Forming Different Planetary Architectures . I . Formation Efficiency of Hot Jupites from High-eccentricity Mechanisms

TL;DR

This paper investigates the efficiency of various high-eccentricity mechanisms, including newly identified ones, in forming hot Jupiters, highlighting the dominant role of the Kozai-Lidov mechanism and proposing two distinct hot Jupiter populations.

Contribution

It introduces two new high-eccentricity mechanisms for hot Jupiter formation and compares their efficiencies, emphasizing the Kozai-Lidov mechanism's importance and identifying two hot Jupiter populations.

Findings

Kozai-Lidov mechanism is the most effective in producing hot Jupiters.

Secular chaos is less significant due to angular momentum constraints.

Two hot Jupiter populations are proposed based on formation pathways.

Abstract

Exoplanets discovered over the last decades have provided a new sample of giant exoplanets, hot Jupiters. For lack of enough materials in current locations of hot Jupiters, they are perceived to form outside snowline. Then, migrate to the locations observed through interactions with gas disks or high-eccentricity mechanisms. We examined the efficiencies of different high-eccentricity mechanisms to form hot Jupiters in near coplaner multi-planet systems. These mechanisms include planet-planet scattering, Kozai-Lidov mechanism, coplanar high-eccentricity migration, secular chaos, as well as other two new mechanisms we find in this work, which can produce hot Jupiters with high inclinations even retrograde. We find Kozai-Lidov mechanism plays the most important role in producing hot Jupiters among these mechanisms. Secular chaos is not the usual channel for the formation of hot Jupiters due to the lack of angular momentum deficit within 10^7 Tin (periods of the inner orbit). According to comparisons between the observations and simulations, we speculate that there are at least two populations of hot Jupiters. One population migrates into the boundary of tidal effects due to interactions with gas disk, such as ups And b, WASP-47 b and HIP 14810 b. These systems usually have at least two planets with lower eccentricities, and keep dynamical stable in compact orbital configurations. Another population forms through high-eccentricity mechanisms after the excitation of eccentricity due to dynamical instability. This kind of hot Jupiters usually has Jupiterlike companions in distant orbits with moderate or high eccentricities.