  The compositions of planet-forming disks are set by a combination of material
inherited from the interstellar medium and material reprocessed during disk
formation and evolution. Indeed, comets and primitive meteorites exhibit
interstellar-like isotopic ratios and/or volatile compositions, supporting that
some pristine material was incorporated intact into icy planetesimals in the
Solar Nebula. To date, the survival of volatile interstellar material in the
disk stage has not been modeled using realistic disk physics. Here, we present
a modeling framework to track the destruction of interstellar ices on dust
grains undergoing transport processes within a disk, with a particular focus on
explaining the incorporation of pristine material into icy planetesimals. We
find it is difficult to explain inheritance through the local assembly of
comets, as ice destruction is rapid for small (<10um) grains in the inner few
tens of au. Instead, a plausible pathway to inheritance is to form pebbles at
larger disk radii, which then drift inwards to the comet-forming zone with
their ices mostly preserved. Small grains beyond ~100 au can experience ice
photodissociation at the tens of percent level, however little of the ice is
actually lost from the grain, likely making this a robust site for in situ ice
chemistry. Our models also indicate that many complex organic species should
survive passage through the disk intact. This raises the possibility that
organics synthesized in the interstellar medium can be delivered to terrestrial
planets by icy body impact and thus potentially participate in origins of life
chemistry.
