The Outburst of Comet p/ Halley on 1985DEC12

A strong outburst with a southward jet was found during 9^h07^m to 12^h29^m UT on December 12, 1985 while the authors were observing the near nucleus region of comet P/Halley. The projected expansion velocity is estimated to be 0.3±0.1 km s^-1 and the dust number density is 9 times as large as that in the coma background, assuming the jet cone angle is 30°. As the width of the jet in the C₂ emission band is 10% broader than that in white light, it can be concluded that the C₂ molecules are created from some parent body in the ejected matter.