An international team of researchers has discovered tiny grains of sand from ancient supernova in two primitive meteorites.
Primitive carbonaceous chondrite LAP 031117 (NASA)
These two grains were identified in the primitive carbonaceous chondrites called LAP 031117 (discovered in 2003 at the LaPaz Ice Field, Antarctica) and Grove Mountains 021710 (found in 2003, also in Antarctica).
Because the grains have spookily similar isotopic compositions, the team speculates that they may have come from a single supernova, perhaps even the one whose explosion is thought to have triggered the formation of the Solar System.
The results appear in a paper in the Astrophysical Journal Letters (full paper from wustl.edu)
The first silica grain in a meteorite was found in 2009 by Prof Christine Floss of the Washington University in St. Louis and Dr Frank Stadermann. Their find was followed within the next few years by the discovery of four more grains. All of these grains were enriched in Oxygen-17 relative to Solar.
“This meant they had probably come from red giant or AGB stars,” said Prof Floss, co-author of ApJ L paper.
When Pierre Haenecour, a graduate student at the Washington University in St. Louis, who is the first author on the paper, began his graduate study with Prof Floss, she had him look at LAP 031117, a primitive meteorite that had been picked up in Antarctica by a U.S. team.
Haenecour found 138 presolar grains in the meteorite slice he examined and to his delight one of them was a silica grain. But this one was enriched in Oxygen-18, which meant it came from a core-collapse supernova, not a red giant.
Haenecour knew that another researcher had found a silica grain rich in Oxygen-18. Xuchao Zhao, now a scientist at the Institute of Geology and Geophysics in Beijing, China, found his grain in Grove Mountains 021710, a meteorite picked up in Antarctica by the Chinese Antarctic Research Expedition.
With two specks to go on, Haenecour tackled the difficult problem of calculating how a supernova might have produced silica grains. Before it explodes, a supernova is a giant onion, made up of concentric layers dominated by different elements.
Some theoretical models predicted that silica might be produced in massive oxygen-rich layers near the core of the supernova. But if silica grains could condense there, Haenecour and his colleagues thought, they should be enriched in Oxygen-16, not Oxygen-18.
Electron images of the silica grains found in LAP 031117 and GRV 021710 meteorites (Haenecour P et al)
They found they could reproduce the Oxygen-18 enrichment of the two grains by mixing small amounts of material from the Oxygen-rich inner zones and the Oxygen-18-rich helium/carbon zone with large amounts of material from the hydrogen envelope of the supernova.
“In fact, the mixing needed to produce the composition of the two grains was so similar that the grains might well come from the same supernova. Could it have been the supernova whose explosion is thought to have kick-started the collapse of the molecular cloud out of which the planets of the Solar System formed?” Haenecour said.
“How strange to think that two tiny grains of sand could be the humble bearers of such momentous tidings from so long ago and so far away.”
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Bibliographic information: Haenecour P et al. 2013. First laboratory observation of silica grains from core collapse supernovae. ApJ L 768; doi: 10.1088/2041-8205/768/1/L17
