[PPS10-12] Origin and evolution of distinct isotopic variabilities for Sr, Mo, and Nd within inner and outer solar system
★Invited Papers
キーワード：CCs vs NCs、核合成起源同位体異常、初期太陽系
Recent findings of nucleosynthetic isotope anomalies in bulk meteorites, characterized by mass-independent isotopic deviation from terrestrial materials, indicate planetary-scale heterogeneities in the multi-elemental isotope systems of refractory heavy elements. Additionally, the findings overturned the traditional classification of meteorites based on their textures and chemical compositions. For instance, carbonaceous chondrites (CCs) and other meteorites (noncarbonaceous meteorites; NCs) form distinct clusters in the isotope spaces including ε50Ti-ε54Cr, Δ17O-ε54Cr, and µ95Mo-µ94Mo, suggesting that the source materials feeding the CC and NC parent bodies were widely separated in the early solar system, with larger heliocentric distance for CCs than NCs [1-2]. Furthermore, different classes of meteorites within the CC and NC groups show variabilities in isotope compositions for some heavy elements. These isotopic characteristics recorded in meteorites would reflect the dynamic history of material transport and mixing in the early solar system.
We have investigated the variabilities of the isotopic compositions for Sr, Nd, and Mo in CC and NC meteorites [3-4]. The CCs are characterized to form an s-process mixing line in the µ95Mo–µ94Mo space. As opposed to this observation, the data of CCs deviate from the s-process mixing line in the µ84Sr–µ150Nd space. The inconsistency could be caused by the difference in the chemical characteristics of Mo (siderophile elements) and Sr-Nd (lithophile elements), specifically for the non-uniform distribution in some CCs (e.g., CV chondrites) of isotopically anomalous calcium-aluminum-rich inclusions (CAIs) in which large proportions of Sr and Nd are hosted. In fact, the data for CAI-subtracted CCs are plotted on the s-process mixing line in the µ84Sr-µ150Nd space. Therefore, the isotope variabilities for Sr, Nd, and Mo within the CCs indicate that s-process matter distributed heterogeneously throughout various chondritic components in the different outer solar system materials.
In contrast, the data for NCs are relatively homogeneous and plotted on the s-process mixing line in the µ84Sr-µ150Nd space. Unlike this observation, the NCs show Mo isotope variability in the µ95Mo-µ94Mo space. The Mo isotope variability for NCs suggests the presence of two end-member components in the NC reservoir (i.e., NC-A and NC-B), where the involvement of an additional nucleosynthetic component other than the s-process is required. Two models are proposed to account for the Mo isotopic variation within the NCs; (i) Mo isotopic composition of the NC region changed gradually from NC-A- to NC-B-like components as a function of the heliocentric distance, or (ii) a fractionation process involving chondritic matrix and metal, which most likely occurred locally in time and/or space, has generated the Mo isotope variability in the NC region.
[1] Warren, 2011, EPSL 311, 93. [2] Kruijer et al., 2017, PNAS 114, 6712. [3] Fukai and Yokoyama, 2019, ApJ 879, 79. [4] Yokoyama et al., 2019, ApJ 883, 62.
We have investigated the variabilities of the isotopic compositions for Sr, Nd, and Mo in CC and NC meteorites [3-4]. The CCs are characterized to form an s-process mixing line in the µ95Mo–µ94Mo space. As opposed to this observation, the data of CCs deviate from the s-process mixing line in the µ84Sr–µ150Nd space. The inconsistency could be caused by the difference in the chemical characteristics of Mo (siderophile elements) and Sr-Nd (lithophile elements), specifically for the non-uniform distribution in some CCs (e.g., CV chondrites) of isotopically anomalous calcium-aluminum-rich inclusions (CAIs) in which large proportions of Sr and Nd are hosted. In fact, the data for CAI-subtracted CCs are plotted on the s-process mixing line in the µ84Sr-µ150Nd space. Therefore, the isotope variabilities for Sr, Nd, and Mo within the CCs indicate that s-process matter distributed heterogeneously throughout various chondritic components in the different outer solar system materials.
In contrast, the data for NCs are relatively homogeneous and plotted on the s-process mixing line in the µ84Sr-µ150Nd space. Unlike this observation, the NCs show Mo isotope variability in the µ95Mo-µ94Mo space. The Mo isotope variability for NCs suggests the presence of two end-member components in the NC reservoir (i.e., NC-A and NC-B), where the involvement of an additional nucleosynthetic component other than the s-process is required. Two models are proposed to account for the Mo isotopic variation within the NCs; (i) Mo isotopic composition of the NC region changed gradually from NC-A- to NC-B-like components as a function of the heliocentric distance, or (ii) a fractionation process involving chondritic matrix and metal, which most likely occurred locally in time and/or space, has generated the Mo isotope variability in the NC region.
[1] Warren, 2011, EPSL 311, 93. [2] Kruijer et al., 2017, PNAS 114, 6712. [3] Fukai and Yokoyama, 2019, ApJ 879, 79. [4] Yokoyama et al., 2019, ApJ 883, 62.