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.

arXiv comment15 pages, 12 figures, published in ApJL. Animations available at https://www.youtube.com/channel/UCGnGqCiYLWvYN992mBkBnhg/

References in corpus (22)

• Equilibration in the Aftermath of the Lunar-Forming Giant Impact
• The origin of the Moon within a terrestrial synestia
• Gasoline2: A Modern SPH Code
• Melting and Mixing States of the Earth's Mantle after the Moon-Forming Impact
• A hit-and-run Giant Impact scenario
• Multiple Impact Origin for the Moon
• Tidal evolution of the Moon from a high-obliquity, high-angular-momentum Earth
• Lunar accretion from a Roche-interior fluid disk
• On the origin and composition of Theia: Constraints from new models of the Giant Impact
• Resolution Dependence of Disruptive Collisions between Planetesimals in the Gravity Regime
• Planetary Giant Impacts: Convergence of High-Resolution Simulations using Efficient Spherical Initial Conditions and SWIFT
• The Shock Physics of Giant Impacts: Key Requirements for the Equations of State
• Atmospheric Erosion by Giant Impacts onto Terrestrial Planets
• Collisionless Encounters and the Origin of the Lunar Inclination
• Tidal Evolution of the Evection Resonance/Quasi-Resonance and the Angular Momentum of the Earth-Moon System
• Enhanced mixing in giant impact simulations with a new Lagrangian method
• Primordial Earth mantle heterogeneity caused by the Moon-forming giant impact
• Unconvergence of Very Large Scale GI Simulations
• The effect of pre-impact spin on the Moon-forming collision
• Collision Chains among the Terrestrial Planets. III. Formation of the Moon
• The composition of Solar system asteroids and Earth/Mars moons, and the Earth-Moon composition similarity
• The role of multiple giant impacts in the formation of the Earth-Moon system

Cited by in corpus (12)

• SWIFT: A modern highly-parallel gravity and smoothed particle hydrodynamics solver for astrophysical and cosmological applications
• 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