Abstract
Discs around young stars are observed to form with mass budgets of tens to hundreds of Earth masses of mm-sized solids. Swarms of pebbles can self-concentrate via the streaming instability and collapse gravitationally into planetesimals larger than a kilometre in size. However, when, where, and whit what efficiency these planetesimals emerge remains poorly understood, potentially leaving a large reservoir of pebbles behind. The most massive planetesimals, in the Ceres to Pluto mass regime, can grow into cores more massive than the Earth, even beyond the water ice line, provided that leftover pebbles efficiently settle to the disc midplane. N-body simulations show that pebble accretion generically leads to systems of multiple giant planets, with a final architecture that weakly depends on the assumed initial spatial planetesimal distribution. The composition of these planets, in terms of volatile element mass budget, is regulated by thermal processing of pebbles, firstly, as they drift towards the host star and, secondly, as they are accreted and settle through a planetary envelope. New hydrodynamical simulations show that disc-embedded planets have envelopes with a convective interior and rapid disc gas advection in the outer envelope shells, allowing sublimated species to be lost to the disc. This process may have left an imprint on the moderately volatile element budget of the Earth.