Revealing a Universal Planet-Metallicity Correlation for Planets of Different Sizes Around Solar-type Stars

The metallicity of exoplanet systems serves as a critical diagnostic of planet formation mechanisms. Previous studies have demonstrated the planet-metallicity correlation for large planets ({{R}_P} ≥slant 4 {{R}_E}); however, a correlation has not been found for smaller planets. With a sample of 406 Kepler objects of interest whose stellar properties are determined spectroscopically, we reveal a universal planet-metallicity correlation: not only gas-giant planets (3.9 {{R}_E} \lt {{R}_P} ≤slant 22.0 {{R}_E}) but also gas-dwarf (1.7 {{R}_E} \lt {{R}_P} ≤slant 3.9 {{R}_E}) and terrestrial planets ({{R}_P} ≤slant 1.7 {{R}_E}) occur more frequently in metal-rich stars. The planet occurrence rates of gas-giant planets, gas-dwarf planets, and terrestrial planets are 9.30_-3.04^+5.62, 2.03_-0.26^+0.29, and 1.72_-0.17^+0.19 times higher for metal-rich stars than for metal-poor stars, respectively.