section_path: Habitability
section_name: Habitability
paragraph_text: Habitability
  
  Incoming stellar radiation amounts to 1,368 +114 −107 W / m 2, similar to the average insolation Earth receives. K2-18b is located within or just slightly inside the habitable zone of its star, – it may be close to but fall short of the runaway greenhouse threshold – and its temperature in the absence of a greenhouse is about 250 K (−23 °C; −10 °F) to 300 K (27 °C; 80 °F). Whether the planet is actually habitable depends on the nature of the atmosphere and the albedo of clouds and hazes; the deeper layers of the atmosphere may be too hot, while the water-containing layers might or might not have temperatures and pressures suitable for the development of life.
  
  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. According to Madhusudhan et al., several of these markers could be detected by the James Webb Space Telescope after a reasonable number of observations.