The structure of terrestrial bodies: Impact heating, corotation limits and synestias

Abstract

During accretion, terrestrial bodies attain a wide range of thermal and rotational states, which are accompanied by significant changes in physical structure (size, shape, pressure and temperature profile, etc.). However, variations in structure have been neglected in most studies of rocky planet formation and evolution. Here, we present a new code, HERCULES, that solves for the equilibrium structure of planets as a series of overlapping constant-density spheroids. Using HERCULES and a smoothed particle hydrodynamics code, we show that Earth-like bodies display a dramatic range of morphologies. For any rotating planetary body, there is a thermal limit beyond which the rotational velocity at the equator intersects the Keplerian orbital velocity. Beyond this corotation limit (CoRoL), a hot planetary body forms a structure, which we name a synestia, with a corotating inner region connected to a disk-like outer region. By analyzing calculations of giant impacts and models of planet formation, we show that typical rocky planets are substantially vaporized multiple times during accretion. For the expected angular momentum of growing planets, a large fraction of post-impact bodies will exceed the CoRoL and form synestias. The common occurrence of hot, rotating states during accretion has major implications for planet formation and the properties of the final planets. In particular, the structure of post-impact bodies influences the physical processes that control accretion, core formation and internal evolution. Synestias also lead to new mechanisms for satellite formation. Finally, the wide variety of possible structures for terrestrial bodies also expands the mass-radius range for rocky exoplanets.

arXiv commentMain text: 31 pages, 15 figures. Supporting information: 15 pages, 8 figures

References in corpus (38)

• The cosmological simulation code GADGET-2
• A low mass for Mars from Jupiter's early gas-driven migration
• Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data
• Mass-Radius Relationships for Solid Exoplanets
• Most 1.6 Earth-Radius Planets are not Rocky
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• Internal Structure of Massive Terrestrial Planets
• Building the Terrestrial Planets: Constrained Accretion in the Inner Solar System
• False positive probabilties for all Kepler Objects of Interest: 1284 newly validated planets and 428 likely false positives
• Mass-Radius Relation for Rocky Planets based on PREM
• Accretion and differentiation of the terrestrial planets with implications for the compositions of early-formed Solar System bodies and accretion of water
• Collisions between Gravity-Dominated Bodies: 2. The Diversity of Impact Outcomes during the End Stage of Planet Formation
• Collisions Between Gravity-Dominated Bodies: 1. Outcome Regimes and Scaling Laws
• Equilibration in the Aftermath of the Lunar-Forming Giant Impact
• Formation of the Terrestrial Planets from a Narrow Annulus
• A map of the large day-night temperature gradient of a super-Earth exoplanet
• A Detailed Model Grid for Solid Planets from 0.1 through 100 Earth Masses
• Melting and Mixing States of the Earth's Mantle after the Moon-Forming Impact
• Atmospheric Mass Loss During Planet Formation: The Importance of Planetesimal Impacts
• Growing the terrestrial planets from the gradual accumulation of sub-meter sized objects
• Transits and Occultations of an Earth-Sized Planet in an 8.5-Hour Orbit
• Evidence for multiple magma ocean outgassing and atmospheric loss episodes from mantle noble gases
• Mass-radius relationships for exoplanets
• Formation of Terrestrial Planets from Protoplanets under a Realistic Accretion Condition
• Scaling the Earth: A Sensitivity Analysis of Terrestrial Exoplanetary Interior Models
• Debris from terrestrial planet formation: the Moon-forming collision
• Collisional Stripping and Disruption of Super-Earths
• Tidal evolution of the Moon from a high-obliquity, high-angular-momentum Earth
• The Frequency of Giant impacts on Earth-like Worlds
• Concentric Maclaurin spheroid models of rotating liquid planets
• Lunar accretion from a Roche-interior fluid disk
• Investigation of the Initial State of the Moon-Forming Disk: Bridging SPH Simulations and Hydrostatic Models
• Compositional evolution during rocky protoplanet accretion
• Decaying shock studies of phase transitions in MgOSiO2 systems: implications for the Super-Earths interiors
• High-temperature miscibility of iron and rock during terrestrial planet formation
• Rocky Planet Formation: Quick and Neat
• Accretion of the Moon from non-canonical disks
• Formation and Evolution of Binary Asteroids

Cited by in corpus (34)

• The origin of the Moon within a terrestrial synestia
• The timeline of the Lunar bombardment - revisited
• Thermodynamics of Element Volatility and its Application to Planetary Processes
• A new perspective on interiors of ice-rich planets: Ice-rock mixture instead of ice on top of rock
• The Shock Physics of Giant Impacts: Key Requirements for the Equations of State
• Collisional stripping of planetary crusts
• Silicate Melting and Vaporization during Rocky Planet Formation
• Extreme Debris Disk Variability -- Exploring the Diverse Outcomes of Large Asteroid Impacts During the Era of Terrestrial Planet Formation
• Atmosphere loss in planet-planet collisions
• Giant planet effects on terrestrial planet formation and system architecture
• Primordial Earth mantle heterogeneity caused by the Moon-forming giant impact
• The energy budget and figure of Earth during recovery from the Moon-forming giant impact
• Modeling a Transient Secondary Paleo-Lunar Atmosphere: 3-D Simulations and Analysis
• Employing magma ocean crystallization models to constrain structure and composition of the lunar interior
• Rotating convective turbulence in moderate to high Prandtl number fluids
• The effect of pre-impact spin on the Moon-forming collision
• The role of multiple giant impacts in the formation of the Earth-Moon system
• The three regimes of atmospheric evaporation for super-Earths and sub-Neptunes
• The Exosphere as a Boundary: Origin and Evolution of Airless Bodies in the Inner Solar System and Beyond Including Planets with Silicate Atmospheres
• Explaining Mercury via a single giant impact is highly unlikely
• Giant impacts stochastically change the internal pressures of terrestrial planets
• The Cosmic Shoreline Revisited: A Metric for Atmospheric Retention Informed by Hydrodynamic Escape
• Mercury's formation within the Early Instability Scenario
• Analytical Model for the Tidal Evolution of the Evection Resonance and the Timing of Resonance Escape
• Composition, Structure and Origin of the Moon
• EXONEST: The Bayesian Exoplanetary Explorer
• Collisional fragmentation and bulk composition tracking in REBOUND
• The distribution of impactor core material during large impacts on Earth-like planets
• Interior potential of a toroidal shell from pole values
• Rigidly rotating, incompressible spheroid-ring systems: new bifurcations, critical rotations and degenerate states
• The possibility of a giant impact on Venus
• Re-accretion of Giant Impact Ejecta Can Drive Significant Atmospheric Erosion on Terrestrial Planets
• Special cases : moons, rings, comets, trojans
• The energy budgets of giant impacts