Broadening and occultation of radio sources by comet Giacobini-Zinner as observed from ICE



During the encounter of the International Cometary Explorer (ICE) with comet P/Giacobini-Zinner, the radio astronomy experiment observed occultation and propagation effects on several distant radio sources. The observations of the partial occultation of the galactic radio source between 360 and 1000 kHz show that the 3-dimensional large scale structure of the coma is consistent with the structure determined from in-situ measurements made along the encounter trajectory. In addition, these observations remove a previously existing ambiguity in the position of the galactic source. Between 110 and 360 kHz the Earth source is broadened by scattering by the comet random density inhomogeneities. The amount of broadening indicates that the electron density fluctuations measured in situ by ICE along its trajectory (100% fluctuations with a scale length of 1 to 2 10³ km over a path length of 105 km) exist with the same properties in the perpendicular direction.