Planetary Formation Scenarios Revisited: Core‐Accretion versus Disk Instability

The core-accretion and disk instability models have so far been used toexplain planetary formation. These models have different conditions, such asplanet mass, disk mass, and metallicity for formation of gas giants. Thecore-accretion model has a metallicity condition ([Fe/H] > −1.17 in thecase of G-type stars), and the mass of planets formed is less than 6 times thatof the Jupiter mass MJ. On the other hand, the disk instability model does nothave the metallicity condition, but requires the disk to be 15 times moremassive compared to the minimum mass solar nebulae model. The mass of planetsformed is more than 2MJ. These results are compared to the 161 detected planetsfor each spectral type of the central stars. The results show that 90% of thedetected planets are consistent with the core-accretion model regardless of thespectral type. The remaining 10% are not in the region explained by thecore-accretion model, but are explained by the disk instability model. Wederived the metallicity dependence of the formation probability of gas giantsfor the core-accretion model. Comparing the result with the observed fractionhaving gas giants, they are found to be consistent. On the other hand, theobservation cannot be explained by the disk instability model, because thecondition for gas giant formation is independent of the metallicity.Consequently, most of planets detected so far are thought to have been formedby the core-accretion process, and the rest by the disk instability process.Comment: accepted for publication in The Astrophysical Journa