The intrinsic multiplicity distribution of exoplanets revealed from the radial velocity method

TL;DR

This paper introduces a method to infer the true distribution of exoplanet multiplicities from radial velocity data, accounting for observational biases, and applies it to the California Legacy Survey to reveal the prevalence of multi-planet systems.

Contribution

It develops a general approach to recover intrinsic planet multiplicity distributions from incomplete survey data and applies it to RV observations, providing new estimates of planet occurrence rates.

Findings

Approximately 20% of Sun-like stars host planets above 10 Earth masses within 1 au.

About 30-40% of these planets are in multi-planet systems.

The hot Jupiter occurrence rate is about three times higher than previous estimates.

Abstract

Planet multiplicities are useful in constraining the formation and evolution of planetary systems but usually difficult to constrain observationally. Here, we develop a general method that can properly take into account the survey incompleteness and recover the intrinsic planet multiplicity distribution. We then apply it to the radial velocity (RV) planet sample from the California Legacy Survey (CLS). Within the $1\,$au ($10\,$au) region, we find $21 \pm 4\%$ ($19.2 \pm 2.8\%$) of Sun-like stars host planets with masses above $10\,M_\oplus$ ($0.3\,M_{\rm J}$), about 30\% (40\%) of which are multi-planet systems; in terms of the RV semi-amplitude $K$, $33 \pm 7\%$ ($25 \pm 3\%$) of Sun-like stars contain planets of $K>1\,$m/s ($3\,$m/s), and each system hosts on average $1.8 \pm 0.4$ ($1.63 \pm 0.16$) planets. We note that the hot Jupiter rate in the CLS Sun-like sample is higher than the consensus value of $\sim$1\% by a factor of about three. We also confirm previous studies on the correlation between inner ($<1\,$au) and outer ($>1\,$au) planets.