April 21, 2013
Sand Grains In Meteorite May Have Come From Milky Way-Forming Supernova
redOrbit Staff & Wire Reports - Your Universe Online
Two tiny grains of silica discovered in primitive meteorites may have originated from the ancient supernova responsible for the formation of the solar system, according to new research published in the May 1 edition of Astrophysical Journal Letters.
The silica grains were discovered by scientists from Washington University in St. Louis (WUSTL) and the McDonnell Center for the Space Sciences, and was said to be “surprising” because the chemical compound is not one of the minerals expected to condense in stellar atmosphere.
According to the researchers, the two grains likely originated from a core-collapse supernova (a massive star which exploded at the end of its lifespan) and were found in meteorites from two different bodies of origin. Nonetheless, they have eerily similar isotopic compositions, leading the study authors to speculate they might have originated from the same supernova — perhaps even the one that started it all.
Prior to the 1960s, the majority of scientists believed the early Solar System had gotten so hot that pre-solar material would not have been able to survive. It wasn´t until 1987 University of Chicago scientists discovered miniature diamonds in a primitive meteorite.
Those diamonds were the first of several different types of elements to be discovered in this way, and researchers are able to tell they originated from ancient stars because of their highly unusual isotopic signatures.
The first silica grain was discovered in a meteorite in 2009 by Christine Floss, research professor of physics at WUSTL, and her now-deceased colleague Frank Stadermann. Prior to that time, many models of stellar evolution had predicted silicon would have been completely consumed by the formation of magnesium- or iron-rich silicates, which would leave none of the element left for silica formation.
The duo´s discovery was soon followed by the location of four additional silica grains, all of which were enriched in oxygen-17 when compared to the isotopic compositions of the Sun and the Milky Way´s planets. That meant they most likely originated from either red giant or asymptotic giant branch (AGB) stars, Floss said.
Enter Pierre Haenecour, a graduate student in Earth and Planetary Sciences and first author of the recently published paper. When he began his graduate studies, he was tasked with analyzing a primitive meteorite that had been recovered from Antarctica.
Using an ion microprobe, Haenecour discovered 138 pre-solar grains in the object, including a silica grain. However, this silica grain was enriched in oxygen-18, meaning it originated from a core-collapse supernova, not a red giant.
“He knew that another graduate student in the lab 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 a meteorite picked up in Antarctica by the Chinese Antarctic Research Expedition,” the university said in a statement. “With two specks to go on, Haenecour tackled the difficult problem of calculating how a supernova might have produced silica grains.
“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,” WUSTL added. “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.”