  We compute, for the first time, self-consistent models of planet growth
including the effect of envelope enrichment. The change of envelope metallicity
is assumed to be the result of planetesimal disruption or icy pebble
sublimation. We solve internal structure equations taking into account global
energy conservation for the envelope to compute in-situ planetary growth. We
consider different opacities and equations of state suited for a wide range of
metallicities. We find that envelope enrichment speeds up the formation of gas
giants. It also explains naturally the formation of low and intermediate mass
objects with large fractions of H-He (~ 20 - 30 % in mass). High opacity models
explain well the metallicity of the giant planets of the solar system, whereas
low opacity models are suited for forming small mass objects with thick H-He
envelopes and gas giants with sub-solar envelope metallicities. We find good
agreement between our models and the estimated water abundance for WASP-43b.
For HD 189733b, HD 209458b and WASP-12b we predict fractions of water larger
than what is estimated from observations, by at least a factor ~ 2. Envelope
enrichment by icy planetesimals is the natural scenario to explain the
formation of a large variety of objects, ranging from mini-Neptunes, to gas
giants. We predict that the total and envelope metallicity decrease with
planetary mass.
