  The arrival of the robustly hyperbolic asteroid A/2017 U1 has potentially
interesting ramifications for the planet-formation process. Although
extrapolations from a sample size of one are necessarily uncertain,
order-of-magnitude estimates suggest that the Galaxy contains a substantial
mass in similar bodies. We argue that despite its lack of Coma, A/2017 U1
likely contained a significant mass fraction of volatile components, and we
argue that its presence can be used to infer a potentially large population of
as-yet undetected Neptune-like extrasolar planets.
