Comet Halley’s outburst

It is suggested that the outburst suffered by Comet Halley (1986 III) in early February 1991, was caused by the ejection from the nucleus of $$1.4 \times 10^{13}\enspace \text g$$ of dust, this being about 0.02 per cent of the cometary mass. The energy required was in the range $$2 \times 10^{19}$ to $$2 \times 10^{23}$ erg. The most likely source of this energy was an impact, with a member of an outer asteroid belt, the impacting object having a diameter of between about 2.6 and 60 m.