Comet Halley's nucleus: A physical interpretation

The nucleus of comet Halley was the first to be detected and observed by cameras on board spacecraft during the fly-bys in 1986. The interpretation of both these observations and of the results from other experiments as well as many subsequent corroborative measurements of comet Halley and of other comets are reviewed. Cometary nuclei are relatively large and non-spherical in shape. They show activity only on small fractions of their surfaces. The physical processes leading to such heterogeneous surfaces are not yet understood. Our present concept of cometary nuclei and their formation are discussed. Open questions and problems are addressed. (C) 1997 COSPAR.