Forming Close-in Earth-like Planets via a Collision-Merger Mechanism in Late-stage Planet Formation

TL;DR

This paper demonstrates through dynamical simulations that late-stage planetary embryo collisions can produce close-in Earth-like planets, providing insight into their formation after gas dissipation.

Contribution

It introduces a collision-merger mechanism during late-stage planet formation that can form close-in terrestrial planets from planetary embryo impacts.

Findings

Collision-mergers can place terrestrial planets very close to their stars.

Dynamical simulations support the collision-merger mechanism.

The process explains the origin of close-in Earth-like exoplanets.

Abstract

The large number of exoplanets found to orbit their host stars in very close orbits have significantly advanced our understanding of the planetary formation process. It is now widely accepted that such short-period planets cannot have formed {\em in situ}, but rather must have migrated to their current orbits from a formation location much farther from their host star. In the late stages of planetary formation, once the gas in the proto-planetary disk has dissipated and migration has halted, gas-giants orbiting in the inner disk regions will excite planetesimals and planetary embryos, resulting in an increased rate of orbital crossings and large impacts. We present the results of dynamical simulations for planetesimal evolution in this later stage of planet formation. We find that a mechanism is revealed by which the collision-merger of planetary embryos can kick terrestrial planets directly into orbits extremely close to their parent stars.