section_path: Host star
section_name: Host star
paragraph_text: Host star
  
  K2-18 is an M dwarf of the spectral class M3V in the constellation Leo, 38.025 ± 0.079 parsecs (124.02 ± 0.26 ly) distant. The star is colder and smaller than the Sun, having a temperature of 3,457 K (3,184 °C; 5,763 °F) and a radius 45% of the Sun's, and is not visible to the naked eye from the Earth. The star is 2.4 ± 0.6 billion years old and displays moderate stellar activity, but whether it has star spots, which would tend to create false signals when a planet crosses them, is unclear. K2-18 has an additional planet inside of K2-18b's orbit, K2-18c, which may interact with K2-18b through tides.
  
  It is estimated that up to 80% of all M dwarf stars have planets in their habitable zones, including the stars LHS 1140, Proxima Centauri and TRAPPIST-1. The small mass, size and low temperatures of these stars and frequent orbits of the planets make it easier to characterize the planets. On the other hand, the low luminosity of the stars can make spectroscopic analysis of planets difficult, and the stars are frequently active with flares and inhomogeneous stellar surfaces (faculae and starspots), which can produce erroneous spectral signals when investigating a planet.