2025A&A...696A.162H

Protoplanetary disks naturally emerge during protostellar core collapse. In their early evolutionary stages, infalling material dominates their dynamical evolution. In the context of planet formation, this means that the conditions in young disks are different from the ones in the disks typically considered in which infall has subsided. High inward velocities are caused by the advection of accreted material that is deficient in angular momentum, rather than being set by viscous spreading, and accretion gives rise to strong velocity fluctuations. Therefore, we aim to investigate when it is possible for the first planetesimals to form and for subsequent planet formation to commence. We analyzed the disks obtained in numerical 3D nonideal magnetohydrodynamical simulations, which served as a basis for 1D models representing the conditions during the class 0/I evolutionary stages. We integrated the 1D models with an adapted version of the TwoPopPy code to investigate the formation of the first planetesimals via the streaming instability. In disks with temperatures such that the snow line is located at ∼10 AU and in which it is assumed that velocity fluctuations felt by the dust are reduced by a factor of 10 compared to the gas, ∼10^–3 M_⊙ of planetesimals may be formed already during the first 100 kyr after disk formation, implying the possible early formation of giant planet cores. The cold-finger effect at the snow line is the dominant driver of planetesimal formation, which occurs in episodes and utilizes solids supplied directly from the envelope, leaving the reservoir of disk solids intact. However, if the cold-finger effect is suppressed, early planetesimal formation is limited to cold disks with an efficient dust settling whose dust-to-gas ratio is initially enriched to ε₀ ≥ 0.03.