Transport, destruction and growth of pebbles in the gas envelope of a protoplanet

Abstract

We analyse the size evolution of pebbles accreted into the gaseous envelope of a protoplanet growing in a protoplanetary disc, taking into account collisions driven by the relative sedimentation speed as well as the convective gas motion. Using a simple estimate of the convective gas speed based on the pebble accretion luminosity, we find that the speed of the convective gas is higher than the sedimentation speed for all particles smaller than 1 mm. This implies that both pebbles and pebble fragments are strongly affected by the convective gas motion and will be transported by large-scale convection cells both towards and away from the protoplanet's surface. We present a simple scheme for evolving the characteristic size of the pebbles, taking into account the effects of erosion, mass transfer and fragmentation. Including the downwards motion of convective cells for the transport of pebbles with an initial radius of 1 millimeter, we find pebble sizes between 100 microns and 1 millimeter near the surface of the protoplanet. These sizes are generally amenable to accretion at the base of the convection flow. Small protoplanets far from the star (>30 AU) nevertheless erode their pebbles to sizes below 10 microns; future hydrodynamical simulations will be needed to determine whether such small fragments can detach from the convection flow and become accreted by the protoplanet.

arXiv commentAccepted for publication in The Astrophysical Journal

References in corpus (30)

• Using FU Orionis Outbursts to Constrain Self-Regulated Protostellar Disk Models
• Rapid growth of gas-giant cores by pebble accretion
• The effect of gas drag on the growth of protoplanets -- Analytical expressions for the accretion of small bodies in laminar disks
• The outcome of protoplanetary dust growth: pebbles, boulders, or planetesimals? I. Mapping the zoo of laboratory collision experiments
• Closed-form expressions for particle relative velocities induced by turbulence
• Forming Planetesimals in Solar and Extrasolar Nebulae
• Atmospheres of protoplanetary cores: critical mass for nucleated instability
• The great dichotomy of the Solar System: small terrestrial embryos and massive giant planet cores
• Formation of planetary systems by pebble accretion and migration: How the radial pebble flux determines a terrestrial-planet or super-Earth growth mode
• Why do protoplanetary disks appear not massive enough to form the known exoplanet population?
• On the Minimum Core Mass for Giant Planet Formation at Wide Separations
• Contacts of Water Ice in Protoplanetary Disks - Laboratory Experiments
• Reduced gas accretion on super-Earths and ice giants
• How planetary growth outperforms migration
• How cores grow by pebble accretion I. Direct core growth
• Sticking Properties of Silicates in Planetesimal Formation Revisited
• Suppression of atmospheric recycling of planets embedded in a protoplanetary disc by buoyancy barrier
• Erosion of dust aggregates
• How planets grow by pebble accretion II: Analytical calculations on the evolution of polluted envelopes
• Pebble dynamics and accretion onto rocky planets. I. Adiabatic and convective models
• The maximum mass of planetary embryos formed in core-accretion models
• The steady-state flow pattern past gravitating bodies
• Exploring the conditions for forming cold gas giants through planetesimal accretion
• The role of pebble fragmentation in planetesimal formation I. Experimental study
• The physics of protoplanetesimal dust agglomerates. X. High-velocity collisions between small and large dust agglomerates as growth barrier
• Pebble dynamics and accretion onto rocky planets. II. Radiative models
• Spontaneous concentrations of solids through two-way drag forces between gas and sedimenting particles
• Steamworlds: atmospheric structure and critical mass of planets accreting icy pebbles
• Limits on Protoplanet Growth by Accretion of Small Solids
• Observation of aerodynamic instability in the flow of a particle stream in a dilute gas

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• Sublimation of refractory minerals in the gas envelopes of accreting rocky planets
• The cosmochemistry of planetary systems
• Prograde spin-up during gravitational collapse
• Dust processing in protoplanetary envelopes as the origin of hot minerals in comets
• Explosive instability of dust settling in a protoplanetary disc
• Interior dynamics of envelopes around disk-embedded planets