Dust population of comet Halley from DUCMA experimental data.

Results from the DUCMA dust experiment on board VEGA-1 and VEGA-2 during their encounters with the nucleus of comet Halley are presented. Particles with masses from 1.5·10¹³g to 4·10^-8g were recorded in four mass intervals. The shapes of the integral mass spectra differ appreciably along the trajectory through the coma. The results show that the dust population of the coma consists of three groups: "background" particles, spiral structures, and clusters. Clusters of small particles result from relatively large particles which carry material from the surface of the nucleus and then gradually disintegrate into finer dust. This mechanism could be responsible for the transport of fine particles beyond the theoretically predicted dust paraboloid. The terminal velocities of the particles lie in the interval 300 - 400 m/sec. The apex position of these particles was found to be (50±10)·10³km.