There are a billion Earths in this galaxy, roughly speaking. Not a million. A billion. We’re talking 1 billion rocky planets that are approximately the size of the Earth and are orbiting familiar-looking yellow-sunshine stars in the orbital “habitable zone” where water could be liquid at the surface.
That’s a billion planets where human beings, or their genetically modified descendants, as well as their dogs and cats and tomato plants and crepe myrtle trees and ladybugs and earthworms and whatnot, could plausibly live.
The estimate comes from NASA scientist Natalie Batalha. Let’s go through some background information to see how she got to that number. Thank you, Dr. Batalha! Keep in mind, she is using conservative estimates. So 1 billion may be a little low.
Before we make plans for colonizing these other Earths, we should pause for a second to note that there are two "Earth-like" planets orbiting our own sun and much, much closer to home than any of these extrasolar planets. Getting Venus in shape for habitability would be a terraforming challenge of the first order. Mars is potentially more congenial, but still an unpleasant place by our standards. Before we colonize Mars, we'll probably colonize the bottom of our shallow seas. Your scribbler will avoid going into a full rant about people who think there's a do-over in space for when we ruin our own planet.
