"Planetary" noble gas components and the nucleosynthetic history of solar system material
"Planetary" noble gas components and the nucleosynthetic history of solar system material
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“行星”惰性气体成分与太阳系物质的核合成历史
DOI：
10.1016/j.gca.2009.09.015
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发表时间：
2010
影响因子：
5
通讯作者：
Gilmour J
中科院分区：
文献类型：
--
作者：
Gilmour J
提出了能够解释行星惰性气体组分“Q”和“P3”(广泛存在于原始陨石中)的同位素组成与太阳风采样的太阳系平均物质之间的差异的模型，并讨论了它们的意义。Q气体中存在着少量的、数量不一的已知太阳系前组分和129I衰变产生的129Xe，同时还有一种太阳成分已经被质量分馏。这些最有可能发生在母体处理过程中的混合或在分析过程中从保持性较差的相中共释放。因此，原始陨石的重惰性气体收支由一种来自太阳系平均组成物质的成分主导。相比之下，P3似乎最好地解释为一种太阳系前成分，与随后随着新合成材料的加入而演化为太阳成分的大宗物质的分离一致。对Kr-P3的研究发现，这种加成具有弱S过程的特征，并证明了第二个过程，即贡献S过程中没有产生的氪的同位素(剩余同位素)，一定也在储层演化为太阳成分时增加了物质。S过程所需的132Xe和84Kr的总贡献至少占当前预算的1%，剩余氪“组分”的贡献也是如此。虽然P3的浓度随母体处理程度的不同而不同，但在那些保留P3特征的最小处理陨石中，与P3相关的129I衰变产生的129Xe过剩浓度大致保持不变(ALH77307除外)。这对早期太阳系P3中活着的129I碘和氙气的不同化学行为有一个自然的解释。在太阳系早期的P3中，Live129I的存在施加了一个松散的约束，即在太阳系形成之前，P3组分从低于∼100Myr的母库中分离出来。从P3气体到太阳成分的演化模型要求剩余的氪同位素不是也合成129I的传统r过程的产物。氪剩余同位素的合成和重元素r过程的不同位置与贫金属星的观测结果一致，但与为解释182Hf和129I系统之间的变化而调用的两个r过程不一致。由于微弱的S过程被认为是P3储集层演化为太阳成分时贡献的S过程物质的来源，因此承载它的大质量恒星也可能包含合成剩余氪同位素的过程。最近附近大质量恒星的存在与太阳系形成环境的一幅新兴图景是一致的。
Models capable of explaining the differences between the isotopic compositions of the planetary noble gas components “Q” and “P3” (widespread in primitive meteorites) and average solar system material as sampled by the solar wind are presented, and their implications discussed. Small, variable amounts of known presolar components and129Xe from129I decay are present in Q gases alongside a solar composition that has been mass fractionated. These most likely arise either from mixing during parent body processing or co-release from poorly retentive phases during analysis. Thus the heavy noble gas budget of primitive meteorites is dominated by a component derived from material with the average composition of the solar system. In contrast, P3 seems best explained as a presolar component, consistent with isolation from bulk material that subsequently evolved to the solar composition as newly synthesised material was added. Examination of Kr-P3 identifies the addition as having had the signature of the weak s-process, and demonstrates that a second process that contributes the isotopes of krypton not produced in the s-process (residual isotopes) must also have added material to the reservoir as it evolved to the solar composition. Total s-process contributions required of132Xe and84Kr are at least ∼1% of the present budget, as is that of the residual krypton “component”. While concentrations of P3 vary with extents of parent body processing, concentrations of129Xe excess from129I decay associated with P3 are roughly constant in those least processed meteorites that retain a P3 signature (apart from ALH77307). This has a natural explanation in the different chemical behaviours of iodine and xenon if129I was alive in P3 in the early solar system. The presence of live129I in P3 in the early solar system imposes a loose constraint that the P3 component was isolated from a parent reservoir less than ∼100Myr before the formation of the solar system. The model of evolution from P3 gases to the solar composition requires that residual krypton isotopes are not products of a conventional r-process that also synthesises129I. Separate sites for synthesis of residual isotopes of krypton and the heavy element r-process are consistent with observations of metal poor stars, but do not correspond to the two r-processes invoked to account for variations between the182Hf and129I systems. Since the weak s-process is implicated as the source of the s-process material contributed as the P3 reservoir evolved to a solar composition, the massive stars that host it may also host the process that synthesises residual krypton isotopes. The recent presence of nearby massive stars is consistent with an emerging picture of the environment of solar system formation.
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DOI：
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