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tokens: are often referred to as pebbles . Pebbles interact with the gas disc through gas drag and drift inwards ( Weidenschilling 1977 ; Brauer et al. 2008 ). Pebbles can become concentrated in pressure bumps and through the streaming instability (see Johansen et al. 2014 for a review), leading to planetesimal formation by gravitational collapse of the filaments. Planetesimals formed by the streaming instability have characteristic sizes of 100 km ( Johansen et al. 2015 ; Simon et al. 2015 ). In classical planet formation models, the cores of the giant planets form through mutual collisions between these planetesimals ( Pollack et al. 1996 ). However, to achieve a core mass high enough (≈10 M E ) to attract a gaseous envelope, a surface density of planetesimals of a few times the Minimum Mass Solar Nebula (MMSN) is needed. Additionally, the growth timescale increases steeply with orbital distance, making the formation of the ice giants in the solar system basically impossible to achieve with planetesimal accretion alone. Gravitational stirring of the planetesimals by a set of growing protoplanets decreases the growth rates even more ( Levison et al. 2010 ). In recent years, a new paradigm of solid accretion has emerged: pebble accretion ( Johansen Lacerda 2010 ; Ormel Klahr 2010 ; Lambrechts Johansen 2012 ; Morbidelli Nesvorny 2012 ). When a pebble enters the planetary Hill sphere, it is subject to gas drag, which robs the pebble of angular momentum, resulting in an inward drift of the pebble onto the planet. When the largest planetesimals have grown to a few hundred kilometers in size by accreting other planetesimals, rapid pebble accretion allows further growth to cores of ten Earth masses well within the lifetime of the protoplanetary disc ( Ida et al. 2016 ; Visser Ormel 2016 ; Johansen Lambrechts 2017 ). A growing planet opens a partial gap in the protoplanetary gas disc, which influences the motion of solids in the disc ( Paardekooper Mellema 2006 ; Rice et al. 2006 ). Pebble accretion stops when the gap carved by the planet generates a pressure maximum outside of its orbit, which stops the inward flux of pebbles ( Morbidelli Nesvorny 2012 ; Lambrechts et al. 2014 ). This is referred to as the pebble-isolation mass. As the influx of pebbles is stopped, the planet’s gas envelope loses its hydrostatic support, and the envelope can then contract to form a planet with an extensive gaseous atmosphere ( Lambrechts et al. 2014 ). In the solar system, pebble isolation is a potential mechanism to explain the dichotomy between the ice and gas giants, with ice giants never reaching the pebble-isolation mass and hence not able to undergo gas accretion within the lifetime of the protoplanetary disc ( Lambrechts et al. 2014 ; Venturini Helled 2017 ; Frehlik Murray-Clay 2017 ). Lambrechts et al. (2014) used hydrodynamical simulations to infer a pebble-isolation mass given by where H ∕ r is the discs aspect ratio. Lambrechts et al. (2014) found a weak