Oxygen isotopic evidence for vigorous mixing during the Moon-forming Giant Impact (1603.04536v1)

Abstract: Earth and Moon are shown here to be composed of oxygen isotope reservoirs that are indistinguishable, with a difference in {\Delta}"17O of -1 +/- 5ppm (2se). Based on these data and our new planet formation simulations that include a realistic model for oxygen isotopic reservoirs, our results favor vigorous mixing during the giant impact and therefore a high-energy high- angular-momentum impact. The results indicate that the late veneer impactors had an average {\Delta}"17O within approximately 1 per mil of the terrestrial value, suggesting that these impactors were water rich.

• The paper demonstrates that oxygen isotope analyses reveal a minimal Δʹ′O difference (−1 ± 5 ppm) between Earth and Moon, indicating vigorous material mixing during the impact.
• It employs advanced simulations and refined sample techniques to challenge earlier models predicting distinct isotopic signatures from Theia's contributions.
• The findings refine lunar formation theories by establishing isotopic uniformity, which constrains the nature of later accretion events and impactor sources.

Insights into the Moon-forming Giant Impact: An Analysis of Oxygen Isotopic Evidence

The research paper "Oxygen isotopic evidence for vigorous mixing during the Moon-forming Giant Impact" presents a comprehensive study of oxygen isotopic compositions, providing empirical data that examines the origin of the Moon through the lens of isotopic similarities between the Earth and Moon. This study dissects traditional models of lunar formation and uses oxygen isotope data to propose an alternate understanding, emphasizing the oxygen isotopic uniformity between the two celestial bodies.

The paper initiates by discussing the historical context and scientific challenges regarding the Giant Impact Hypothesis for the Moon's formation. This hypothesis suggests that a Mars-sized planetary body, Theia, collided with the early Earth, leading to the formation of the Moon. The authors highlight previous expectations of a measurable isotopic distinction between Earth and Moon, as early models required a dominance of Theia's materials in the Moon's makeup. However, recent discoveries showed no significant difference in isotopic ratios, aligning the isotopic features of Earth and its satellite.

Central to this study, Young et al. provide robust isotopic analyses derived from both lunar and terrestrial samples. Their results indicate a minimal difference of Δʹ′O values, documented as −1 +/− 5 ppm between Earth and Moon. This is a critical finding, advocating a scenario of thorough mixing during the impact event, contrary to prior hypotheses that suggested a composition primarily influenced by Theia. The authors utilized advanced simulation models that integrate realistic isotopic reservoirs and thoroughly assess the implications of high-energy, high-angular-momentum impact events on the post-collision mixing states.

Several simulations, including those based on the Grand Tack scenario, form part of this exploration, highlighting the isotopic composition evolution from numerous proto-planetary embryos and planetesimals, proposing homogeneity in isotopic distribution across larger planet formations like Earth and smaller variance for planetesimals like Mars.

Importantly, the study addresses previous assertions of a 12 ppm difference in Δʹ′O between Earth and Moon by Herwartz et al., providing greater precision through improved sample analysis techniques. The results refute these earlier claims, presenting a meticulous comparison of isotopic data that aligns with identical isotopic reservoirs for both bodies.

The implications of this isotopic convergence are profound. It suggests the Moon-forming impact facilitated complete homogenization of Theia and proto-Earth materials, effectively eliminating isotopic distinctions. Further, these findings impose constraints on the nature of late veneer impactors contributing to Earth and Moon, favoring those with oxygen isotopic ratios akin to Earth's, such as enstatite chondrites.

The conclusions drawn from this study pose substantial questions about primordial solar system dynamics and encourage the reassessment of models concerning planetary accretion processes. The elimination of isotopic differences as evidence for thorough mixing amplifies considerations of high-energy collisional events and the isotopic constitution of impacting bodies in early solar system development.

Future research virtues entail fine-tuning the chronological dating of planetary impacts through isotopic analysis, potentially uncovering nuanced relationships between terrestrial planets and their satellite systems. Moreover, delineating further isotopic variations with precision could unravel the intricate history of planetary formation and chemical differentiation across the solar system. This paper thus lays groundwork for theoretical advancements in lunar origin studies while presenting conclusive evidence for isotopic uniformity between Earth and the Moon.