We consider the effects of Galactic substructure on energetic neutrinos from
annihilation of weakly-interacting massive particles (WIMPs) that have been
captured by the Sun and Earth. Substructure gives rise to a time-varying
capture rate and thus to time variation in the annihilation rate and resulting
energetic-neutrino flux. However, there may be a time lag between the capture
and annihilation rates. The energetic-neutrino flux may then be determined by
the density of dark matter in the Solar System's past trajectory, rather than
the local density. The signature of such an effect may be sought in the ratio
of the direct- to indirect-detection rates.Comment: 4 pages, 4 figures. Replaced with version accepted for publicatio