Close-in giant-planet formation via in-situ gas accretion and their natal disk properties

Aims: The origin of close-in Jovian planets is still elusive. We examine the in-situ gas accretion scenario as a formation mechanism of these planets.
Methods: We reconstruct natal disk properties from the occurrence rate distribution of close-in giant planets, under the assumption that the occurrence rate may reflect the gas accretion efficiency onto cores of these planets.
Results: We find that the resulting gas surface density profile becomes an increasing function of the distance from the central star with some structure at r ≃ 0.1 au. This profile is quite different from the standard minimum-mass solar nebula model, while our profile leads to better reproduction of the population of observed close-in super-Earths based on previous studies. We compute the resulting magnetic field profiles and find that our profiles can be fitted by stellar dipole fields (∝r^-3) in the vicinity of the central star and large-scale fields (∝r^-2) at the inner disk regions, either if the isothermal assumption breaks down or if nonideal magnetohydrodynamic effects become important. For both cases, the transition between these two profiles occurs at r ≃ 0.1 au, which corresponds to the period valley of giant exoplanets.
Conclusions: Our work provides an opportunity to test the in-situ gas accretion scenario against disk quantities, which may constrain the gas distribution of the minimum-mass extrasolar nebula.