Interstellar planetesimals: potential seeds for planet formation?

TL;DR

This study explores how interstellar objects can be captured during star formation, potentially acting as seeds for planet formation and influencing models of planetary system development and biological material distribution.

Contribution

It provides estimates of interstellar object capture rates during star and planet formation, highlighting their potential role as planetesimal seeds and emphasizing their importance in future models.

Findings

Estimated capture numbers vary widely based on assumptions.

Captured interstellar objects could serve as rapid-growth seeds for planetesimals.

Implications for biological material spread across the Galaxy.

Abstract

We investigate the trapping of interstellar objects during the early stages of star and planet formation. Our results show a very wide range of possible values that will be narrowed down as the population of interstellar objects becomes better characterized. When assuming a background number density of 2$\cdot$10$^{15}$ pc$^{-3}$ (based on 1I/'Oumuamua detection), a velocity dispersion of 30 km/s and an equilibrium size distribution, the number of interstellar objects captured by a molecular cloud and expected to be incorporated to each protoplanetary disk during its formation is O(10$^{9}$) (50 cm-5 m), O(10$^{5}$) (5 m-50 m), O(10$^{2}$) (50 m-500 m), O(10$^{-2}$) (500 m-5 km). After the disk formed, the number of interstellar objects it could capture from the ISM during its lifetime is 6$\cdot$10$^{11}$ (50 cm-5 m), 2$\cdot$10$^{8}$ (5 m-50 m), 6$\cdot$10$^{4}$ (50 m-500 m), 20 (500 m-5 km); in an open cluster where 1% of stars have undergone planet formation, these values increase by a factor of O(10$^{2}$-10$^{3}$). These trapped interstellar objects might be large enough to rapidly grow into larger planetesimals via the direct accretion of the sub-cm sized dust grains in the protoplanetary disk before they drift in due to gas drag, helping overcome the meter-size barrier, acting as "seeds" for planet formation. They should be considered in future star and planet formation models and in the potential spread of biological material across the Galaxy.