  Cometary dust particles are best preserved remnants of the matter present at
the onset of the formation of the Solar System. Space missions, telescopic
observations and laboratory analyses advanced the knowledge on the properties
of cometary dust. Cometary samples were returned from comet 81P/Wild2 by the
Stardust mission. The chondritic (porous) anhydrous interplanetary dust
particles and chondritic porous micrometeorites, and the ultracarbonaceous
Antarctic micrometeorites (UCAMMs) also show strong evidence for a cometary
origin. The composition of cometary dust is generally chondritic, but with high
C and N compared with CI. The cometary organic matter is mixed with minor
amounts of crystalline and amorphous minerals. The most abundant crystalline
minerals are ferromagnesian silicates, refractory minerals and low Ni Fe
sulfides are also present. The presence of carbonates in cometary dust is still
debated, but a phyllosilicate-like phase was observed in a UCAMM. GEMS phases
are usually abundant. Some of the organic matter present in cometary dust
particle resembles the insoluble organic matter present in primitive
meteorites, but amorphous carbon and exotic (e.g. N-rich) organic phases are
also present. The H isotopic composition of the organic matter traces a
formation at very low temperatures, in the protosolar cloud or in the outer
regions of the protoplanetary disk. The presolar dust concentration in cometary
dust can reach about 1%, which is the most elevated value observed in
extraterrestrial samples. The differential size distribution of cometary dust
in comet trails is well represented by a power-law distribution with a mean
power index N typically ranging from -3 to -4. Polarimetric and light
scattering studies suggest mixtures of porous agglomerates of sub-micrometer
minerals with organic matter. Cometary dust particles have low tensile
strength, and low density.
