  Context: The dust-brightness phase curves that have been measured by the
OSIRIS cameras on board the Rosetta spacecraft within the coma of comet
67P/Churyumov-Gerasimenko (67P) present a remarkable u-shape. Aims: Our goal is
to compare these phase curves with those of tentatively analog dust samples to
assess the key dust properties that might induce this shape. Methods:
Light-scattering measurements have been made with the PROGRA2 instrument in the
laboratory and in microgravity conditions on samples of different physical
properties and compositions that are likely to be representative of cometary
dust particles. Results: We find that the brightness phase curves of a series
of interplanetary dust analogs that have been recently developed (to fit the
polarimetric properties of the inner zodiacal cloud and their changes with
heliocentric distance) are quite comparable to those of 67P. Key dust
properties seem to be related to the composition and the porosity. Conclusions:
We conclude that the shape of the brightness phase curves of 67P has to be
related to the presence of a significant amount of organic compounds (at least
50% in mass) and of fluffy aggregates (of a size range of 10 to 200 microns).
We also confirm similarities between the dust particles of this Jupiter-family
comet and the particles within the inner zodiacal cloud.
