The Habitable Zones around stars with different surface temperatures. The figure also shows an artist’s rendering of the planetary candidates and confirmed Kepler planets that are smaller than twice the size of Earth. For comparison, Venus, Earth, and Mars are also shown. The colored curves delineate various possible inner and outer limits for the Habitable Zone.
The red and yellow curves, respectively, show inner limits based on the empirical observation that the surface of Venus has been dry for at least a billion years, and the distance at which the oceans evaporate entirely. The blue and orange curves are outer limits, where the CO2 greenhouse effect maximizes (blue), and based on the observation that Mars appears to have been habitable 3.8 billion years ago when the solar luminosity was 25% lower (orange).
Web: University of Hawaii