Growing the seeds of pebble accretion through planetesimal accretion

We explore the growth of planetary embryos by planetesimal accretion up to and beyond point at which pebble becomes efficient so-called Hill-transition mass. Both transition mass characteristic planetesimals that formed streaming instability increase with increasing distance from star. developed a model for large (embryo) embedded in population smaller filament instability. The includes self-consistent way collisional embryo, fragmentation planetesimals, velocity evolution all involved bodies, viscous spreading filament. find embryo accretes available material during lifetime protoplanetary disc only inner regions disc. In contrast, we little or no outer parts 5-10 AU. Overall, our results demonstrate very long timescales giant planets form. This means order form cold orbits, must act directly on largest bodies present initial function help mutual collisions.