Properties of dust particles in comets from polarimetric observations of 67P

Cometary activity changes considerably when comets approach the Sun. Jets can be observed in polarization maps, allowing interpretations in terms of properties of the dust particles. We summarize polarimetric observations of 67P/Churyumov-Gerasimenko during its 2008- 09 apparition, between solar distances of 1.26 au and 1.45 au (before and after perihelion). We present observations from Hubble Space Telescope at 2.56 au and 1.64 au, before and after perihelion, respectively, and photometric observations from Himalayan Chandra telescope (India). Interpretation of such observations will be discussed, taking into account Rosetta results on dust particles. We will also compare 67P polarimetric properties with those of other JFC comets (47P, 81P, 22P), and of 1P/Halley and Oort cloud comets at similar solar distances. *On behalf of the HST Comet Polarimetry Team.