A new interpretation of the giant planet-metallicity correlation

Since the discovery, at the Observatoire de Haute-Provence, of a planet orbiting 51 Peg in 1995, almost 300 planetary systems have been discovered. The only characteristic that distinguishes the host stars is their metallicity (the abundance of elements heavier than helium in the star atmosphere). These stars, which are mainly dwarfs (stars in the main sequence phase), are, in the mean, more metal-rich than most field objects. Up to now, this peculiarity has been interpreted as due to the enhanced rate of giant planets, or "Jupiters", formation in metal-rich circumstellar disks. A new interpretation suggests that the rate of detection of Jupiters around stars could depends on the density of H2 in the galactic disk, decreasing from the inner disk outwards. The observed correlation would then result from the presence in the solar neighbourhood of stars originating from the inner galactic disk.