Microwave detection of hydrogen sulphide and methanol in comet Austin (1989c1)

INFRARED and microwave spectroscopy can be used to identify and study the parent molecules directly sublimed from cometary nuclei. Here we report spectroscopic observations of comet Austin (1989c1) at millimetre wavelengths using the 30-m telescope of the Institut de Radio Astronomie Millimétrique (IRAM). We detected the rotational transitions of hydrogen cyanide and form-aldehyde, which were previously observed in comets Halley and Brorsen-Metcalf¹. In addition, we identified hydrogen sulphide and methanol, neither of which has previously been detected in a comet. The presence of hydrogen sulphide provides severe constraints on the formation of cometary nuclei, whereas that of methanol supports the hypothesis that cometary nuclei have retained, at least in part, some primitive material originating from the solar nebula.