Oral Presentation

Rapid Rocky Planetesimal Formation Driven by Dust and Temperature Coevolution in Early Inner Disks

Author(s): Ryo Kato (Science Tokyo) Takahiro Ueda (NAOJ) Satoshi Okuzumi (Science Tokyo)

Presenter: Ryo Kato (Institute Science of Tokyo)

The prevalence of close-in super-Earths raises the fundamental question of when and how planetesimals form in the innermost regions of protoplanetary disks. One promising scenario is dust accumulation at a pressure bump near the magnetorotational instability (MRI) activation front (e.g., Kretke et al. 2009; Ueda et al. 2019). However, thermal instability in viscously heated disks may make this front and its pressure bump unsteady (e.g., Cecil & Flock 2024). This may be particularly important in young disks, where high accretion rates are expected (Takakuwa et al. 2024).
In this study, we investigate whether planetesimals can form in such thermally unstable inner regions of young disks by considering the coevolution of dust and disk temperature. To this end, we simultaneously calculate the evolution of gas and dust surface densities, dust growth, and the thermal evolution of the disk (Kato, Ueda, & Okuzumi, under revision; arXiv:2604.27581).
Our results show that cyclic MRI activation and deactivation produce a local dust enhancement (dust bump). Formed near the outer edge of the MRI-active region, this bump traps heat generated by viscous dissipation, raises the local temperature, and creates a pressure bump that further promotes dust accumulation (Kato et al. 2025). As the bump migrates inward while accumulating dust, planetesimals form successively from larger to smaller orbital radii.
For gas accretion rates ranging from 10^-6 to 10^-8 solar masses per year, planetesimals form in annular regions around 1 au, with belt widths and locations varying among the models. In all cases, the total planetesimal mass reaches a few Earth masses within a few thousand years. These results suggest that the initial planetesimal distribution and mass budget shaping close-in super-Earth systems can be established during a phase much shorter than the disk lifetime.