[meteorite-list] Rare Meteorite Grains May be from Supernova That Sparked Solar System

[Ron Baalke]

http://www.space.com/20797-meteorite-supernova-solar-system.html

Rare Meteorite Grains May be from Supernova That Sparked Solar System
by Clara Moskowitz
space.com
24 April 2013 

Two surprising grains of sand in a pair of meteorites that landed on Earth 
suggest they were formed in a single supernova that occurred billions of 
years ago, new research suggests. These grains may even come from the same 
star explosion that sparked the formation of the solar system, scientists say.

Both meteorites were found in Antarctica, and appear to date from before the 
solar system was born 4.6 billion years ago. Each contains a single grain of 
silica (SiO2, which is the main ingredient of sand). The chemical signature of 
these grains is identical, and extremely rare - so rare, in fact, that scientists 
suspect both grains came from a single supernova. This type of supernova occurs 
when a massive star runs out of fuel for nuclear fusion and collapses in on itself 
in a giant explosion.

These are the first such grains found in primitive meteorites, and are distinct 
because of the type of oxygen contained in the silica. Previous research has 
uncovered a handful of space rocks containing silica grains enriched in oxygen-17, 
which is thought to be created by living stars. But a slightly heavier version of 
oxygen, called oxygen-18, was found in these two new grains. Oxygen-18 must be 
formed in a supernova. 

The silica grains are so small they are invisible to the naked eye. Using an 
instrument called a NanoSIMS 50 ion microprobe, which magnifies objects 20,000 
times, graduate student Pierre Haenecour of Washington University in St. Louis 
uncovered the single grain in one of the meteorites. The other was found 
by Xuchao Zhao, now a scientist at the Institute of Geology and Geophysics 
in Beijing, China, inside a meteorite discovered by the Chinese Antarctic 
Research Expedition.

Haenecour investigated just how the silica grains might have come to be, and found 
that their formation would have required a complex process of mixing material from 
various different layers of the star as it exploded.

Because the precise mixing required to create oxygen-18 is so specific, the 
researchers suspect that both silica grains originated in the same supernova. That 
supernova might even be the same explosion that gave rise to the solar system, the 
researchers speculated. Scientists think a shock wave from a supernova might have 
been the event that caused a rotating cloud of gas and dust to condense, eventually 
giving rise to the planets of our solar system.

As it exploded, the supernova also would have seeded the cloud with material, and 
some of that material may have ended up in the meteorites we find today.

The research is detailed in a paper published in the May 1 issue of Astrophysical 
Journal Letters.