Global Modeling of Nebulae With Particle Growth, Drift, and Evaporation Fronts. I. Methodology and Typical Results

Abstract

We model particle growth in a turbulent, viscously evolving protoplanetary nebula, incorporating sticking, bouncing, fragmentation, and mass transfer at high speeds. We treat small particles using a moments method and large particles using a traditional histogram binning, including a probability distribution function of collisional velocities. The fragmentation strength of the particles depends on their composition (icy aggregates are stronger than silicate aggregates). The particle opacity, which controls the nebula thermal structure, evolves as particles grow and mass redistributes. While growing, particles drift radially due to nebula headwind drag. Particles of different compositions evaporate at "evaporation fronts" (EFs) where the midplane temperature exceeds their respective evaporation temperatures. We track the vapor and solid phases of each component, accounting for advection and radial and vertical diffusion. We present characteristic results in evolutions lasting 2 × 10 5 years. In general, (a) mass is transferred from the outer to inner nebula in significant amounts, creating radial concentrations of solids at EFs; (b) particle sizes are limited by a combination of fragmentation, bouncing, and drift; (c) "lucky" large particles never represent a significant amount of mass; and (d) restricted radial zones just outside each EF become compositionally enriched in the associated volatiles. We point out implications for mm-submm SEDs and inference of nebula mass, radial banding, the role of opacity on new mechanisms for generating turbulence, enrichment of meteorites in heavy oxygen isotopes, variable and nonsolar redox conditions, primary accretion of silicate and icy planetesimals, and the makeup of Jupiter's core.

Local growth of dust- and ice-mixed aggregates as cometary building blocks in the solar nebula

“…They found that while erosion-limited growth of icy aggregates can easily produce aggregates with the right Stokes number for streaming instability, the mass loading in the disk midplane is too low in large parts of the disk. Estrada et al (2016) performed global simulations of dust growth in protoplanetary disks. While they took detailed physics into account, such as condensation fronts and a collision model comparable to ours, porosity was not considered.…”

Linear growth of streaming instability in pressure bumps

“…On the other hand, local pressure maxima may be created in the disc at some locations by internal processes (e.g. Ruge et al 2016;Estrada et al 2016;Béthune et al 2016;Gonzalez et al 2017). These pressure bumps are privileged locations for planetesimal formation since they concentrate dust (e.g.…”

Making Terrestrial Planets: High Temperatures, FU Orionis Outbursts, Earth, and Planetary System Architectures

“…Significantly, most other mechanisms that have been proposed to bypass those barriers that have not been ruled out by numerical study (Estrada et al 2016) are inconsistent with the volatile abundances of the terrestrial planets in the Solar System (Flynn et al 2013;Marty et al 2013). This thermal processing seems likely to take two forms depending on the host disk dynamics, and those forms would set the planetary system architecture in an in situ planet formation scenario.…”

“…In a recent epic endeavor Estrada et al (2016) verified that the problem persists even taking into account lucky grains (Windmark et al 2012;Garaud et al 2013). In this section we quickly sketch how large modifications to our understanding would be required to allow dry silicates to form planetesimals.…”

“…The bouncing barrier and its consequences has been explored numerically (e.g. Zsom et al 2010;Windmark et al 2012;Garaud et al 2013;Estrada et al 2016), and found to prohibit grain growth to SI triggering dust sizes.…”