Growth and Evolution of Planets in protoplanetary Disks

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As of today over 2600 exoplanetary systems that contain over 3500 planets have been discovered. The debiased observations show that the most abundant planets are Super-Earths (planets with 1-20 Earth masses) with orbital periods shorter than 100 days, followed by giant planets at distances of 1-3 astronomical units (AU) from the parent star. The latter outnumber, by at least a factor of ten, the population of hot-Jupiters (at a distance of about 0.1 AU from the star). The mass distribution of giant planets peaks at about 1-3 Jupiter masses; planets with masses larger than that exist but are quite rare. From a theoretical standpoint, these observations are difficult to understand. Planet migration towards the star can easily explain the existence of close-in super-Earths, but it is a problem to understand why only a minority of giant planets reached orbits less than 1 AU in semi major axis. Also, gas accretion onto planetary cores should be very fast. Thus, it is not understood what prevented super-Earths from becoming giant planets and what limited the growth of giant planets to a few Jupiter masses.This proposal is based on the idea that the difficulties in understanding the extrasolar planets' mass and orbital distributions are due to incorrect assumptions on the protoplanetary disk structure. The classic view of a viscous disk, with viscosity generated by strong turbulence driven by the magneto rotational instability, is challenged by modern magneto-hydrodynamic simulations. Disks are probably much less viscous than previously thought. Nevertheless, disks cannot be inviscid, a minimum viscosity is set for example by the so-called vertical shear instability (VSI). In addition, disk winds remove angular momentum from thin surface layers of the protoplanetary disk, promoting the fast radial transport of gas towards the central star in these layers. Our proposed project is (i) to construct a realistic model of protoplanetary disks accounting for both the VSI and disk winds, and reproducing the observed stellar accretion rates and (ii) to study the accretion of gas and the migration of planets embedded in these disks.