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>A LOWER INITIAL ABUNDANCE OF SHORT-LIVED 41Ca IN THE EARLY SOLAR SYSTEM AND ITS IMPLICATIONS FOR SOLAR SYSTEM FORMATION
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A LOWER INITIAL ABUNDANCE OF SHORT-LIVED 41Ca IN THE EARLY SOLAR SYSTEM AND ITS IMPLICATIONS FOR SOLAR SYSTEM FORMATION
The short-lived radionuclide 41Ca plays an important role in constraining the immediate astrophysical environment and the formation timescale of the nascent solar system due to its extremely short half-life (0.1?Myr). Nearly 20?years ago, the initial ratio of 41Ca/40Ca in the solar system was determined to be (1.41 ± 0.14) × 10–8, primarily based on two Ca-Al-rich Inclusions (CAIs) from the CV chondrite Efremovka. With an advanced analytical technique for isotopic measurements, we reanalyzed the potassium isotopic compositions of the two Efremovka CAIs and inferred the initial ratios of 41Ca/40Ca to be (2.6 ± 0.9) × 10–9 and (1.4 ± 0.6) × 10–9 (2σ), a factor of 7-10 lower than the previously inferred value. Considering possible thermal processing that led to lower 26Al/27Al ratios in the two CAIs, we propose that the true solar system initial value of 41Ca/40Ca should have been ~4.2 × 10–9. Synchronicity could have existed between 26Al and 41Ca, indicating a uniform distribution of the two radionuclides at the time of CAI formation. The new initial 41Ca abundance is 4-16?times lower than the calculated value for steady-state galactic nucleosynthesis. Therefore, 41Ca could have originated as part of molecular cloud materials with a free decay time of 0.2-0.4?Myr. Alternative possibilities, such as a last-minute input from a stellar source and early solar system irradiation, could not be definitively ruled out. This underscores the need for more data from diverse CAIs to determine the true astrophysical origin of 41Ca.
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