2026-09-30 コペンハーゲン大学（UCPH）
＜関連情報＞
- https://news.ku.dk/all_news/2026/09/new-study-rekindles-contested-question-earth-and-mars-had-different-origins/
- https://www.nature.com/articles/s41550-026-02984-6
岩石惑星における揮発性物質の枯渇は、ハイブリッド集積の化学的特徴である Volatile depletion in rocky planets as a chemical fingerprint of hybrid accretion
Haiyang S. Wang, Anders Johansen, Ziyan Xu, Marie-Luise Steinmeyer, Michiel Lambrechts, Elishevah van Kooten, Chao-Chin Yang, Zhaohuan Zhu, Dante S. Lauretta & Martin Bizzarro
Nature Astronomy Published:25 September 2026
DOI:https://doi.org/10.1038/s41550-026-02984-6
Abstract
Volatile depletion in rocky planets relative to their host stars is commonplace in both the Solar System and exoplanetary systems, yet the connections between planet formation and composition remain elusive. Here we model devolatilization during pebble accretion in combination with collisional growth from volatile-depleted planetesimals to explore the formation pathways of Earth and Mars. Using Bayesian inference, we found that bulk silicate Earth is best reproduced by ≳75% contribution from two protoplanets formed via pebble accretion, supplemented by up to ~25% material from planetesimals that are compositionally akin to the asteroid Vesta. Using instead a planetesimal volatile-depletion curve that is not observed among known meteorite parent bodies would allow the planetesimal contribution to reach %. In comparison, bulk silicate Mars reflects 27 ± 5% pebble-accreted material and 73 ± 5% Vesta-like planetesimals. We identified volatile depletion as a chemical fingerprint of hybrid accretion, in which both pebble accretion and collisional assembly contribute to terrestrial planet growth. By quantitatively linking formation pathways to volatile budgets, our findings demonstrate how planetary accretion histories can be inferred from elemental signatures, with broad implications for interpreting the chemical diversity of rocky exoplanets.
