Massive exoplanets are observed preferentially around high metallicity ( [ Fe/H ] ) stars while low-mass exoplanets do not show such an effect .
This so-called planet-metallicity correlation generally favors the idea that most observed gas giants at r < 10 AU are formed via a core accretion process .
We investigate the origin of this phenomenon using a semi-analystical model , wherein the standard core accretion takes place at planet traps in protostellar disks where rapid type I migrators are halted .
We focus on the three major exoplanetary populations - hot-Jupiters , exo-Jupiters located at r \simeq 1 AU , and the low-mass planets .
We show using a statistical approach that the planet-metallicity correlations are well reproduced in these models .
We find that there are specific transition metallicities with values [ Fe/H ] = -0.2 to -0.4 , below which the low-mass population dominates , and above which the Jovian populations take over .
The exo-Jupiters significantly exceed the hot-Jupiter population at all observed metallicities .
The low-mass planets formed via the core accretion are insensitive to metallicity , which may account for a large fraction of the observed super-Earths and hot-Neptunes .
Finally , a controlling factor in building massive planets is the critical mass of planetary cores ( M _ { c,crit } ) that regulates the onset of runaway gas accretion .
Assuming the current data is roughly complete at [ Fe/H ] > -0.6 , our models predict that the most likely value of the ” mean ” critical core mass of Jovian planets is \langle M _ { c,crit } \rangle \simeq 5 M _ { \oplus } rather than 10 M _ { \oplus } .
This implies that grain opacities in accreting envelopes should play an important role in lowering M _ { c,crit } .