Abstract

The relation between the mass of a cometary nucleus, its gas production curve, the mean outflow velocity, and the nongravitational delay of the comet is discussed, emphasizing the properties of gaseous outflow from comet Halley. The importance of knowledge about the rotational state of the nucleus is stressed, and it is argued that the likely wobbling of the P/Halley nucleus greatly simplifies the problem. The observational data on the H₂O production curve of comet Halley is discussed with emphasis on the discrepancy between Ly-ga and near-IR H₂O data on the one hand and data from OH and O¹D on the other. It is shown that roughly 75-80% of the nongravitational delay of comet Halley should arise from the perihelion asymmetry of the H₂O production curve, and thus the mass is sensitive to the choice of this curve. Values of 1.3 and 3.1.10¹⁴ kg are found, corresponding to densities of 0.28 and 0.65 g/cm³, and preference is given to the lower values based on OH data. Other sources of uncertainty amount to +/-30%. The remaining active lifetime of comet Halley is 500-1000 revolutions assuming that the nucleus does not become sealed off by the surface dust layer. This is probably smaller than the past number of apparitions, so the present nucleus may differ drastically from the original one.