[meteorite-list] Supernova Shrapnel Found in Meteorite

[MEM]

Yet another meteorite related news item.  Check your specimens for chromium 54 
grains and see if you've hit the lottery for pre-pre-solar grains!  They will be 
magnetic but at 100 nm not somehting you'll see with the eye alone.
Elton

Supernova Shrapnel Found in Meteorite
ScienceDaily (Sep. 14, 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 late 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 system 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  solar 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.