Planet seeding through gas-assisted capture of interstellar objects

Abstract

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.