View Full Version : 17B Earths in the galaxy!

2013-Jan-08, 05:44 PM

"there are 17 billion other Earths in our galaxy, the Milky Way."

and that's only this galaxy. How many there are in the entire universe?!

2013-Jan-08, 05:54 PM
How narrowly you define Earth-like planet will raise or lower that number quite a bit. I'm willing to commit to there being many planets with atmosphere, exposed liquid water, and exposed land, but I wouldn't give the number two significant digits.

2013-Jan-08, 06:15 PM
If Earth was in the same orbits as most of these discoveries so far, it would not be life-supporting. We still have a only a small sample to guess what the rest of the galaxy has. Location in the galaxy probably also plays a part, I think that's one of the reasons why Kepler sampled the area that it did.

A more accurate number would how much percent of that 17% are actually habitable, and that we still don't know, but it drops the overall number.

2013-Jan-08, 10:09 PM
I agree 17 billion is at least a little optimistc, as 100 day orbits of G stars will be too hot unless they are tide locked to their star, then the cooler twilight band will not have enough light for photo synthesis. 100 day orbits are possibly just right for K stars, but cold as Mars for hotter M stars, some of which have more hazardos CME and sunspots than our Sun. Also the orbits need to be reasonably close to circular or golilocks band is even narrower. It is thought that warm planets close to the dimest M stars will be tide locked which may mean most of the water is sequestered in a giant ice cap on the dark side = likely not a good place for life to start. Some sections of our are galaxy are likely much less safe for life than a radius of 1000 parsec around Earth. Likely very advanced beings can live almost anywhere, so perhaps that is 17% or 17 billion livable planets. Neil

2013-Jan-09, 03:19 PM
So again we realize that Gene Roddenberry was right about EM-class planets....