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Isotopic anomalies in extraterrestrial grains
1Research School of Earth Sciences, Australian National University, Canberra.
Journal of the Royal Society of Western Australia
|March 1, 1996
Summary
Primitive meteorites preserve isotopic anomalies, revealing materials from distinct stellar nucleosynthesis sites. These anomalies offer insights into stellar evolution and element formation pathways.
Area of Science:
- Cosmochemistry
- Nuclear Astrophysics
- Planetary Science
Background:
- Isotopic compositions deviating from terrestrial ratios are termed anomalous.
- Primitive meteorites contain inclusions and grains with significant isotopic anomalies.
- These anomalies suggest the preservation of presolar materials from diverse stellar nucleosynthesis sites.
Purpose of the Study:
- To investigate the origins and implications of isotopic anomalies in primitive meteorites.
- To examine the preservation of presolar grains and their nucleosynthetic signatures.
- To understand the detailed nucleosynthetic pathways in stars through isotopic analysis.
Main Methods:
- Analysis of isotopic compositions in meteorite inclusions and grains using mass spectrometry.
- Characterization of refractory inclusions (Al, Ca, Ti, Mg oxides).
- Examination of carbonaceous phases (diamond, graphite) and silicon carbide (SiC) grains.
Main Results:
- Refractory inclusions show excesses in heavy isotopes of Ca, Ti, and Cr, linked to supernovae, and excess 26Mg from 26Al decay.
- Presolar SiC grains exhibit characteristic carbon and nitrogen isotopic signatures from stellar processes.
- A minor population of SiC (Grains X) shows evidence of supernova nucleosynthesis (26Al, 44Ti, 49V, 28Si excesses).
Conclusions:
- Isotopic anomalies in meteorites provide direct evidence of preserved presolar materials.
- These materials offer a window into distinct stellar nucleosynthesis sites and processes.
- The study of these anomalies enhances our understanding of element formation and stellar evolution.