It is estimated that there are millions of Earth-like planets in our Galaxy. However, most of these are out of our observational abilities for the coming decades, and probably many centuries. Only a small fraction of these planets, the ones that transit their star, are good enough for better characterization and to confirm their potential for life. This result suggests that there are over 8,500 transiting very Earth-like planets within reach of NASA Kepler-like missions, assuming the Kepler field is representative of all the sky. This sample is enough to occupy astronomers for many years.
The image above shows the size and scale of the Kepler-452 system compared alongside the Kepler-186 system and the solar system. Kepler-186 is a miniature solar system that would fit entirely inside the orbit of Mercury. The habitable zone of Kepler-186 is very small compared to that of Kepler-452 or the sun because it is a much smaller, cooler star. The size and extent of the habitable zone of Kepler-452 is nearly the same as that of the sun, but is slightly bigger because Kepler-452 is somewhat older, bigger and brighter. The size of the orbit of Kepler-452b is nearly the same as that of the Earth at 1.05 AU. Kepler-452b orbits its star once every 385 days.
The Daily Galaxy via NASA/Kepler Mission and University of Puerto Rico
Image Credits: NASA Ames/JPL-CalTech/R. Hurt and NASA Ames/W. Stenzel