  We show that the scattering phase functions of the coma and the nucleus of
the comet 67P/Churyumov-Gerasimenko measured by the Rosetta/OSIRIS instrument
can be reproduced by a particle model involving clustered densely packed
submicrometer-sized grains composed of organic material and larger
micrometer-sized silicate grains. The simulated and measured coma phase
functions suggest that near the nucleus scattering is dominated by large
particles, and the size distribution of dust particles varies with time and/or
local coma environment. Further, we show that the measured nucleus phase
function is consistent with the coma phase function by modelling a
nucleus-sized object consisting of the same particles that explain the coma
phase functions.
