Is there really life on planet K2-18b? We can’t rule it out, but some key questions must be answered | Nathalie Cabrol

A new study of a sphere orbiting a red dwarf star 124 light years from Earth is raising hopes. Here's why the evidence is inconclusive

• Nathalie Cabrol is director of the Carl Sagan Center at the Seti Institute

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.

Nathalie Cabrol is director of the Carl Sagan Center at the Seti Institute, and author of The Secret Life of the Universe: An Astrobiologist's Search for the Origins and Frontiers of Life