Comet 46P/Wirtanen, the target of the Rosetta mission

We present a summary of the observational data on periodic comet 46P/Wirtanen, emphasizing the recent estimates of H2O production rate from narrow-band photometry and CCD imaging with ensuing estimates of the photometric cross-section of the nucleus. A discussion of the consequences of these data for our understanding of the physical state of the nucleus is performed, from which it is deduced that the nucleus may be in a state of very high activity. The possibility of "hyper-activity" is also considered, and we suggest that fragmentation of the surface layers may occur near perihelion, leading to sublimation from short-lived, icy fragments in addition to the nuclear surface. (C) 1998 COSPAR. Published by Elsevier Science Ltd.