Formation of multiple-planet systems in resonant chains around M dwarfs

TL;DR

This paper models the formation of multiple-planet systems in resonant chains around low-mass M dwarf stars, highlighting the importance of protoplanet appearance timescales in determining system architecture.

Contribution

It introduces a time-evolution model for planet formation via pebble accretion around low-mass stars, emphasizing the role of protoplanet appearance timing in resonant chain formation.

Findings

Fewer planets form with longer protoplanet appearance timescales.

Stable resonant chains depend on stellar mass and disk size.

Protoplanet appearance timescale is a key parameter in system formation.

Abstract

Recent observations have revealed the existence of multiple-planet systems composed of Earth-mass planets around late M dwarfs. Most of their orbits are close to commensurabilities, which suggests that planets were commonly trapped in resonant chains in their formation around low-mass stars. We investigate the formation of multiple-planet systems in resonant chains around low-mass stars. A time-evolution model of the multiple-planet formation via pebble accretion in the early phase of the disk evolution is constructed based on the formation model for the TRAPPIST-1 system by Ormel et al. (2017). Our simulations show that knowing the protoplanet appearance timescale is important for determining the number of planets and their trapped resonances: as the protoplanet appearance timescale increases, fewer planets are formed, which are trapped in more widely separated resonances. We find that there is a range of the protoplanet appearance timescale for forming the stable multiple-planet systems in resonant chains. This range depends on the stellar mass and disk size. We suggest that the protoplanet appearance timescale is a key parameter for studying the formation of multiple-planet systems with planets in resonant chains around low-mass stars. The composition of the planets in our model is also discussed.