The Kepler-186 planetary system, reimagined with a hypothetical sixth planet.  The top part shows a view of the planets' orbits.  The habitable zone is shaded.  The bottom part compares the amount of energy received by each planet with the energy received by the Solar System's planets.  The hypothetical planet -- at its most likely location --  receives just slightly less energy from its star than the Earth does from the Sun, placing it toward the inner edge of the habitable zone.