Pebble-driven planet formation around stars of different masses
Abstract
Observational breakthrough has been achieved in characterizing the properties of protoplanetary disks and extrasolar planets in the last decade. We thus gain a better understanding on both the birth conditions and the end products of planets. Meanwhile, more advanced theoretical and numerical models are required to establish the bridge between these two based on evolving planet formation theories. We develop the pebble-driven core accretion model to study the formation and evolution of planets around stars in the range of 0.08 MSun and 1 MSun. By Monte Carlo sampling of their initial conditions, the growth and migration of a large number of individual protoplanetary embryos are simulated in a population synthesis mannar. Two hypothesis are proposed for the birth locations of embryos, at the water ice line or log-uniformly distributed over distance in protoplanetary disks. Two types of disks with different turbulent viscous parameters αt of 10-3 and 10-4 are also investigated. The forming planet population is statistically compared with the observed exoplanets in terms of mass, semimajor axis, metallicity and water content. We find that massive planets are likely to form when the characteristic disk sizes are larger, the disk accretion rates are higher, the disks are more metal rich and/or their stellar hosts are more massive. Our model shows that 1) the characteristic planet mass is set by the pebble isolation mass. It increases linearly with the stellar mass, corresponding to one Earth mass around a Trappist-1 star and 20 Earth mass around a solar-mass star. 2) The low-mass planets up to 20 ME can form around stars with a wide range of metallicities, while massive gas giant planets are preferred to grow around metal rich stars. 3) The super-Earth planets mainly composed of silicates with relatively low water fractions can form from the seeds at the water ice line in less turbulent disks. Altogether, the model succeeds in quantitatively reproducing several important observed properties and correlations among exoplanets.
- Publication:
-
AAS/Division for Extreme Solar Systems Abstracts
- Pub Date:
- August 2019
- Bibcode:
- 2019ESS.....431704B