The composition of Solar system asteroids and Earth/Mars moons, and the Earth-Moon composition similarity

Abstract

[abridged] In the typical giant-impact scenario for the Moon formation most of the Moon's material originates from the impactor. Any Earth-impactor composition difference should, therefore, correspond to a comparable Earth-Moon composition difference. Analysis of Moon rocks shows a close Earth-Moon composition similarity, posing a challenge for the giant-impact scenario, given that impactors were thought to significantly differ in composition from the planets they impact. Here we use a large set of 140 simulations to show that the composition of impactors could be very similar to that of the planets they impact; in $4.9\%$-$18.2\%$ ($1.9\%$-$6.7\%$) of the cases the resulting composition of the Moon is consistent with the observations of ${\Delta }^{17}O<15$ (${\Delta }^{17}O<6$ ppm). These findings suggest that the Earth-Moon composition similarity could be resolved as to arise from the primordial Earth-impactor composition similarity. Note that although we find the likelihood for the suggested competing model of very high mass-ratio impacts (producing significant Earth-impactor composition mixing) is comparable ($<6.7\%$), this scenario also requires additional fine-tuned requirements of a very fast spinning Earth. Using the same simulations we also explore the composition of giant-impact formed Mars-moons as well as Vesta-like asteroids. We find that the Mars-moon composition difference should be large, but smaller than expected if the moons are captured asteroids. Finally, we find that the left-over planetesimals ('asteroids') in our simulations are frequently scattered far away from their initial positions, thus potentially explaining the mismatch between the current position and composition of the Vesta asteroid.

15 pages, 12 figures, resubmitted to MNRAS after referee comments. Abstract abridged for arXiv submission

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• Origin and dynamical evolution of the asteroid belt
• The role of multiple giant impacts in the formation of the Earth-Moon system
• Effect of Equation of State and Cutoff Density in Smoothed Particle Hydrodynamics Simulations of the Moon-Forming Giant Impact
• Moonfalls: Collisions between the Earth and its past moons
• 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
• Evidence of a primordial isotopic gradient in the inner region of the solar protoplanetary disc
• Realistic outcomes of moon-moon collisions in Lunar formation theory
• Asteroids fail to retain cometary impact signatures