2023-07-05 カリフォルニア工科大学(Caltech)
◆地球の内部からの岩石サンプルを分析した結果、揮発性-貧弱な分化微惑星の支配的な降着に続いて、揮発性に富む未分化隕石の降着の二次段階が続くという不均一な降着の歴史を明らかにしました。この研究は、他の地球型惑星である水星や金星の形成にも重要な予測を提供するとされている。地球形成の理論においても重要な貢献であり、地球の形成プロセスをより良く理解するためには、金星や水星などの内部を研究する必要があると指摘されている。
＜関連情報＞
- https://www.caltech.edu/about/news/earth-formed-from-dry-rocky-building-blocks
- https://www.science.org/doi/10.1126/sciadv.adg9213
I/Pu（ヨウ素/プルトニウム比）から、地球は主に揮発性の乏しい分化した準惑星から付加されたことが明らかになった。 I/Pu reveals Earth mainly accreted from volatile-poor differentiated planetesimals
Weiyi Liu,Yigang Zhang,François. L. H. Tissot,Guillaume Avice,Zhilin Ye, and Qing-Zhu Yin
Science Advances Published:5 Jul 2023
DOI:https://doi.org/10.1126/sciadv.adg9213
Abstract
The observation that mid-ocean ridge basalts had ~3× higher iodine/plutonium ratios (inferred from xenon isotopes) compared to ocean island basalts holds critical insights into Earth’s accretion. Understanding whether this difference stems from core formation alone or heterogeneous accretion is, however, hindered by the unknown geochemical behavior of plutonium during core formation. Here, we use first-principles molecular dynamics to quantify the metal-silicate partition coefficients of iodine and plutonium during core formation and find that both iodine and plutonium partly partition into metal liquid. Using multistage core formation modeling, we show that core formation alone is unlikely to explain the iodine/plutonium difference between mantle reservoirs. Instead, our results reveal a heterogeneous accretion history, whereby predominant accretion of volatile-poor differentiated planetesimals was followed by a secondary phase of accretion of volatile-rich undifferentiated meteorites. This implies that Earth inherited part of its volatiles, including its water, from late accretion of chondrites, with a notable carbonaceous chondrite contribution.
