Dynamical Constraints on Mercury's Collisional Origin

Abstract

Of the solar system's four terrestrial planets, the origin of Mercury is perhaps the most mysterious. Modern numerical simulations designed to model the dynamics of terrestrial planet formation systematically fail to replicate Mercury; which possesses just 5% the mass of Earth and the highest orbital eccentricity and inclination among the planets. However, Mercury's large iron-rich core and low volatile inventory stand out among the inner planets, and seem to imply a violent collisional origin. Because most algorithms used for simulating terrestrial accretion do not consider the effects of collisional fragmentation, it has been difficult to test these collisional hypotheses within the larger context of planet formation. Here, we analyze a large suite of terrestrial accretion models that account for the fragmentation of colliding bodies. We find that planets with core mass fractions boosted as a result of repeated hit-and-run collisions are produced in 90% of our simulations. While many of these planets are similar to Mercury in mass, they rarely lie on Mercury-like orbits. Furthermore, we perform an additional batch of simulations designed to specifically test the single giant impact origin scenario. We find less than a 1% probability of simultaneously replicating the Mercury-Venus dynamical spacing and the terrestrial system's degree of orbital excitation after such an event. While dynamical models have made great strides in understanding Mars' low mass, their inability to form accurate Mercury analogs remains a glaring problem.

11 pages, 7 figures, 2 tables, accepted for publication in AJ

References in corpus (54)

• Disk Frequencies and Lifetimes in Young Clusters
• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• A low mass for Mars from Jupiter's early gas-driven migration
• REBOUND: An open-source multi-purpose N-body code for collisional dynamics
• A simple model for the evolution of the dust population in protoplanetary disks
• WHFast: A fast and unbiased implementation of a symplectic Wisdom-Holman integrator for long term gravitational simulations
• Making other Earths: Dynamical Simulations of Terrestrial Planet Formation and Water Delivery
• Building the Terrestrial Planets: Constrained Accretion in the Inner Solar System
• 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
• High-resolution simulations of the final assembly of Earth-like planets 1: terrestrial accretion and dynamics
• Statistical Study of the Early Solar System's Instability with 4, 5 and 6 Giant Planets
• On the orbital evolution and growth of protoplanets embedded in a gaseous disc
• Formation of the Terrestrial Planets from a Narrow Annulus
• Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn's rapid gas accretion
• The Exoplanet Population Observation Simulator. I - The Inner Edges of Planetary Systems
• Close-in planetesimal formation by pile-up of drifting pebbles
• All Six Planets Known to Orbit Kepler-11 Have Low Densities
• Mars' Growth Stunted by an Early Giant Planet Instability
• Young Solar System's Fifth Giant Planet?
• Merging Criteria for Giant Impacts of Protoplanets
• On the evolution of eccentric and inclined protoplanets embedded in protoplanetary disks
• Multiple Impact Origin for the Moon
• Jupiter's Decisive Role in the Inner Solar System's Early Evolution
• The Frequency of Giant impacts on Earth-like Worlds
• Advances in exoplanet science from Kepler
• The early instability scenario: terrestrial planet formation during the giant planet instability, and the effect of collisional fragmentation
• The GENGA Code: Gravitational Encounters in N-body simulations with GPU Acceleration
• Theory of Secular Chaos and Mercury's Orbit
• A primordial origin for the composition similarity between the Earth and the Moon
• Terrestrial Planet Formation Constrained by Mars and the Structure of the Asteroid Belt
• Formation, stratification, and mixing of the cores of Earth and Venus
• The Feeding Zones of Terrestrial Planets and Insights into Moon Formation
• Compositional evolution during rocky protoplanet accretion
• Terrestrial Planet Formation in a protoplanetary disk with a local mass depletion: A successful scenario for the formation of Mars
• Rapid Formation of Icy Super-Earths and the Cores of Gas Giant Planets
• The Fragility of the Terrestrial Planets During a Giant Planet Instability
• Constraining the giant planets' initial configuration from their evolution: implications for the timing of the planetary instability
• A Collisional Origin to Earth's Non-chondritic Composition?
• Forming Mercury by Giant Impacts
• Dynamical Shakeup of Planetary Systems II. N-body simulations of Solar System terrestrial planet formation induced by secular resonance sweeping
• Terrestrial Planet Formation from an Annulus
• Excitation and depletion of the asteroid belt in the early instability scenario
• Terrestrial Planet Formation During the Migration and Resonance Crossings of the Giant Planets
• Numerically Predicted Indirect Signatures of Terrestrial Planet Formation
• Terrestrial planet formation: Dynamical shake-up and the low mass of Mars
• Constraints on the pre-impact orbits of Solar System giant impactors
• Jumping Jupiter can explain Mercury's orbit
• Did Jupiter's core form in the innermost parts of the Sun's protoplanetary disk?
• Terrestrial Planet Formation: Constraining the Formation of Mercury
• Dynamical Evolution of the Earth-Moon Progenitors - Whence Theia?
• The role of multiple giant impacts in the formation of the Earth-Moon system
• Collisional Fragmentation is Not a Barrier to Close-in Planet Formation
• Prevalance of Chaos in Planetary Systems Formed Through Embryo Accretion

Cited by in corpus (22)

• Chemical Fingerprints of Formation in Rocky Super-Earths' Data
• Solar System Physics for Exoplanet Research
• The Role of Early Giant Planet Instability in the Terrestrial Planet Formation
• Constraining the Formation of the Four Terrestrial Planets in the Solar System
• The terrestrial planet formation paradox inferred from high-resolution N-body simulations
• Terrestrial planet formation from a ring
• Dynamical avenues for Mercury's origin I: The lone survivor of a primordial generation of short-period proto-planets
• Habitable planet formation around low-mass stars: Rapid accretion, rapid debris removal and the essential contribution of external giants
• Dynamical avenues for Mercury's origin II: in-situ formation in the inner terrestrial disk
• The early instability scenario: Mars' mass explained by Jupiter's orbit
• 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
• Modification of the composition and density of Mercury from late accretion
• Terrestrial planet and asteroid belt formation by Jupiter-Saturn chaotic excitation
• Mercury's formation within the Early Instability Scenario
• Building Terrestrial Planets: Why results of perfect-merging simulations are not quantitatively reliable approximations to accurate modeling of terrestrial planet formation
• Extreme close encounters between proto-Mercury and proto-Venus in terrestrial planet formation
• Can narrow disks in the inner solar system explain the four terrestrial planets?
• Hypothetical hyperbolic encounters between Venus and proto-Mercury that partially \ stripped away proto-Mercury's mantle
• Formation of the four terrestrial planets in the Jupiter-Saturn chaotic excitation scenario: fundamental properties and water delivery
• Origins of Mercury's Big Heart of Iron: Exploring Pathways to Form High Core Mass Fraction (CMF) Planets via N-body Simulations
• Water worlds in N-body simulations with fragmentation in systems without gaseous giants