On hypervelocity impact phenomena of microdust and nano X-ray flares in cometary comae

Dust measurements on the Vega and Giotto probes to Comet Halley have shown that dust particles of very small sizes (10-100 A) might be very abundant in cometary comas. A scenario of self-generation of such population of very small grains (VSGs) via collisional interaction with the cometary dust coma is considered here. If the VSGs can be charged to an electrostatic potential of greater than or similar to 10 V, they would be effectively trapped by electromagnetic interaction with the cometary plasma and the collisional erosion of the cometary dust coma would be facilitated. In the case that a small fraction of the impact kinetic energy can be converted to soft X-ray emission, the resultant X-ray luminosity might reach 5-10% of the value observed by ROSAT thus providing a second component of the source mechanism. (C) 1997 Academic Press.