Optical depth towards the nucleus of Halley's comet

Abstract

A new relation between the nuclear radius and the optical depth toward the nucleus of Comet Halley has been derived on the basis of the radial variation of the effective area of the grains along the Giotto trajectory in the coma. It is found that the expected optical depth toward the nucleus varies from 0.089 to 0.036 corresponding to the nuclear radius in the range 8 to 16 km.