NASA estimates 1 billion ‘Earths’ in our galaxy alone
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.
As Rachel Feltman reported Thursday, NASA’s Kepler Space Telescope has discovered a bunch of new planets, including one, Kepler 452b, that scientists described as the most Earth-like planet ever found outside our solar system. It’s something like 60 percent bigger in radius than the Earth (the exact size is hard to measure because it’s 1,400 light years away and cannot be directly imaged). But it’s probably rocky, and it's in the habitable zone of its parent star, which is like our own sun, a G-type “yellow dwarf” star. The parent star is 6 billion years old, roughly (everything’s “roughly,” unfortunately).
A few important reminders about our cousin Kepler 452b:
No one has seen it. Only Kepler has detected it — it’s too far away and dim to be detected with other instruments so far. So there’s a lot we don’t know about it. We don’t know for sure whether it’s rocky. We don’t know whether it has an atmosphere or water at the surface or anything like that. We’ve seen only the dimming of the starlight from the host star. The pattern of that dimming gives us a good measure of its orbital period (385 days) and, less precisely, its size. We’re not even sure of the exact size of the host star. These objects are very far away.
There is a video and more information at the site:
http://www.washingtonpost.com/news/s...r-galaxy-alone