Dual-frequency Vega radio sounding of Comet Halley

Radiophysical effects observed by Vega 1 and 2 as they passed through Comet Halley are presented and analyzed. Variations in the amplitude and frequency of the centimeter and decimeter signals, and the normalized phase difference of the two coherent signals are examined. From the Vega 1 data obtained on March 6, 1986, it is observed that the two signals began to rise in frequency as the spacecraft approached the comet; however, no frequency shift was detected by Vega 2 on March 9, 1986. A peak electron column density of 7.5 x 10 to the 12th/sq cm and a local electron space density of 2000-3000/cu cm were derived from the Vega 1 normalized phase differential data, and from the Vega 2 data, the peak electron column density was estimated as 3.5 x 10 to the 12th/sq cm and the local electron space density as 1000-2000/cu cm. 5 references.