Stellar Metallicity and the Formation of Extrasolar Gas Giant Planets

Abstract

Spectroscopic searches for extrasolar planets are most successful when the target star has high metallicity, a trend that may be caused by observational selection effects, pollution by ingested planetary material, or a requirement of high metallicity for gas giant planet formation. We show that in the scenario of the disk instability mechanism for forming gas giant protoplanets, clump-forming gravitational instabilities proceed in much the same manner in protoplanetary disks with metallicities that vary by factors of 10 greater or less than that of a standard disk model. This remarkable insensitivity to the dust grain opacity is attributed to radiative energy losses from the disks being controlled more by their being embedded in a thermal bath determined by their central protostar than by radiative fluxes deep within the disks' optically thick midplanes. This result suggests that if disk instability is the primary formation mechanism for extrasolar gas giant planets, even relatively low-metallicity galactic disk stars should harbor gas giant planets.