Heavy-metal Jupiters by major mergers: metallicity vs. mass for giant planets

Abstract

Some Jupiter-mass exoplanets contain $\sim$$100M_{\oplus }$ of metals, well above the $\sim$$10M_{\oplus }$ typically needed in a solid core to trigger giant planet formation by runaway gas accretion. We demonstrate that such `heavy-metal Jupiters' can result from planetary mergers near $\sim$10 au. Multiple cores accreting gas at runaway rates gravitationally perturb one another onto crossing orbits such that the average merger rate equals the gas accretion rate. Concurrent mergers and gas accretion implies the core mass scales with the total planet mass as $M_{\mathrm{core}}\propto M^{1/5}$ - heavier planets harbour heavier cores, in agreement with the observed mass-metallicity relation. While the average gas giant merges about once to double its core, others may merge multiple times, as merger trees grow chaotically. We show that the dispersion of outcomes inherent in mergers can reproduce the large scatter in observed planet metallicities, assuming $3-30M_{\oplus }$ pre-runaway cores. Mergers potentially correlate metallicity, eccentricity, and spin.

Submitted to MNRAS

References in corpus (18)

• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• Post-Oligarchic Evolution of Protoplanetary Embryos and the Stability of Planetary Systems
• Formation of close in Super-Earths \& Mini-Neptunes: Required Disk Masses \& Their Implications
• Minimum Core Masses for Giant Planet Formation With Realistic Equations of State and Opacities
• On the Origin of HD149026b
• The Formation of Jupiter's Diluted Core by a Giant Impact
• Four Sub-Saturns with Dissimilar Densities: Windows into Planetary Cores and Envelopes
• The origin of the high metallicity of close-in giant exoplanets: Combined effect of the resonant and aerodynamic shepherding
• Constraining the Oblateness of Kepler Planets
• Identifying and Analysing Protostellar Disc Fragments in Smoothed Particle Hydrodynamics Simulations
• Dynamics and Accretion of Planetesimals
• The End of Runaway: How Gap Opening Limits the Final Masses of Gas Giants
• Breaking the centrifugal barrier to giant planet contraction by magnetic disc braking
• Embryo impacts and gas giant mergers II: Diversity of Hot Jupiters' internal structure
• Fundamental limits from chaos on instability time predictions in compact planetary systems
• The Endgame of Gas Giant Formation: Accretion Luminosity and Contraction Post-Runaway
• Planetary Spin and Obliquity from Mergers
• TW Hya: an old protoplanetary disc revived by its planet

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• Synthetic Evolution Tracks of Giant Planets
• Planet Engulfment Signatures in Twin Stars
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• Towards a new era in giant exoplanet characterisation
• Revising the Giant Planet Mass-Metallicity Relation: Deciphering the Formation Sequence of Giant Planets
• Formation of giant planets with large metal masses and metal fractions via giant impacts in a rapidly dissipating disk
• The origin of the high metallicity of close-in giant exoplanets II The nature of the sweet spot for accretion
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• Solid Accretion onto Neptune-Mass Planets I: In-Situ Accretion and Constraints from the metallicity of Uranus and Neptune
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• Interpreting the atmospheric composition of exoplanets: sensitivity to planet formation assumptions
• Direct Images of CO2 Absorption in the Atmosphere of a Super-Jupiter: Enhanced Metallicity Suggestive of Formation in a Disk
• A sub-Saturn Mass-Radius Desert for Planets with Equilibrium Temperature Less than 600 K
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