Implications of the TTV-detection of close-in terrestrial planets around M stars for their origin and dynamical evolution

N Haghighipour,S Rastegar

doi:10.1051/epjconf/20101104004

Abstract

It has been shown that an Earth-size planet or a super-Earth, in resonance with a transiting Jupiter-like body in a short-period orbit around an M star, can create detectable TTV signals (Kirste \& Haghighipour, 2011). Given the low masses of M stars and their circumstellar disks, it is expected that such a transiting giant planet to have formed at large distances and migrated to its close-in orbit. That implies, if such systems are discovered around M stars, the terrestrial planet had to form during the migration of the giant planet. The formation of this object may be either in-situ (in a close-in orbit) followed by its capture in resonance, or the object is formed at larger distances where it was subsequently captured in a resonance with the migrating giant planet. We have investigated these two scenarios by simulating the dynamics of a disk of protoplanetary embryos and the formation of terrestrial planets during the migration of a Jupiter-like planet around an M star. Results suggest that unless the migration of the giant planet is very slow (slower than 1E-7 AU/year), it is unlikely that the close-in terrestrial planet is formed in-situ. If a terrestrial planet is detected in a mean-motion resonance with a close-in giant planet around an M star, the terrestrial planet was most likley formed at large distances and carried to its close-in resonant orbit by the migrating giant body.

Highlights

In searching for potentially habitable planets, M stars present the most promising targets
To simulated the formation of terrestrial planets during the migration of a Jupiter-like body around an M star, we considered a model consisting of a star, a protoplanetary disk, and a Jupiter-size planet
Simulations results indicate that for both disks models and all migration rates, terrestrial planets were formed in the protoplanetary disk, they did not maintain stability and were ejected from the system

Summary

Introduction

In searching for potentially habitable planets, M stars present the most promising targets. Examples can be found in the works of Zhou et al (2005), Fog & Nelson (2005, 2007a&b, 2009), Raymond et al (2006), Mandell et al (2007), and Kennedy & Kenyon (2008) As shown by these authors, a migrating giant planet may capture protoplanetary objects in mean-motion resonances and increase their orbital eccentricities to high values. If during the migration of the giant planet, substantial amount of gas still exists, the combination of gas drag and dynamical friction may prevent the eccentricities of planetary embryos to reach high values and may facilitate their growth to larger objects Simulations by these authors have shown that, an Earth-size planet can form around a Sun-like star while a Jupiter-mass body migrates through the disk of planetary embryos and the system is subject to gas drag. In order to examine the viability of the scenario presented by these authors, simulations of terrestrial planet formation have to be carried out for a migrating giant planet in a disk of planetary embryos while allowing the giant planet to migrate to very close-in orbits

Numerical Simulations and the Results

Findings

Conclusions