Astrobiology has entered an exciting new phase in recent decades. Since the 1990s, but accelerating in recent years, researchers have begun confirming the existence of exoplanets – that is, planets outside our own solar system – and studying their properties. We now know that planets are common, and a sizeable fraction orbit in the habitable zone of their parent star – suggesting they could have the conditions to sustain biological life.

Studies have also revealed entirely new classes of worlds we had no idea could exist. Hycean planets are unknown in our solar system, and are possibly some of the strangest planets discovered to date. They may be ocean-covered worlds with hydrogen-rich atmospheres and, as such, are promising candidates for the detection of biosignature gases – chemical products we associate with living things. But this is not the only possibility. Their discovery has expanded our concept of habitability and challenged our notions of what kinds of environments can sustain life – both as we know it and as we might not.

Against this backdrop, the recent James Webb space telescope observations of K2-18b, a planet orbiting a red dwarf star 124 light years from Earth, stand out. The latest study, published last week in Astrophysical Journal Letters by a team led by Nikku Madhusudhan, reports a tentative detection of dimethyl sulphide (DMS) or dimethyl disulphide (DMDS), which are gases that we know to be produced by living organisms. While the media tends to focus on the exciting possibility of the

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