3. Kepler-22b While Kepler-22b is bigger than Earth, it circles a star that is quite close in size and temperature to Earth's sun. Kepler-22b is 2.4 times Earth's size and, assuming its greenhouse effect is similar to Earth's, has an estimated surface temperature of 72 degrees Fahrenheit (22 degrees Celsius.) Its star system is about 600 light-years away from Earth's sun, in the constellation Cygnus.