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

## TL;DR

This study investigates the in-situ formation of close-in giant planets by reconstructing natal disk properties from observed occurrence rates, revealing a unique gas surface density profile and magnetic field structure that differ from standard models.

## Contribution

It introduces a novel method to infer disk properties from planet occurrence data, supporting in-situ gas accretion as a viable formation mechanism for close-in giants.

## Key findings

- Reconstructed gas surface density increases with distance from star.
- Magnetic field profiles fit stellar dipole and large-scale fields.
- Disk properties differ from the standard minimum-mass solar nebula.

## Abstract

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. 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. We find that the resulting gas surface density profile becomes an increasing function of the distance from the central star with some structure at $r \simeq 0.1$ 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 ($\propto r^{-3}$) in the vicinity of the central star and large-scale fields ($\propto r^{-2}$) at the inner disk regions, either if the isothermal assumption breaks down or if nonideal MHD effects become important. For both cases, the transition between these two profiles occurs at $r \simeq 0.1$ au, which corresponds to the period valley of giant exoplanets. 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 {\it extra}solar nebula.