  We present Hubble Space Telescope optical coronagraphic polarization imaging
observations of the dusty debris disk HD 61005. The scattered light intensity
image and polarization structure reveal a highly inclined disk with a clear
asymmetric, swept back component, suggestive of significant interaction with
the ambient interstellar medium. The combination of our new data with the
published 1.1 micron discovery image shows that the grains are blue scattering
with no strong color gradient as a function of radius, implying predominantly
sub-micron sized grains. We investigate possible explanations that could
account for the observed swept back, asymmetric morphology. Previous work has
suggested that HD 61005 may be interacting with a cold, unusually dense
interstellar cloud. However, limits on the intervening interstellar gas column
density from an optical spectrum of HD 61005 in the Na I D lines render this
possibility unlikely. Instead, HD 61005 may be embedded in a more typical warm,
low-density cloud that introduces secular perturbations to dust grain orbits.
This mechanism can significantly distort the ensemble disk structure within a
typical cloud crossing time. For a counterintuitive relative flow
direction--parallel to the disk midplane--we find that the structures generated
by these distortions can very roughly approximate the HD 61005 morphology.
Future observational studies constraining the direction of the relative
interstellar medium flow will thus provide an important constraint for future
modeling. Independent of the interpretation for HD 61005, we expect that
interstellar gas drag likely plays a role in producing asymmetries observed in
other debris disk systems, such as HD 15115 and Delta-Velorum.
