We show that condensation is an efficient particle growth mechanism , leading to growth beyond decimeter-sized pebbles close to an ice line in protoplanetary discs .
As coagulation of dust particles is frustrated by bouncing and fragmentation , condensation could be a complementary , or even dominant , growth mode in the early stages of planet formation .
Ice particles diffuse across the ice line and sublimate , and vapour diffusing back across the ice line recondenses onto already existing particles , causing them to grow .
We develop a numerical model of the dynamical behaviour of ice particles close to the water ice line , approximately 3 AU from the host star .
Particles move with the turbulent gas , modelled as a random walk .
They also sediment towards the midplane and drift radially towards the central star .
Condensation and sublimation are calculated using a Monte Carlo approach .
Our results indicate that , with a turbulent \alpha -value of 0.01 , growth from millimeter to at least decimeter-sized pebbles is possible on a time scale of 1000 years .
We find that particle growth is dominated by ice and vapour transport across the radial ice line , with growth due to transport across the atmospheric ice line being negligible .
Ice particles mix outwards by turbulent diffusion , leading to net growth across the entire cold region .
The resulting particles are large enough to be sensitive to concentration by streaming instabilities , and in pressure bumps and vortices , which can cause further growth into planetesimals .
In our model , particles are considered to be homogeneous ice particles .
Taking into account the more realistic composition of ice condensed onto rocky ice nuclei might affect the growth time scales , by release of refractory ice nuclei after sublimation .
We also ignore sticking and fragmentation in particle collisions .
These effects will be the subject of future investigations .