There are more planets than there are stars, and at least a quarter are Earth-size planets in their star’s so-called habitable zone, where conditions are neither too hot nor too cold for life. With a minimum of 100 billion stars in the Milky Way, that means there are at least 25 billion places where life could conceivably take hold in our galaxy alone, and our galaxy is one among trillions. **
** National Geographic 03-2019 We are not alone / Search for life