Stellar Fossils in Pristine Meteorites Point to Ancient Stars That Died Before the Sun Formed

Some pristine meteorites contain a record of the original building blocks of the solar system, including grains that formed in ancient stars that died before the sun formed. One of the biggest challenges in studying these presolar grains is to determine the type of star each grain came from.

Nan Liu, research assistant professor of physics in Arts & Sciences at Washington University in St. Louis, is first author of a new study in Astrophysical Journal Letters that analyzes a diverse set of presolar grains with the goal of realizing their true stellar origins. Liu and her team used a state-of-the-art mass spectrometer called NanoSIMS to measure isotopes of a suite of elements including the N and Mg-Al isotopes in presolar silicon carbide (SiC) grains. By refining their analytical protocols and also utilizing a new-generation plasma ion source, the scientists were able to visualize their samples with better spatial resolution than could be accomplished by previous studies.

“Presolar grains have been embedded in meteorites for 4.6 billion years and are sometimes coated with solar materials on the surface,” Liu said. “Thanks to the improved spatial resolution, our team was able to see Al contamination attached on the surface of a grain and to obtain true stellar signatures by including signals only from the core of the grain during the data reduction.” The scientists sputtered the grains using an ion beam for extended periods of time to expose clean, interior grain surfaces for their isotopic analyses. The researchers found that the N isotope ratios of the same grain greatly increased after the grain was exposed to extended ion sputtering. Read more...

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