On the various origins of close-in extrasolar planets

TL;DR

This paper analyzes the origins of close-in extrasolar planets, identifying two main types linked to different formation mechanisms—migration and scattering—using statistical methods on observed data.

Contribution

It introduces a statistical approach combining principal component and cluster analysis to distinguish two types of hot planets based on their physical parameters.

Findings

Evidence for two distinct types of hot planets.

Correlation of planet types with formation mechanisms.

Statistical separation of planets by origin.

Abstract

The extrasolar planets (EPs) so far detected are very different to the planets in our own Solar System. Many of them have Jupiter-like masses and close-in orbits (the so-called hot planets, HPs), with orbital periods of only a few days. In this paper, we present a new statistical analysis of the observed EPs, focusing on the origin of the HPs. Among the several HP formation mechanisms proposed so far, the two main formation mechanisms are type II migration and scattering. In both cases, planets form beyond the so-called snow-line of the protoplanetary disk and then migrate inward due to angular momentum and energy exchange with either the protoplanetary disk or with companion planets. Although theoretical studies produce a range of observed features, no firm correspondence between the observed EPs and models has yet been established. In our analysis, by means of principal component analysis and hierarchical cluster analysis, we find convincing indications for the existence of two types of HPs, whose parameters reflect physical mechanisms of type II migration and scattering.