The Friday File: Based on NASA’s Kepler Space Telescope exoplanet data set and stellar data from the European Space Agency, astronomers estimate that of the 100 billion stars in our galaxy, four billion are sunlike. Assuming 7% of those have an Earth sized rocky planet orbiting them at a distance allowing for liquid water, it means that conservatively there are 300 million potentially habitable planets, some just 20 light-years away!