The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters

TL;DR

This study measures the occurrence and mass distribution of close-in exoplanets around Sun-like stars, revealing a higher prevalence of low-mass planets and challenging existing planet formation theories.

Contribution

It provides the first precise occurrence rate of close-in planets and shows that the observed population contradicts current theoretical models, indicating a need for their revision.

Findings

23% of stars host a close-in Earth-mass planet

Mass distribution follows a power law with df/dlogM = 0.39M^-0.48

Planets in the 5-30 Earth mass range are more common than models predict

Abstract

The questions of how planets form and how common Earth-like planets are can be addressed by measuring the distribution of exoplanet masses and orbital periods. We report the occurrence rate of close-in planets (with orbital periods less than 50 days) based on precise Doppler measurements of 166 Sun-like stars. We measured increasing planet occurrence with decreasing planet mass (M). Extrapolation of a power law mass distribution fitted to our measurements, df/dlogM = 0.39M^-0.48, predicts that 23% of stars harbor a close-in Earth-mass planet (ranging from 0.5 to 2.0 Earth masses). Theoretical models of planet formation predict a deficit of planets in the domain from 5 to 30 Earth masses and with orbital periods less than 50 days. This region of parameter space is in fact well populated, implying that such models need substantial revision.