Thinkshop 2020

Recently, young planets with masses around $10\,M_\text{Jupiter}$ which are still embedded in a disk have been observed, e.g. in the PDS 70 system. At this mass range, the planet-disk interaction is non-linear and the planets are attributed with having carved the observed gap into their parent disk. One possible scenario for the formation of large gaps is outward migration in 2:1 mean motion resonance (MMR) where the inner planet is more massive than the outer one. This process is known to strongly excite the planets' eccentricities which in turn leads to eccentric gaps. The latter could be an observable feature of such systems.

We perform 2D, vertically integrated hydrodynamics simulations to study the migration and dynamics of the embedded planetary system employing a viscous $\alpha$-disk model. To avoid artificial wave-damping boundary conditions we choose large outer disk radii and work in the center of mass frame of the planetary system. In addition to the often used locally isothermal equation of state, we run simulations with radiative cooling, viscous heating and irradiation from the star from which temperature distributions in the perturbed disk can be extracted.

The simulations exhibit the expected smooth 2:1 MMR outward migration. For sufficiently high surface densities of the order of the minimum mass solar nebula we additionally observe epochs of fast migration. During a sequence which we call migration jumps, the outer planet undergoes fast outward migration traveling tens of au outward. It stays at the large distance for some kyr before returning back into the 2:1 MMR via fast inward migration. The whole sequence only takes 10-20 kyr. Meanwhile the inner planet remains relatively unaffected. A migration jump causes strong perturbations in the disk including pronounced spiral arms and asymmetric features including vortices and mass accumulation in the Lagrange points inside the gap region. The latter might be an observational indication for this process.

Due to the large mass of the embedded planets, the features created in the disk are strong and synthetic observations of the simulations might help to identify whether these mechanisms are at play in the disks we observe. In addition, migration jumps of massive planets can be expected to cause strong scattering of dust particles and small bodies in the radial range on which the jumps occur. Thereby, they might play an important role for the dust and small body distribution in the earlier stages of the systems lifetime.