Immediate origin of the Moon as a post-impact satellite

Abstract

The Moon is traditionally thought to have coalesced from the debris ejected by a giant impact onto the early Earth. However, such models struggle to explain the similar isotopic compositions of Earth and lunar rocks at the same time as the system's angular momentum, and the details of potential impact scenarios are hotly debated. Above a high resolution threshold for simulations, we find that giant impacts can immediately place a satellite with similar mass and iron content to the Moon into orbit far outside the Earth's Roche limit. Even satellites that initially pass within the Roche limit can reliably and predictably survive, by being partially stripped then torqued onto wider, stable orbits. Furthermore, the outer layers of these directly formed satellites are molten over cooler interiors and are composed of around 60% proto-Earth material. This could alleviate the tension between the Moon's Earth-like isotopic composition and the different signature expected for the impactor. Immediate formation opens up new options for the Moon's early orbit and evolution, including the possibility of a highly tilted orbit to explain the lunar inclination, and offers a simpler, single-stage scenario for the origin of the Moon.

15 pages, 12 figures, published in ApJL. Animations available at https://www.youtube.com/channel/UCGnGqCiYLWvYN992mBkBnhg/

References in corpus (6)

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• Melting and Mixing States of the Earth's Mantle after the Moon-Forming Impact
• Multiple Impact Origin for the Moon
• On the origin and composition of Theia: Constraints from new models of the Giant Impact
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Cited by in corpus (12)

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• Origin of Mars's moons by disruptive partial capture of an asteroid
• Composition, Structure and Origin of the Moon
• Effect of Equation of State and Cutoff Density in Smoothed Particle Hydrodynamics Simulations of the Moon-Forming Giant Impact
• REMIX SPH -- improving mixing in smoothed particle hydrodynamics simulations using a generalised, material-independent approach
• A scaling relation for core heating by giant impacts and implications for dynamo onset
• On the origin of Jupiter's fuzzy core: constraints from N-body, impact and evolution simulations
• A Systematic Survey of Moon-Forming Giant Impacts. II. Rotating bodies
• The Limited Role of the Streaming Instability During Moon and Exomoon Formation
• Exploring the catastrophic regime: thermodynamics and disintegration in head-on planetary collisions
• No dilute core produced in simulations of giant impacts on to Jupiter
• Re-accretion of Giant Impact Ejecta Can Drive Significant Atmospheric Erosion on Terrestrial Planets