Electrostatic and rotational ejection of dust particles from a disintegrating cometary aggregate

Assuming that small fragments are released and ejected from the surface of cometary dust aggregate, a simple model of the secondary particle population around and antisunward of the aggregate is developed. First, formylae are derived for the velocity of a fragment ejected due to electrostatic charging and rotation of the aggregate. Then, characteristics of the resulting mini-fountain are analysed as functions of the fragment size. It is shown that for fragments less than ∼ 10−14 g the electrostatic ejection dominates, and the apex distance increases rapidly with decreasing secondary particle mass reaching ∼ 103 km at m ∼ 10−17 g. For medium and large secondary particles the rotational ejection prevaila, with typical distances to apex of the order of 0.1 km. The time during which a fragment reaches the apex is of the order of 1 min for micron-sized particles, and increases towards both smaller and larger sizes. Furthermore, the time needed to separate a fragment from the aggregate by a distance l and the radius of the fountain envelope are both evaluated as functions of l. All the quantities under consideration are also investigated as functions of the heliocentric distance. Finally, formulae for dust fluences to be recorded during a spacecraft passage through the mini-fountain are derived and discussed.