Second-generation dust produced by the formation of giant planets in circumstellar discs.

The observational capabilities of ALMA are providing an unprecedented view of circumstellar discs, revealing the signatures left in their gas and dust by the formation of giant planets. At the time giant planets form, planetesimals should still contain a significant fraction of the initial solid mass of the discs and their dynamical excitation by the planetary perturbations should lead to a significant collisional dust production. We investigate the dynamical and collisional evolution of the planetesimals in HD163296's circumstellar disc across the formation of its three giant planets to assess whether the second-generation dust produced by planetesimal collisions could refill the disc with dust, formerly depleted by the planetary formation process, and produce potentially observable features. We use N-body simulations and statistical methods developed for the study of the asteroid belt in the Solar System to estimate the dynamical and collisional response of the planetesimal population to the formation of the three giant planets. We took advantage of impact experiments and scaling laws to assess the outcome of the collisions among the planetesimals. Our results show that the formation of HD163296's giant planets should be followed by a global phase of dynamical excitation of the planetesimals, producing a violent collisional environment that should still be active today. The associated high impact velocities would cause a tenfold-to-hundredfold increase in the dust production by impacts, with a predicted peak in the region interior to the inner planet in agreement with observational data. The excited velocities of the planetesimals could result in the release of transient, non-equilibrium gas species like H2O due to ice sublimation during impacts and, being supersonic with respect to the gas, could produce bow shocks in the gas, possibly causing a broadening of its emission lines.