  We show that an equal-mass, temporary binary companion to the Sun in the
solar birth cluster at a separation of $\sim 10^3 \; \mathrm{\; AU}$ would have
increased the likelihood of forming the observed population of outer Oort cloud
objects and of capturing Planet Nine. In particular, the discovery of a
captured origin for Planet Nine would favor our binary model by an order of
magnitude relative to a lone stellar history. Our model predicts an
overabundance of dwarf planets, discoverable by LSST, with similar orbits to
Planet Nine, which would result from capture by the stellar binary.
