Activity of comet Halley observed in the ultraviolet


  • E. Kaneda,

  • K. Hirao,

  • M. Shimizu,

  • O. Ashihara


The time variation of the water production rate of comet Halley during this apparition has been deduced from observations of the Ultraviolet Imager on board Suisei. The preperihelion production rates were a factor of 2 ∼ 3 smaller than postperihelion rates, suggesting a postperihelion heating of the cometary nucleus. Some fine intensity structure in the Lyman alpha photometry data taken at encounter, which indicates spatial variation of the atomic hydrogen density in the coma, may correspond to shell structures in the Lyman alpha images so far obtained and is ascribed to the presence of a hydrogen source other than water in the cometary gas or dust particles. The velocity of these hydrogen atoms is estimated to be about 11 km s−1.