  The discovery of 1I/`Oumuamua confirmed that planetesimals must exist in
great numbers in interstellar space. Originally generated during planet
formation, they are scattered from their original systems and subsequently
drift through interstellar space. As a consequence they should seed molecular
clouds with at least hundred-metre-scale objects. We consider how the galactic
background density of planetesimals, enriched from successive generations of
star and system formation, can be incorporated into forming stellar systems. We
find that at minimum of the order of 10$^{7}$ `Oumuamua-sized and larger
objects, plausibly including hundred-kilometre-scale objects, should be present
in protoplanetary disks. At such initial sizes, the growth process of these
seed planetesimals in the initial gas- and dust-rich protoplanetary disks is
likely to be substantially accelerated. This could resolve the tension between
accretionary timescales and the observed youth of fully-fledged planetary
systems. Our results strongly advocate that the population of interstellar
planetesimals should be taken into account in future studies of planet
formation. As not only the Galaxy's stellar metallicity increased over time but
also the density of interstellar objects, we hypothesize that this enriched
seeding accelerates and enhances planetary formation after the first couple of
generations of planetary systems.
