Friends Not Foes: Strong Correlation between Inner Super-Earths and Outer Gas Giants

Abstract

The connection between outer gas giants and inner super-Earths reflects their formation and evolutionary histories. Past work exploring this link has suggested a tentative positive correlation between these two populations, but these studies have been limited by small sample sizes and in some cases sample biases. Here we take a new look at this connection with a sample of 184 super-Earth systems with publicly available radial velocity data and resolved outer gas giants. We calculate the frequency of outer gas giants (GG) in super-Earth (SE) systems, dividing our sample into metal-rich ([Fe/H] > 0) and metal-poor ([Fe/H]≤0) hosts. We find P(GG∣SE, [Fe/H]>0) = ${28.0}_{-4.6}^{+4.9} \% $ and P(GG∣SE, [Fe/H]≤0) = ${4.5}_{-1.9}^{+2.6} \% $ . Comparing these conditional occurrence rates to field giant occurrence rates from Rosenthal et al. (2021), we show that there is a distinct positive correlation between inner super-Earths and outer gas giants for metal-rich host stars at the 2.7 σ level, but this correlation disappears for metal-poor systems. We further find that, around metal-rich stars, the GG/SE correlation enhances slightly for systems with giants that are more distant (beyond 3 au), more eccentric ( e > 0.2), and/or in multi-gas giant systems. Such trends disappear around metal-poor stars with the exception of systems of multiple giants in which we observe a tentative anti-correlation. Our findings highlight the critical role metallicity (disk solid budget) plays in shaping the overall planetary architecture.

Keywords

• Exoplanet astronomy
• Exoplanet evolution
• Exoplanet formation