[meteorite-list] Supernova Shrapnel Found In Meteorite

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 9 Sep 2010 09:53:38 -0700 (PDT)
Message-ID: <201009091653.o89GrcKt013336_at_zagami.jpl.nasa.gov>

Media Contact:
Steve Koppes
+1 773-702-8366
skoppes at uchicago.edu

Science Contact:
Nicolas Dauphas
+1 773-702-2930
dauphas at uchicago.edu

SUPERNOVA SHRAPNEL FOUND IN METEORITE
The University of Chicago
September 9, 2010

Scientists have identified the microscopic shrapnel of a nearby star
that exploded just before or during the birth of the solar system 4.5
billion years ago.

Faint traces of the supernova, found in a meteorite, account for the
mysterious variations in the chemical fingerprint of chromium found
from one planet and meteorite to another. University of Chicago
cosmochemist Nicolas Dauphas and eight co-authors report their
finding in the Sept. 10, 2010, issue of the Astrophysical
Journal.

Scientists formerly believed that chromium 54 and other elements and
their isotopic variations became evenly spread throughout the cloud of
gas and dust that collapsed to form the solar system. "It was a very
well-mixed soup," said Bradley Meyer, a professor of astronomy and
astrophysics at Clemson University who was not a co-author of the
study. "But it looks like some of the ingredients got in there and
didn't get completely homogenized, and that's a pretty interesting
result."

Scientists have known for four decades that a supernova probably
occurred approximately 4.5 billion years ago, possibly triggering the
birth of the Sun. Their evidence: traces of aluminum 26 and iron 60,
two short-lived isotopes found in meteorites but not on Earth.

These isotopes could have come from a Type II supernova, caused by the
core-collapse of a massive star. "It seems likely that at least one
massive star contributed material to the solar system or what was
going to become the solar systtem shortly before its birth," Meyer
said.

Researchers have already extracted many Type II supernova grains from
meteorites, but never from a Type Ia supernova. The latter type
involves the explosion of a small but extremely dense white-dwarf star
in a binary system, one in which two stars orbit each other. It should
now be possible to determine which type of supernova contributed the
chromium 54 to the Orgueil meteorite.

"The test will be to measure calcium 48," Dauphas said. "You can make
it in very large quantities in Type Ia, but it's very difficult to
produce in Type II." So if the grains are highly enriched in calcium
48, they no doubt came from a Type Ia supernova.

Cosmochemists have sought the carrier of chromium 54 for the last 20
years but only recently have instrumentation advances made it possible
to find it. Dauphas's own quest began in 2002, when he began the
painstaking meteorite sample-preparation process for the analysis he
was finally able to complete only last year.

Dauphas and his associates spent three weeks searching for chromium
54-enriched nanoparticles with an ion probe at the California
Institute of Technology. "Time is very precious on those instruments,
and getting three weeks of instrument time is not that easy," he said.

The researchers found a hint of an excess of the chromium-54 isotope
in their first session, but as luck would have it, they had to search
1,500 microscopic grains of the Orgueil and Murchison meteorites
before finding just one with definitely high levels.

The grain measured less than 100 nanometers in diameter -- 1,000 times
smaller than the diameter of a human hair. "This is smaller than all
the other kinds of presolar grains that have been documented before,
except for nanodiamonds that have been found here at the University of
Chicago," Dauphas said.

The findings suggest that a supernova sprayed a mass of finely grained
particles into the cloud of gas and dust that gave birth to the solar
system 4.5 billion years ago. Dynamical processes in the early sol
system then sorted these grains by size. These size-sorting processes
led the grains to become disproportionally incorporated into the
meteorites and planets newly forming around the Sun.

"It's remarkable that you can look at an isotope like chromium 54 and
potentially find out a whole lot about what happened in the very first
period of the solar system's formation," Meyer said.

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Citation:
"Neutron-rich chromium isotope anomalies in supernova nanoparticles,"
Sept. 10, 2010, Astrophysical Journal, by Nicolas Dauphas, Laurent
Remusat, James Chen, Mathieu Roskosz, Dimitri Papanastassiou, Julien
Stodolna, Yunbin Guan, Chi Ma, and John Eiler.

Funding:
National Aeronautics and Space Administration (NASA) and National
Science Foundation (NSF).
Received on Thu 09 Sep 2010 12:53:38 PM PDT