The Intrinsic Multiplicity Distribution of Exoplanets Revealed from the Radial Velocity Method. II. Constraints on Giant Planet Multiplicity from Different Surveys

TL;DR

This study derives the intrinsic multiplicity distribution of giant exoplanets within 10 au from Sun-like stars using two RV surveys, revealing lower multiplicity than some models predict and highlighting survey differences.

Contribution

It provides the first detailed comparison of giant planet multiplicity distributions from independent RV surveys, refining the understanding of planetary system architectures.

Findings

7.8% of Sun-like stars have one giant planet within 10 au in HARPS

15.8% of Sun-like stars have at least one giant planet within 10 au in CLS

Most theoretical models involving planet-planet scattering predict too many multi-giant systems.

Abstract

Compared to the commonly used planet occurrence rates, the multiplicity distribution of planets can be more useful in constraining the formation and evolution pathways of planetary systems. This work follows an earlier work of Zhu (2022) and derive the intrinsic multiplicity distribution of giant planets (with masses above Saturn mass) from two independent radial velocity (RV) surveys. In particular, we find that $(7.8\pm1.4\%, 2.3\pm1.2\%, 0.5^{+0.8}_{-0.3}\%)$ of Sun-like stars in the HARPS sample have $(1, 2, 3)$ giant planets within 10\,au, whereas $(7.3\pm2.8\%, 7.2\pm2.3\%, <1.3\%, 1.0^{+1.0}_{-0.6}\%)$ of Sun-like stars in the California Legacy Survey (CLS) have $(1, 2, 3, 4)$ giant planets within 10\,au. Here we have further cleaned the CLS sample and removed planet detections that were not discovered in the survey mode. The total fraction of Sun-like stars with at least one giant planet within 10\,au from the two samples are $10.6\pm1.2\%$ and $15.8\pm2.1\%$, respectively, and the difference may be accounted for by their different metallicity distributions. We briefly discuss the theoretical implications of our results. In particular, the inferred giant planet multiplicity distribution is inconsistent with most of the proposed theoretical models involving planet--planet scatterings, which predict too many multi-giant systems.