Relative occurrence rates of terrestrial planets orbiting FGK stars

TL;DR

This study maps the relative occurrence rates of terrestrial planets around FGK stars using Kepler data, revealing two abundance regions and features possibly caused by atmospheric evaporation.

Contribution

It introduces a method to correct for detection biases and derive a detailed distribution map of terrestrial planets around FGK stars.

Findings

Two main regions of planet abundance identified.

Confirmation of atmospheric evaporation effects on planet distribution.

Detection efficiency decay functions fitted to observational data.

Abstract

This paper aims to derive a map of relative planet occurrence rates that can provide constraints on the overall distribution of terrestrial planets around FGK stars. Based on the planet candidates in the Kepler DR25 data release, I first generate a continuous density map of planet distribution using a Gaussian kernel model and correct the geometric factor that the discovery space of a transit event decreases along with the increase of planetary orbital distance. Then I fit two exponential decay functions of detection efficiency along with the increase of planetary orbital distance and the decrease of planetary radius. Finally, the density map of planet distribution is compensated for the fitted exponential decay functions of detection efficiency to obtain a relative occurrence rate distribution of terrestrial planets. The result shows two regions with planet abundance: one corresponds to planets with radii between 0.5 and 1.5 R_Earth within 0.2 AU, the other corresponds to planets with radii between 1.5 and 3 R_Earth beyond 0.5 AU. It also confirms the features that may be caused by atmospheric evaporation: there is a vacancy of planets of sizes between 2.0 and 4.0 R_Earth inside of ~ 0.5 AU, and a valley with relatively low occurrence rates between 0.2 and 0.5 AU for planets with radii between 1.5 and 3.0 R_Earth.