  We provide a calculation of Pan-STARRS' ability to detect objects similar to
the interstellar object 1I/2017 U1 (hereafter 'Oumuamua), including the most
detectable approach vectors and the effect of object size on detection
efficiency. Using our updated detection cross-section, we infer an interstellar
number density of such objects ($n_{IS} \approx 0.2~\rm{au}^{-3}$). This
translates to a mass density of $\rho_{IS} \approx 4M_\oplus~\rm{pc}^{-3}$
which cannot be populated unless every star is contributing. We find that given
current models, such a number density cannot arise from the ejection of inner
solar system material during planet formation. We note that a stellar system's
Oort cloud will be released after a star's main sequence life time and may
provide enough material to obtain the observed density. The challenge is that
Oort cloud bodies are icy and \OBJECT was observed to be dry which necessitates
a crust generation mechanism.
