  Planet formation begins with collisional growth of small planetesimals
accumulating into larger ones. Such growth occurs while planetesimals are
embedded in a gaseous protoplanetary disc. However, small-planetesimals
experience collisions and gas-drag that lead to their destruction on short
timescales, not allowing, or requiring fine tuned conditions for the efficient
growth of $\sim$ metre-size objects. Here we show that $\sim10^{4}$
interstellar objects such as the recently detected 1I/2017-U1 ('Oumuamua) could
have been captured, and become part of the young Solar System, together with up
to hundreds of $\sim$ km sized ones. The capture rates are robust even for
conservative assumptions on the protoplanetary disc structure, local stellar
environment and planetesimal ISM density. 'Seeding' of such planetesimals then
catalyze further planetary growth into planetary embryos, and potentially
alleviate the main-challenges with the meter-size growth-"barrier". The capture
model is in synergy with the current leading planet formation theories,
providing the missing link to the first planetesimals. Moreover, planetesimal
capture provides a far more efficient route for lithopanspermia than previously
thought.
