Accretion of Terrestrial Planets from Oligarchs in a Turbulent Disk

TL;DR

This study uses N-body simulations to explore how turbulence in protoplanetary disks influences the final formation of terrestrial planets, showing turbulence can lead to fewer, Earth-mass planets with low eccentricities.

Contribution

It introduces a model incorporating disk turbulence effects into planet formation simulations, revealing turbulence's role in planet number and orbital characteristics.

Findings

Turbulence delays planetary isolation, promoting more coagulation.

Final planet count decreases with increased turbulence strength.

Earth-mass planets with low eccentricities can form under various turbulence conditions.

Abstract

We have investigated the final accretion stage of terrestrial planets from Mars-mass protoplanets that formed through oligarchic growth in a disk comparable to the minimum mass solar nebula (MMSN), through N-body simulation including random torques exerted by disk turbulence due to Magneto-Rotational-Instability. For the torques, we used the semi-analytical formula developed by Laughlin et al.(2004). The damping of orbital eccentricities (in all runs) and type-I migration (in some runs) due to the tidal interactions with disk gas are also included. We found that the orbital eccentricities pumped up by the turbulent torques and associated random walks in semimajor axes tend to delay isolation of planets, resulting in more coagulation of planets than in the case without turbulence. The eccentricities are still damped after planets become isolated. As a result, the number of final planets decreases with increase in strength of the turbulence, while Earth-mass planets with small eccentricities are still formed. In the case of relatively strong turbulence, the number of final planets are 4-5 at 0.5-2AU, which is consistent with Solar system, for relatively wide range of disk surface density (~10^{-4}-10^{-2} times MMSN).