Exoplanet Orbital Distribution around FGK Sun-like Host Stars I: planet occurrence rate derived from the Kepler Mission and theoretical interpretations from planet formation

TL;DR

This paper analyzes Kepler data to reveal the orbital distribution of exoplanets around Sun-like stars, finding a log-uniform distribution for most planets and exploring formation scenarios.

Contribution

It introduces a statistical survival function analysis to characterize exoplanet orbital distributions and discusses theoretical formation pathways.

Findings

Most planets follow a log-uniform distribution except giants.

Low occurrence rate of planets around twice Earth's radius.

Orbital distributions vary with planet size and host star properties.

Abstract

Recent astronomical observations, in particular from the Kepler and TESS missions and their related follow-ups, have revealed an abundance of exoplanets in the size range between Neptune (4 Earth radii) and Earth (1 Earth radii ), as well as a low occurrence rate of planets around twice the radius of Earth (2 Earth radii). This paper uses statistical methods, in particular, the survival function analysis, to address the known exoplanet population observed mainly from the Kepler's primary mission, in order to mathematically elucidate the orbital distributions (expressed in either the orbital period P or the orbital semi-major axis a), for each of the host stars, in both a collective way, and also separately for the planets grouped into various radius bins. We uncover a log-uniform distribution for the majority of planets except the giants. Based on the results of the statistics, we then visit several possible formation scenarios and pathways for planets in different size ranges, in order to explain the results from a theoretical point-of-view.