Distribution of super-Earth exoplanets
Super-Earth exoplanets with known radius and mass (1 < Mplanet ≤ 10 MEarth or Rplanet ≤ 2 REarth) for different host star masses, and with respect to the position of the habitable zone shown in green (Rauer et al. 2014). Earth, Venus and Mercury are shown for reference. The habitable zone, defined as the area around a star where water may be in liquid form on the surface of an orbiting planet, is empty except for planets around very cool stars. The main objective of PLATO is to populate this diagram by determining the bulk properties and ages of small planets up to the habitable zone of Sun-like stars.