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

Abstract

ABSTRACT Measured disc 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 disc mass dependence on planet formation around low-mass stars. We base our model on the analytical sequential model presented by Ormel, Liu, and Schoonenberg and analyse the populations resulting from varying initial disc mass distributions. Starting out with seeds the mass of Ceres formed by streaming instability inside the ice-line, 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 disc 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 and 0.2 M⊙ only when the discs considered are more massive than what is being observed by sub-mm disc surveys. The minimum disc mass to form a Mars-like planet is found to be about 2 × 10−3 M⊙. Small variations in the disc mass distribution also manifest in the simulated planet distribution. The paradox of disc masses might be caused by an underestimation of the disc masses in observations, by a rapid depletion of mass in discs by planets growing within 1 million years, or by deficiencies in our current planet formation picture.