  A small admixture of dark matter gravitationally bound to the proto-Solar gas
cloud could be adiabatically contracted into Earth-crossing orbits with a local
density comparable to (or even exceeding) the Galactic halo density. We show
that a significant fraction (~25%) of the resulting 'Solar halo' would remain
today, surviving perturbations from Jupiter and close encounters with Earth,
and would be potentially observable in direct detection experiments. The
population would have distinct signatures, including a nonstandard annual
modulation and extremely low velocity dispersion compared with the Galactic
halo, making it an especially interesting target for coherent or resonant
detection of ultralight particles such as axions or dark photons.
