Rocky asteroids and planets display nucleosynthetic isotope variations that are attributed to the heterogeneous distribution of stardust from different stellar sources in the solar protoplanetary disk. Here we report new high-precision palladium isotope data for six iron meteorite groups. The palladium data display smaller nucleosynthetic isotope variations than the more refractory neighbouring elements. Based on this observation, we present a model in which thermal destruction of interstellar dust in the inner Solar System results in an enrichment of s-process-dominated stardust in regions closer to the Sun. We propose that stardust is depleted in volatile elements due to incomplete condensation of these elements into dust around asymptotic giant branch stars. This led to the smaller nucleosynthetic variations for Pd reported here and the lack of such variations for more volatile elements. The smaller magnitude variations measured in heavier refractory elements suggest that material from high-metallicity asymptotic giant branch stars is the dominant source of stardust in the Solar System. These stars produce fewer heavy s-process elements (proton number Z ≥ 56) compared with the bulk Solar System composition.

岩石小行星和行星显示出核合成的同位素变化，这归因于太阳原行星盘中来自不同恒星源的星尘的异质分布。在这里，我们报告了六个铁陨石群的新的高精度钯同位素数据。钯数据显示出比更难熔的邻近元素更小的核合成同位素变化。基于此观察，我们提出了一个模型，其中内部太阳系中星际尘埃的热破坏导致s的富集。靠近太阳的区域中，以过程为主的星尘。我们建议，由于这些元素不完全凝结成渐近的巨型分支恒星周围的尘埃，因此它们中的挥发性元素耗尽了星尘。这导致此处报道的Pd的核合成变异较小，而挥发性较大的元素缺乏此类变异。在较重的耐火元素中测得的较小量级变化表明，来自高金属性渐近巨型分支星的物质是太阳系中星尘的主要来源。这些星产生较少的重小号-process元件（质子数Ž 与散装太阳系组合物相比≥56）。