Brief Follow-up on Recent Studies of Theia's Accretion

Abstract

Kaib & Cowan (2015) recently used terrestrial planet formation simulations to conclude that the moon-forming impactor (Theia) had only a ~5% or less chance of having the same oxygen isotope composition as Earth, while Mastrobuono-Battisti et al. (2015) used seemingly similar simulations and methods to arrive at a higher value of ~20% or more. Here we derive the results of both papers from a single set of simulations. Compared to Kaib & Cowan (2015), the analysis of Mastrobuono-Battisti et al. (2015) systematically yields more massive Theia analogs and imposes flatter isotopic gradients across the original protoplanetary disk. Both of these effects diminish isotopic differences between Earth and Theia analogs. While it is notoriously difficult to produce systems resembling our actual terrestrial planets, the analysis of Kaib & Cowan (2015) more often selects and analyzes Earth and Mars analogs at orbital locations near the real planets. Given this, we conclude that the greater isotopic differences between Earth and Theia found in Kaib & Cowan (2015) better reflect the predictions of terrestrial planet formation models. Finally, although simulation uncertainties and a terrestrial contribution to Moon formation enhance the fraction of Theia analogs consistent with the canonical giant impact hypothesis, this fraction still remains in the 5-8% range.

arXiv comment5 pages, 4 figures, accepted to Icarus

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Cited by in corpus (6)

• Melting and Mixing States of the Earth's Mantle after the Moon-Forming Impact
• The Lunar Gravitational-wave Antenna: Mission Studies and Science Case
• The composition of Solar system asteroids and Earth/Mars moons, and the Earth-Moon composition similarity
• Accretion regions of meteorite parent bodies inferred from a two-endmember isotopic mixing model
• A Systematic Survey of Moon-Forming Giant Impacts. II. Rotating bodies
• Earth accreted increasingly oxidized material as it grew constraining Theia to be small and relatively oxidized