Effects of Chemistry on Vertical Dust Motion in Early Protoplanetary Disks

TL;DR

This paper explores how chemical processes like evaporation and condensation influence dust settling in early protoplanetary disks, revealing complex behaviors that affect planetesimal composition.

Contribution

It introduces a 1-D model incorporating chemical effects on dust dynamics, highlighting the formation of a condensation front and its impact on dust evolution.

Findings

Evaporation forms a condensation front with temperature gradients.

Refractory elements show contrasting settling behaviors.

Silicate evaporation persists longer than previously estimated.

Abstract

We propose the possibility of a new phenomenon affecting the settling of dust grains at the terrestrial region in early protoplanetary disks. Sinking dust grains evaporate in a hot inner region during the early stage of disk evolution, and the effects of condensation and evaporation on vertical dust settling can be significant. A 1-D dust settling model considering both physical and chemical aspects is presented in this paper. Modeling results show that dust grains evaporate as they descend into the hotter interior and form a "condensation front," above which dust-composing major elements, Mg, Si, and Fe, accumulate, creating a large temperature gradient. Repeated evaporation at the front inhibits grain growth, and small grain sizes elevate the opacity away from the mid-plane. Self-consistent calculations including radiative heat transfer and condensation theory suggest that the mid-disk temperature could be high enough for silicates to remain evaporated longer than previous estimates. The formation of a condensation front leads to contrasting settling behaviors between highly refractory elements, such as Al and Ca, and moderately refractory elements, such as Mg, Si, and Fe, suggesting that elemental abundance in planetesimals may not be a simple function of volatility.