The California Legacy Survey II. Occurrence of Giant Planets Beyond the Ice line

TL;DR

This study uses high-precision radial velocity data to map the occurrence of giant planets around FGKM stars, revealing a peak near 1 au and a decrease beyond 8 au, with implications for planet formation theories.

Contribution

It provides the first detailed occurrence rates of giant planets across a wide range of orbital distances, highlighting a significant increase near 1 au and a decline at larger separations.

Findings

Giant planets are most common at 1-10 au.

Occurrence rate of giant planets decreases beyond 8 au.

Sub-Jovian planets also show increased occurrence near 1-10 au.

Abstract

We used high-precision radial velocity measurements of FGKM stars to determine the occurrence of giant planets as a function of orbital separation spanning 0.03-30 au. Giant planets are more prevalent at orbital distances of 1-10 au compared to orbits interior or exterior of this range. The increase in planet occurrence at $\sim$1 au by a factor of $\sim$4 is highly statistically significant. A fall-off in giant planet occurrence at larger orbital distances is favored over models with flat or increasing occurrence. We measure $14.1^{+2.0}_{-1.8}$ giant planets per 100 stars with semi-major axes of 2-8 au and $8.9^{+3.0}_{-2.4}$ giant planets per 100 stars in the range 8-32 au, a decrease in giant planet occurrence with increasing orbital separation that is significant at the $\sim$2$\sigma$ level. We find that the occurrence rate of sub-Jovian planets (0.1-1 Jupiter masses) is also enhanced for 1-10 au orbits. This suggests that lower mass planets may share the formation or migration mechanisms that drive the increased prevalence near the water-ice line for their Jovian counterparts. Our measurements of cold gas giant occurrence are consistent with the latest results from direct imaging surveys and gravitational lensing surveys despite different stellar samples. We corroborate previous findings that giant planet occurrence increases with stellar mass and metallicity.