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Cometary dust particles are best preserved remnants of the matter present atthe onset of the formation of the Solar System. Space missions, telescopicobservations and laboratory analyses advanced the knowledge on the propertiesof cometary dust. Cometary samples were returned from comet 81P/Wild2 by theStardust mission. The chondritic (porous) anhydrous interplanetary dustparticles and chondritic porous micrometeorites, and the ultracarbonaceousAntarctic micrometeorites (UCAMMs) also show strong evidence for a cometaryorigin. The composition of cometary dust is generally chondritic, but with highC and N compared with CI. The cometary organic matter is mixed with minoramounts of crystalline and amorphous minerals. The most abundant crystallineminerals are ferromagnesian silicates, refractory minerals and low Ni Fesulfides are also present. The presence of carbonates in cometary dust is stilldebated, but a phyllosilicate-like phase was observed in a UCAMM. GEMS phasesare usually abundant. Some of the organic matter present in cometary dustparticle resembles the insoluble organic matter present in primitivemeteorites, but amorphous carbon and exotic (e.g. N-rich) organic phases arealso present. The H isotopic composition of the organic matter traces aformation at very low temperatures, in the protosolar cloud or in the outerregions of the protoplanetary disk. The presolar dust concentration in cometarydust can reach about 1%, which is the most elevated value observed inextraterrestrial samples. The differential size distribution of cometary dustin comet trails is well represented by a power-law distribution with a meanpower index N typically ranging from -3 to -4. Polarimetric and lightscattering studies suggest mixtures of porous agglomerates of sub-micrometerminerals with organic matter. Cometary dust particles have low tensilestrength, and low density.

Chemical and physical properties of cometary dust