Maria Drozdovskaya (Center for Space and Habitability (CSH), Universität Bern) 

The recently discovered semi-refractory ammonium salts are thought to be harboring the missing nitrogen reservoir in comets. Upon thermal desorption, ammonium salts decompose into ammonia (NH3) and a corresponding acid. Consequently, the abundance of NH3 relative to the dominant cometary volatile, H2O, is expected to increase with decreasing heliocentric distance. We have constrained the NH3/H2O ratio in comet C/2020 F3 (NEOWISE) during its July 2020 passage at 0.7 au from the Sun. The comet was monitored for 2 months with the Nançay Radio Telescope and observed on two dates with the Green Bank Telescope. The obtained NH3/H2O ratio is a factor of a few lower than measurements for other comets at such heliocentric distances. It is hypothesized that the abundance of NH3 may vary strongly with time, depending on outbursts and the amount of small, hot, dry dust in the coma.