How big is the universe? No one really knows, but since we are in just one Orion spur of the arm of Sagittarius in one galaxy, and there are an unknown number of galaxies, it's big. So big our galaxy alone could have 6,000,000,000 planets like ours,
according to a new estimate.
To be a potential planet like Earth, the new model estimating the number of planets like ours must be rocky, roughly Earth-sized and orbiting Sol-like (G-type) stars. It also has to orbit in the habitable zones of its star, which is the range of distances from a star in which a rocky planet could host liquid water on its surface.