Dust-Gas Coupling in Turbulence- and MHD Wind-Driven Protoplanetary Disks: Implications for Rocky Planet Formation

Abstract

The degree of coupling between dust particles and their surrounding gas in protoplanetary disks is quantified by the dimensionless Stokes number. The Stokes number (St) governs particle size and spatial distributions, in turn establishing the dominant mode of planetary accretion in different disk regions. In this paper, we model the characteristic St of particles across time in disks evolving under both turbulent viscosity and magnetohydrodynamic (MHD) disk winds. In both turbulence- and wind-dominated disks, we find that collisional fragmentation is the limiting mechanism of particle growth, and the water-ice sublimation line constitutes a critical transition point between dust settling, drift, and size regimes. The St dichotomy across the ice-line translates to distinct planet formation pathways between the inner and outer disk. While pebble accretion proceeds slowly for rocky embryos within the ice-line (across most of parameter space), it does so rapidly for volatile-rich embryos beyond it, allowing for the growth of giant planet cores before disk dissipation. Through simulations of rocky planet growth, we evaluate the competition between pebble accretion and classical pairwise collisions between planetesimals. We conclude that the dominance of pebble accretion can only be realized in disks that are driven by MHD winds, slow-evolving, and devoid of pressure maxima that may concentrate solids and give rise of planetesimal rings. Such disks are extremely quiescent, with Shakura-Sunyaev turbulence parameters ${\alpha }_{\nu }\sim 10^{-4}$. We conclude that for most of parameter space corresponding to values of ${\alpha }_{\nu }$ reflected in observations of protoplanetary disks ($\gtrsim 10^{-4}$), pairwise collisions constitute the dominant pathway of rocky planet accretion. Our results are discussed in the context of super-Earth origins and Earth's accretion history.

Presented at the 2024 Lunar and Planetary Science Conference

References in corpus (26)

• Protoplanetary Disk Structures in Ophiuchus
• Closed-form expressions for particle relative velocities induced by turbulence
• Separating gas-giant and ice-giant planets by halting pebble accretion
• The stickiness of micrometer-sized water-ice particles
• Dust size distributions in coagulation/fragmentation equilibrium: Numerical solutions and analytical fits
• Initial mass function of planetesimals formed by the streaming instability
• Contacts of Water Ice in Protoplanetary Disks - Laboratory Experiments
• Formation of planetary systems by pebble accretion and migration: Growth of gas giants
• Full Numerical Simulations of Catastrophic Small Body Collisions
• A perspective from extinct radionuclides on a Young Stellar Object: The Sun and its accretion disk
• Contemporary formation of early solar system planetesimals at two distinct radial locations
• Terrestrial planet formation from lost inner solar system material
• Planetesimal rings as the cause of the Solar System's planetary architecture
• Turbulence sets the length scale for planetesimal formation: Local 2D simulations of streaming instability and planetesimal formation
• Empirical constraints on turbulence in proto-planetary discs
• A reassessment of the in situ formation of close-in super-Earths
• Formation of Giant Planet Satellites
• Rocky super-Earths or waterworlds: the interplay of planet migration, pebble accretion and disc evolution
• Planetesimal Population Synthesis: Pebble Flux Regulated Planetesimal Formation
• Planet formation and migration near the silicate sublimation front in protoplanetary disks
• Growing and Trapping Pebbles with Fragile Collisions of Particles in Protoplanetary Disks
• Setting the Stage for Planet Formation: Measurements and Implications of the Fundamental Disk Properties
• Bayesian Inference on the Isotopic Building Blocks of Mars and Earth
• Stochastic accretion of the Earth
• Drifting inwards in protoplanetary discs II: The effect of water on sticking properties at increasing temperatures
• Lifetime of the Outer Solar System Nebula From Carbonaceous Chondrites

Cited by in corpus (2)

• Infall and Disk Processes - the Message from Meteorites
• Early Solar System Turbulence Constrained by High Oxidation States of the Oldest Non-Carbonaceous Planetesimals