High porosity for cometary dust: evidence from PROGRA experiment E. Hadamcik2, A.C. Levasseur-Regourd3, J.B. Renardb, J.C. Worms0 aAéronomie/CNRS/LPSIAJniversité PARIS VI, BP3, 91371 Verrières, France •iPCE-CNRS, 3A av. de la Recherche Scientifique, 45071 Orléans-cedex, France cESSC-ESF, Parc d'Innovation, Boulevard S. Brandt, 67400 Illkirch, France

Laboratory measurements undertaken with the PROGRA2 experiment on compact and fluffy particles floating in microgravity or lifted by an air draft are studied. The polarimetric phase curves of mixtures of aggregates of high porosity (95 to 99 %) built of submicron grains are consistent with the properties observed in cometary comae. The results suggest that the porosity of cometary particles is higher than 95 % and that their sizes may reach one millimetre.

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