Stars, galaxies, and planets

NASA estimates that the Milky Way contains roughly 100–400 billion stars. The number of galaxies in the observable Universe is estimated at about 2 trillion, an extrapolation rather than a census of every galaxy. Studies estimate at least 100 billion planets overall in our galaxy; a separate estimate based on Kepler data puts the number of rocky worlds in the liquid-water habitable zone at at least 300 million. “Earth-like” does not mean life has been found there.