2026-09-08 アリゾナ大学
Artist’s impression of the giant impact between the early Earth and “Theia,” a Mars-sized body believed to have resulted in the formation of the moon. NASA/JPL-CalTech/T. Pyle
＜関連情報＞
- https://news.arizona.edu/news/soft-and-stretchy-or-rock-solid-new-modeling-study-sheds-light-how-earth-got-its-moon
- https://iopscience.iop.org/article/10.3847/2041-8213/ae91e9
衝突による無傷の月の捕獲は強度に依存する Collisional Capture of an Intact Moon Depends on Strength
C. Adeene Denton, Erik Asphaug, Namya Baijal, and Robert E. Melikyan
The Astrophysical Journal Letters Published: 2026 September 1
DOI:10.3847/2041-8213/ae91e9
Abstract
The canonical giant impact hypothesis suggests that the proto-Earth’s collision with a differentiated Mars-sized planet, Theia, produced an iron-poor debris disk that accreted to form the Moon. Here, we revisit that hypothesis, for the first time using smoothed-particle hydrodynamics (SPH) simulations with realistic strength. Although negligible compared to stresses in the deep interior, strength in the outer hundreds of kilometers of Theia is shown to hinder its deformation, which alters the transfer of momentum, leading to fundamental differences in Moon formation. For one set of otherwise identical canonical impact parameters, a hot but solid Theia produces an intact Moon, whereas a colder, stronger Theia—i.e., a later Moon-formation scenario—produces a classic protolunar disk. These completely different scenarios arise from different mechanical responses due to temperature and establish an important new connection between giant impact dynamics and the timing and geochemistry of lunar formation.
