Letter to the Editor Radio detection of ammonia in comet Hale-Bopp

Radio emission from ammonia, a suspected parent molecule in comets, was detected from comet Hale-Bopp near its perihelion passage with the 100-m Effelsberg Radio Telescope. Signals from the five lowest metastable inversion transitions of NH3 were obtained to derive a rotational temperature of 104±30 K, assumed to be representative of the kinetic temperature in the comet’s inner coma (R < 5000 km). The ammonia production rate at perihelion is calculated from these observations to be 6.6±1.3× 1028 s−1 (almost two tons of ammonia per second). Compared with independently determined water production rates near perihelion, the implied ammonia abundance ratio to water is in the range 1.0–1.8%.