A Flux-Based Estimate of the Interstellar Object Contribution to the Galactic Baryon Budget

This preprint presents an observation-anchored estimate of the possible Galactic mass contribution of interstellar objects (ISOs). Using the measured detection radii, encounter times, and hyperbolic velocities of the three confirmed ISOs—1I/ʻOumuamua, 2I/Borisov, and 3I/ATLAS—we derive a flux-based local ISO number density and convert it to a local mass density through a non-parametric bootstrap over the ISO masses. This density is coupled to several Galactic spatial templates constructed from the McMillan Milky Way mass model and integrated across the Galaxy to obtain the corresponding ISO mass contribution to the baryon budget. For the baryonic, total-mass, and uniform templates, modest survey incompleteness allows ISOs to supply the mass needed to bring the Milky Way baryon fraction into agreement with halo-mass expectations, while the stellar template is ruled out by orders-of-magnitude inconsistency. The repository contains the full manuscript and the analysis code required to reproduce all figures and calculations.