Determination of the coma dust back-scattering of 67P for phase angles from 1.2° to 75°

Trial scattering calculations demonstrate that the observed strong backscattering most likely arises from particles in the size range 1-20 µm. Our observed backscattering phase curve gives no constraints on the real index of refraction, the particle size distribution or the minimum and maximum particle size cut-offs. However, an upper limit to the imaginary index of refraction of ∼0.01 was required, making these particles quite transparent. Simple spherical scattering calculations including particle size distributions can fit the general characteristics of the phase curve but cannot produce a satisfactory detailed fit.