C/2020 F3 (NEOWISE) was discovered in images from the Near Earth Object program of the Wide-Field Infrared Survey Explorer (NEOWISE) taken on 27 March 2020. The Solar Wind ANisotropies (SWAN) camera on the Solar and Heliospheric Observatory (SOHO) spacecraft, located in a halo orbit around the Earth-Sun L1 Lagrange point, makes daily full-sky images of hydrogen Lyman-alpha. Water production rates were determined from the SWAN hydrogen Lyman-alpha brightness and its spatial distribution. The water production rate, varying with the heliocentric distance, r, as ~r-3.4 both before and after perihelion as well as its inbound semi-major axis of 270 AU is consistent with the comet not being dynamically new and having been previously through the planetary region of the solar system on one or more past apparitions. Water production rates as large as 4.45×1030 s-1 were found shortly after perihelion once the comet was outside the solar avoidance area of SWAN when the comet was 0.324 AU from the Sun. As of submission of this abstract the variation of water production rate is somewhat higher after perihelion than before.
Support is acknowledged from NASA grant 80NSSC18K1005 from the Solar System Observations Program, the Finnish Meteorological Institute (FMI), and from CNRS and CNES.