[PPS02-P01] Distribution of 54Cr Isotope Anomalies in Asteroid Belt
Keywords:Isotopic Anomaly, Solar Nebula
In this study, a model that may reproduce the observed anomalies of 54Cr starting from the inhomogeneous molecular cloud core is examined.
Model: It is assumed that isotopically heterogeneous dust grains are inhomogeneously distributed in the initial molecular cloud core; especially, 54Cr-rich grains are concentrated in the central part of the cloud core. Then, the concentration of 54Cr-rich grains is calculated numerically as a function of the time and the place in the solar nebula. Model parameters are the initial angular velocity of the molecular cloud core omega, which determines the size of growing solar nebula, and the strength of the gas turbulence in the solar nebula alpha, which controls the radial flow of the gas and the diffusive motion of dust grains. The mass infall from the molecular cloud core lasts 0.4 Myr.
Results: A typical result is as follows. When omega = 3×10-15 s-1 and alpha = 10-4, in the early phase (< 0.4 Myr), the concentration decreases as time because the infall of new dust grains from the cloud core dilutes the concentration of 54Cr rich dust grains. Later (> 0.4 Myr), the concentration increases because of the diffusive motion in the nebula. These features are consistent with observations [1, 2].
Summary: We examined the possibility that an inhomogeneous molecular cloud core could generate the inhomogeneous and time dependent distribution of 54Cr-rich dust grains in the asteroid belt. We found that indeed the mechanism may work. The isotope anomalies may be caused by the inhomogeneous initial molecular cloud and by the incomplete mixing of dust grains in the solar nebula.
References:  Sugiura and Fujiya (2014) Meteorit. and Planet. Sci. 49, 772-787.  Trinquier et al. (2009) Science 324, 374-376.  Kuffmeier, M. et al. (2016), Astrophysical Journal 826, id. 22.