Sulphur is chemically versatile and ubiquitous, and important in both planetary and astrochemical processes. Compared to its cosmic abundance, it appears to be significantly depleted in dense interstellar regions -- a phenomenon that is the subject of ongoing research. Comets, which retain material from the early Solar System, provide a valuable record for assessing sulphur reservoirs and their isotopic compositions. Comet 67P/Churyumov–Gerasimenko was particularly suitable for in situ investigation. This study aims to determine the 34 S/³2S isotopic ratios of CS₂ in comet 67P/Churyumov–Gerasimenko and to investigate if the CS₂ isotopologue double ratio, ¹2C³4S₂/¹2C³4S³2S-to-¹2C³4S³2S/¹2C³2S₂, is consistent with the statistically expected value. We analysed high-resolution spectra acquired by the ROSINA Double Focusing Mass Spectrometer (ROSINA/DFMS) in March 2016, when the Rosetta spacecraft was within 17 km of the nucleus and the CS₂ signal was high. Three CS₂ isotopologues, 12 C³2S₂, ¹2C³4S³2S, and ¹2C³4S₂, were used to derive three ³4S/^ 32 S isotopic ratios. We report on the first detection of the doubly heavy isotopologue 12 C³4S₂ in a comet. All three derived ³4S/³2S ratios yield consistent results, with δ³4S values ranging from -69. 91 to -5. 49 S. In contrast to the strong mass-dependent fractionation in water isotopologues measured on 67P -- a D₂O/HDO-to-HDO/H₂O ratio of 17, which is far above the equilibrium value of 0. 25 -- our CS₂ isotopologue double ratio yields 0. 2377 These are within 1 to 2σ of the Vienna-Canyon Diablo Troilite (V-CDT) standard, indicating at most a minor depletion in 34 consistent within 1σ of the statistically expected value of 0. 25.
Doriot et al. (Wed,) studied this question.