The California Legacy Survey III. On The Shoulders of (Some) Giants: The\n Relationship between Inner Small Planets and Outer Massive Planets

Abstract

We use a high-precision radial velocity survey of FGKM stars to study the\nconditional occurrence of two classes of planets: close-in small planets\n(0.023--1 au, 2--30 Earth masses) and distant giant planets (0.23--10 au,\n30--6000 Earth masses). We find that $41^{+15}_{-13}\\%$ of systems with a\nclose-in, small planet also host an outer giant, compared to\n$17.6^{+2.4}_{-1.9}\\%$ for stars irrespective of small planet presence. This\nimplies that small planet hosts may be enhanced in outer giant occurrence\ncompared to all stars with $1.7\\sigma$ significance. Conversely, we estimate\nthat $42^{+17}_{-13}\\%$ of cold giant hosts also host an inner small planet,\ncompared to $27.6^{+5.8}_{-4.8}\\%$ of stars irrespective of cold giant\npresence. We also find that more massive and close-in giant planets are not\nassociated with small inner planets. Specifically, our sample indicates that\nsmall planets are less likely to host outer giant companions more massive than\napproximately 120 Earth masses and within 0.3--3 au than to host less massive\nor more distant giant companions, with $\\sim$2.2$\\sigma$ confidence. This\nimplies that massive gas giants within 0.3--3 au may suppress inner small\nplanet formation. Additionally, we compare the host-star metallicity\ndistributions for systems with only small planets and those with both small\nplanets and cold giants. In agreement with previous studies, we find that stars\nin our survey that only host small planets have a metallicity distribution that\nis consistent with the broader solar-metallicity-median sample, while stars\nthat host both small planets and gas giants are distinctly metal-rich with\n$\\sim$2.3$\\sigma$ confidence.\n