Surprising Ca isotopic anomalies in the early solar system
Date Issued
2010
Date
2010
Author(s)
Chen, Jang-Chung
Abstract
We have achieved higher precision for the measurement of Ca isotopic ratio by increasing the beam intensity to around 1.2nA. 42Ca/44Ca was normalized in order to correct the remaining ratios for fractionation. The two standard deviations in reproducibility for 40Ca/44Ca, 43Ca/44Ca, 46Ca/44Ca and 48Ca/44Ca were 1.5, 0.3, 7.5 and 0.7ε (ε ≡ 0.01%) respectively. The improved precision enabled us to not only confirm 48Ca anomalies up to 5.1ε in ordinary CAIs (Ca-Al-Inclusions) in meteorites but also search for Ca isotopic variation in bulk meteorites. Prior to this, 48Ca anomalies were only endemic to CAIs in carbonaceous chondrites. Surprisingly, our experiment revealed 48Ca deficit up to －2.3ε in achondrites relative to terrestrial samples. Because achondrites were presumably solidified from large scale melting on planetary bodies hundreds of km in size, they were not expected to present any detectable heterogeneities. On the other hand, the widespread 48Ca anomalies that correlate with 50Ti and 54Cr without large effects on the tiny 46Ca indicate that these nuclides originated from the rare neutron rich nuclear statistic equilibrium (n-rich NSE), not neutron capture. However, it remains unclear. As to how to keep this nucleosynthetic component made only in rare subset of type Ia supernovae from completely mixed in the solar system after the achondrites being solidified, it lends some support to the speculation that the solar system received some injected material from a nearby supernova that happened to explode after the solidification of achondrites but before the formation of terrestrial planets.
Subjects
Ca isotope measurement
meteorite
Type
thesis
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