I would love to travel to the impact area in time to see the
fireball in the sky, study its breakup and recover the pieces. If it's big
enough, we may well find other fragile materials not yet in our meteorite
collections."
Received on Wed 25 Mar 2009 06:34:35 PM PDT