Merouane, SihaneSihaneMerouaneZaprudin, BorisBorisZaprudinStenzel, OliverOliverStenzelLangevin, YvesYvesLangevinAltobelli, NicolasNicolasAltobelliDELLA CORTE, VINCENZOVINCENZODELLA CORTEFischer, HenningHenningFischerFULLE, MarcoMarcoFULLEHornung, KlausKlausHornungSilén, JohanJohanSilénLigier, NicolasNicolasLigierRotundi, AlessandraAlessandraRotundiRyno, JouniJouniRynoSchulz, RitaRitaSchulzHilchenbach, MartinMartinHilchenbachKissel, JochenJochenKisselCosima Team2020-07-162020-07-1620160004-6361http://hdl.handle.net/20.500.12386/26464Context. The COmetary Secondary Ion Mass Analyzer (COSIMA) on board Rosetta is dedicated to the collection and compositional analysis of the dust particles in the coma of 67P/Churyumov-Gerasimenko (67P). <BR /> Aims: Investigation of the physical properties of the dust particles collected along the comet trajectory around the Sun starting at a heliocentric distance of 3.5 AU. <BR /> Methods: The flux, size distribution, and morphology of the dust particles collected in the vicinity of the nucleus of comet 67P were measured with a daily to weekly time resolution. <BR /> Results: The particles collected by COSIMA can be classified according to their morphology into two main types: compact particles and porous aggregates. In low-resolution images, the porous material appears similar to the chondritic-porous interplanetary dust particles collected in Earth's stratosphere in terms of texture. We show that this porous material represents 75% in volume and 50% in number of the large dust particles collected by COSIMA. Compact particles have typical sizes from a few tens of microns to a few hundreds of microns, while porous aggregates can be as large as a millimeter. The particles are not collected as a continuous flow but appear in bursts. This could be due to limited time resolution and/or fragmentation either in the collection funnel or few meters away from the spacecraft. The average collection rate of dust particles as a function of nucleo-centric distance shows that, at high phase angle, the dust flux follows a 1/d<SUP>2</SUP><SUB>comet</SUB> law, excluding fragmentation of the dust particles along their journey to the spacecraft. At low phase angle, the dust flux is much more dispersed compared to the 1/d<SUP>2</SUP><SUB>comet</SUB> law but cannot be explained by fragmentation of the particles along their trajectory since their velocity, indirectly deduced from the COSIMA data, does not support such a phenomenon. The cumulative size distribution of particles larger than 150 μm follows a power law close to r<SUP>- 0.8 ± 0.1</SUP>, confirming measurements made by another Rosetta dust instrument Grain Impact Analyser and Dust Accumulator (GIADA). The cumulative size distribution of particles between 30 μm and 150 μm has a power index of -1.9 ± 0.3. The excess of dust in the 10-100 μm range in comparison to the 100 μm-1 mm range together with no evidence for fragmentation in the inner coma, implies that these particles could have been released or fragmented at the nucleus right after lift-off of larger particles. Below 30 μm, particles exhibit a flat size distribution. We interprete this knee in the size distribution at small sizes as the consequence of strong binding forces between the sub-constitutents. For aggregates smaller than 30 μm, forces stronger than Van-der-Waals forces would be needed to break them apart.STAMPAenArticle10.1051/0004-6361/2015279582-s2.0-85002674988000390797900019https://www.aanda.org/articles/aa/abs/2016/12/aa27958-15/aa27958-15.html2016A&A...596A..87MFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation