Planet formation and disk mass dependence in a pebble-driven scenario for low mass stars

TL;DR

This study develops a population synthesis model based on pebble accretion to analyze how disk mass influences planet formation around low-mass stars, revealing that observed low disk masses may be underestimated or insufficient for forming observed planetary systems.

Contribution

It introduces a new population synthesis code for pebble-driven planet formation around low-mass stars, exploring the impact of initial disk mass on planetary system outcomes.

Findings

Compact resonant systems are common around M-dwarfs with sufficiently massive disks.

Minimum disk mass for Mars-like planet formation is about 2×10⁻³ M☉.

Observed disk masses may be underestimated or planets rapidly deplete disk material.

Abstract

Measured disk masses seem to be too low to form the observed population of planetary systems. In this context, we develop a population synthesis code in the pebble accretion scenario, to analyse the disk mass dependence on planet formation around low mass stars. We base our model on the analytical sequential model presented in Ormel et al. 2017 and analyse the populations resulting from varying initial disk mass distributions. Starting out with seeds the mass of Ceres near the ice-line formed by streaming instability, we grow the planets using the Pebble Accretion process and migrate them inwards using Type-I migration. The next planets are formed sequentially after the previous planet crosses the ice-line. We explore different initial distributions of disk masses to show the dependence of this parameter with the final planetary population. Our results show that compact close-in resonant systems can be pretty common around M-dwarfs between $0.09-0.2$ $M_{\odot}$ only when the disks considered are more massive than what is being observed by sub-mm disk surveys. The minimum disk mass to form a Mars-like planet is found to be about $2 \times 10^{-3}$ $M_{\odot}$. Small variation in the disk mass distribution also manifest in the simulated planet distribution. The paradox of disk masses might be caused by an underestimation of the disk masses in observations, by a rapid depletion of mass in disks by planets growing within a million years or by deficiencies in our current planet formation picture.