# Influence of grain growth on the thermal structure of protoplanetary discs

**Authors:** Sofia Savvidou, Bertram Bitsch, Michiel Lambrechts  
**arXiv:** [2005.14097](https://arxiv.org/abs/2005.14097)  
**Date:** 2020-05-28  
**Summary page:** https://www.summarizepaper.com/en/paper/2005.14097v1/

## Key points

- The study investigates the impact of dust grain size distribution on the thermal structure and migration rates in protoplanetary discs.
- 2D hydrodynamical simulations were performed, taking into account particle size, composition, and abundance.
- Single grain sizes lead to inaccurate calculations of the thermal structure of discs because the grain size dominating opacity increases with orbital radius.
- Both multi-grain size distributions give similar results for thermal structure but less steep opacity gradients resulting in less steep aspect ratio gradients compared to discs with only micrometer-sized dust.
- Discs with a grain size distribution embedded planets experience lower migration rates compared to those with only micrometer-sized dust.
- Water iceline position depends on alpha-viscosity, initial gas surface density at 1 AU, and dust-to-gas ratio.
- $r_{ice} \propto \alpha^{0.61} \Sigma_{g,0}^{0.8} f_{DG}^{0.37}$ independently of the distribution used.
- Including feedback loops between grain growth, opacities and disc thermodynamics allows for more self-consistent simulations when studying accretion disks and planet formation processes.

## Summary

In the study "Influence of grain growth on the thermal structure of protoplanetary discs," Sofia Savvidou, Bertram Bitsch, and Michiel Lambrechts investigate the impact of dust grain size distribution on the thermal structure and migration rates in protoplanetary discs. The authors perform 2D hydrodynamical simulations of protoplanetary discs where they self-consistently calculate the opacity for the dust population, taking into account particle size, composition, and abundance. They compare simulations using single grain sizes to two different multi-grain size distributions at different levels of turbulence strengths parameterized through the $\alpha$-viscosity and different gas surface densities. The authors find that assuming a single dust size leads to inaccurate calculations of the thermal structure of discs because the grain size dominating opacity increases with orbital radius. Overall, both grain size distributions give similar results for thermal structure; however, they find that both distributions give less steep opacity gradients resulting in less steep aspect ratio gradients compared to discs with only micrometer-sized dust. Additionally, in discs with a grain size distribution embedded planets experience lower migration rates compared to those with only micrometer-sized dust. The authors also investigate how water iceline position depends on alpha-viscosity, initial gas surface density at 1 AU, and dust-to-gas ratio. They find $r_{ice} \propto \alpha^{0.61} \Sigma_{g,0}^{0.8} f_{DG}^{0.37}$ independently of the distribution used. Overall, this study highlights how including feedback loops between grain growth, opacities and disc thermodynamics allows for more self-consistent simulations when studying accretion disks and planet formation processes.