Activity and the Rotation Period of Comet Hyakutake (1996 B2)

Narrowband photometry of Comet Hyakutake (1996 B2) revealed periodic variability in the production of dust and gas during the comet's close approach to Earth in March 1996. The photometry alone was insufficient to unambiguously discriminate among several possible periods, but a unique period determination was possible by utilizing repeating morphological features in CCD images obtained simultaneously with the photometry on the nights of March 23-25. In particular, a large puff or blob of material was seen to be released in the sunward direction every 6.23 ± 0.03 h. This periodic release of material, presumably from a single dominant active region on the surface, was the source of the observed lightcurve variations. A second, much smaller morphological feature also repeats each cycle, confirming the value of 6.23 h for Hyakutake's synodic rotational period.