Planetesimal and planet formation in transient dust traps

The ring-like structures in protoplanetary discs that are observed in the cold dust emission by ALMA, might be explained by dust aggregates trapped aerodynamically in pressure maxima. The effect of a transient pressure maximum is investigated that develops between two regimes with different turbulent levels. We study how such a pressure maximum collects dust aggregates and transforms them into large planetesimals and Moon-mass cores that can further grow to a few Earth-mass planets by pebble accretion, and eventually to giant planets, by considering the accretion of a gaseous envelope. A numerical model is developed, incorporating the evolution of gaseous disc, growth and transport of pebbles, N-body interactions of growing planetary cores and their backreaction to gas disc by opening a partial gap. Planetesimal formation by streaming instability is parametrized in our model. A transient pressure maximum efficiently accumulates dust particles that can grow larger than mm-size. If this happens, dust aggregates can be transformed by the streaming instability process into such large planetesimals, which can grow further by pebble accretion, according to our assumptions. As the gas evolves to its steady state, the pressure maximum vanishes, and the concentrated pebbles that are not transformed to planetesimals and accreted by the growing planet, drift inward. During this inward drift, if the conditions of the streaming instability are met, planetesimals are formed in a wide radial range of the disc. Conclusions. A transient pressure maximum is a favourable place for planetesimal and planet formation during its lifetime and the concentration of pebbles induces continuous formation of planetesimals even after its disappearance. Besides, the formation of a planet can trigger the formation of planetesimals over a wide area of the protoplanetary disc.