The Terrestrial Planet Formation around M Dwarfs: In-situ, Inward Migration or Reversed Migration

TL;DR

This study uses N-body simulations to compare in-situ, inward, and reversed migration models for terrestrial planet formation around M dwarfs, finding reversed migration best matches observed systems.

Contribution

It introduces comprehensive simulation comparisons of different migration scenarios, highlighting reversed migration as the most consistent with observations.

Findings

Reversed migration produces the most realistic planetary systems.

In-situ formation results in an average of 7.77 planets per system.

Migration scenarios facilitate water delivery to inner planets.

Abstract

Terrestrial planets are commonly observed to orbit M dwarfs with close-in trajectories. In this work, we extensively perform N-body simulations of planetesimal accretion with three models of in-situ, inward migration and reversed migration to explore terrestrial formation in tightly compact systems of M dwarfs. In the simulations, the solid disks are assumed to be 0.01\% of the masses of host stars and spread from 0.01 to 0.5 AU with the surface density profile scaling with $r^{-k}$ according to the observations. Our results show that in-situ scenario may produce $7.77^{+3.23}_{-3.77}$ terrestrial planets with an average mass of $1.23^{+4.01}_{-0.93} \ M_{\oplus}$ around M dwarfs. The number of planets tends to increase as the disk slope is steeper or with a larger stellar mass. Moreover, we show that $2.55^{+1.45}_{-1.55}$ planets with mass of $3.76^{+8.77}_{-3.46} \ M_{\oplus}$ are formed in the systems via inward migration, while $2.85^{+1.15}_{-0.85}$ planets with $3.01^{+13.77}_{-2.71} \ M_{\oplus}$ are yielded under reversed migration. Migration scenarios can also deliver plentiful water from the exterior of ice line to the interior due to more efficient accretion. The simulation outcomes of reversed migration model produce the best matching with observations, being suggestive of a likely mechanism for planetary formation around M dwarfs.