Science

Incoming stellar radiation amounts to 1368+114
−107 W/m2, similar to the average insolation Earth receives.[7] K2-18b is located within or just slightly inside the habitable zone of its star,[62] – it may be close to[63] but fall short the runaway greenhouse threshold[64] – and its equilibrium temperature is about 250 K (−23 °C; −10 °F) to 300 K (27 °C; 80 °F).[15] Whether the planet is actually habitable depends on the nature of the envelope;[30] the deeper layers of the atmosphere may be too hot,[34] while the water-containing layers might have temperatures and pressures suitable for the development of life.[25]

Microorganisms from Earth can survive in hydrogen-rich atmospheres, illustrating that hydrogen is no impediment to life. However, a number of biosignature gases used to identify the presence of life are not reliable indicators when found in a hydrogen-rich atmosphere, thus different markers would be needed to identify biological activity at K2-18b.[65] According to Madhusudhan et al., several of these markers could be detected by the James Webb Space Telescope after a reasonable number of observations.[66]