Dust distribution of comet P/Halley’s inner coma determined from the Giotto Radio-Science Experiment

Measurements of the Giotto Radio-Science Experiment, consisting of the Doppler frequency shift and the intensity level of the X-band downlink signal of the Giotto spacecraft during Halley encounter, are analysed and interpreted. Continuous radio-science data were recorded throughout the encounter. The Doppler shift observed over a time interval of about 100 s is attributed to a drag effect in the cometary atmosphere causing a deceleration of the spacecraft. The total change of velocity of Giotto was 23.05 ± 0.05 cm s−1, yielding a best estimate for the total cometary mass impacting the spacecraft of 0.32 g. The cometary mass fluence and mean mass density along the Giotto trajectory was found to be 1.2 10−4 kg m−2 and 1.8 10−11 kg m−3, respectively. Within a time interval ± 45 s about closest approach, at least four well-established, sharply confined dust jets are distinguished, for which the characteristic geometries and production rates can be inferred. The total dust production rate is estimated to be 1.5 103 kg s−1. The comet’s jet structure derived from these Doppler data is shown to correlate with measurements on board Giotto.