Planets' Heavy-element Content Trend as a Tracer for their Formation Site

Identication of the main planet formation site is the fundamental information for understanding how planets form and migrate to the current locations. We consider the heavy-element content trend of observed exoplanets that is derived from better measurements of mass and radius of these planets, and explore how the trend can be used as a tracer of their formation sites. Utilizing gas accretion recipes obtained from detailed hydrodynamical simulations, we conrm that the disk-limited gas accretion regime is most important for reproducing the heavy-element content trend. Given that such a regime is specied by two characteristic masses of planets, we compute these masses as a function of the distance (r) from the central star and examine how the regime appears in the mass-semimajor axis diagram. Our results show that a plausible solid accretion region emerges at r ' 0:6 au and expands with increasing r, using the conventional disk model. Given that exoplanets that possess the heavyelement content trend distribute currently near their central stars, our results imply the importance of planetary migration that would occur after solid accretion onto planets might be nearly completed at r 0:6 au. Self-consistent simulations are demanded for verifying our predictions.