  We have obtained Hubble Space Telescope STIS and NICMOS, and Gemini/GPI
scattered light images of the HD 191089 debris disk. We identify two spatial
components: a ring resembling Kuiper Belt in radial extent (FWHM: ${\sim}$25
au, centered at ${\sim}$46 au), and a halo extending to ${\sim}$640 au. We find
that the halo is significantly bluer than the ring, consistent with the
scenario that the ring serves as the "birth ring" for the smaller dust in the
halo. We measure the scattering phase functions in the 30{\deg}-150{\deg}
scattering angle range and find the halo dust is both more forward- and
backward-scattering than the ring dust. We measure a surface density power law
index of -0.68${\pm}$0.04 for the halo, which indicates the slow-down of the
radial outward motion of the dust. Using radiative transfer modeling, we
attempt to simultaneously reproduce the (visible) total and (near-infrared)
polarized intensity images of the birth ring. Our modeling leads to mutually
inconsistent results, indicating that more complex models, such as the
inclusion of more realistic aggregate particles, are needed.
