  The origin of the interstellar object 1I/'Oumuamua, has defied explanation.
In a companion paper (Jackson & Desch, 2021), we show that a body of N2 ice
with axes 45 m x 44 m x 7.5 m at the time of observation would be consistent
with its albedo, non-gravitational acceleration, and lack of observed CO or CO2
or dust. Here we demonstrate that impacts on the surfaces of Pluto-like Kuiper
belt objects (KBOs) would have generated and ejected ~10^14 collisional
fragments--roughly half of them H2O ice fragments and half of them N2 ice
fragments--due to the dynamical instability that depleted the primordial Kuiper
belt. We show consistency between these numbers and the frequency with which we
would observe interstellar objects like 1I/'Oumuamua, and more comet-like
objects like 2I/Borisov, if other stellar systems eject such objects with
efficiency like that of the Sun; we infer that differentiated KBOs and
dynamical instabilities that eject impact-generated fragments may be
near-universal among extrasolar systems. Galactic cosmic rays would erode such
fragments over 4.5 Gyr, so that fragments are a small fraction (~0.1%) of
long-period Oort comets, but C/2016 R2 may be an example. We estimate 'Oumuamua
was ejected about 0.4-0.5 Gyr ago, from a young (~10^8 yr) stellar system,
which we speculate was in the Perseus arm. Objects like 'Oumuamua may directly
probe the surface compositions of a hitherto-unobserved type of exoplanet:
"exo-plutos". 'Oumuamua may be the first sample of an exoplanet brought to us.
