Water-production rates of comet 46P as a function of time from perihelion during 1991 (orange), 1997 (black), 2008 (blue), and 2018 (in red) apparitions. Fink et al. (1998) derived the water-production rate from the [OI](¹D) forbidden line doublet emission in the optical, Bertaux et al. (1999) values were derived from the H Ly-α emission observed by the SWAN instrument on board SOHO and Crovisier et al. (2002) values were derived from the OH emission observed at the radio wavelengths.