There have been reports in the press over the last 24hrs of dimethyl sulphide, CH₃-S-CH₃, DMS, being found in the atmosphere of an exoplanet, by the James Webb telescope. The planet is K2-18b, orbiting the "cool dwarf" star K2-18 in Leo, and 120 light years from Earth. It is assessed as being in the habitable zone for that solar system. The significance of DMS is that, on Earth, it is only synthesised biologically, mainly by phytoplankton. Trying to find something more substantial than news bulletins, I came across this briefing from NASA: https://www.nasa.gov/goddard/2023/webb-discovers-methane-carbon-dioxide-in-atmosphere-of-k2-18b Interestingly, this leads with the identification of CO₂ and CH₄, rather than DMS. It stresses that the identification of DMS is only tentative and remains to be confirmed. However the low level of NH₃ is considered significant, possibly indicating oceans of liquid water. I presume that would be because ammonia is very water-soluble. So anyway, one to watch as a good candidate for extraterrestrial life of some kind.
It will be frustrating though, since even if DMS is confirmed it won’t be remotely conclusive. I expect the chemists are even now thinking about inorganic synthesis routes for it.
