Almost Earth Revisited

Last week in my regular blog I wrote that we shouldn’t expect astronomers to find an Earth-sized planet out there very soon.  I may have spoken too soon.  After that post, two articles appeared on Yahoo News about that very subject.  One story, from Space.com, reported that the NASA Kepler astronomical satellite telescope had found in the last year over 800 new planets orbiting stars outside out solar system, and 104 of them could be potentially habitable.  Only ten of them, though, are the size of Earth.  But keep in mind that we are still in the early stages of examining these planets, and just because they are Earth-sized doesn’t mean they have life on them.  Many other factors will determine the presence of life, and it will be a while before a complete determination is made just which ones are potential life-possessing planets.  It will take time.

The second article, from the Associated Press, reported that there may be as many as 8.8 billion Earth-sized, just right planets in our galaxy.  That takes into account only planets that orbit stars like our sun, exist in the habitable zone where life as we know it could develop, and are about the size of Earth.  Out of all the planets in the Milky Way Galaxy, those conditions narrow the field quite a bit, but still take into account, by their estimation, several billion planets.  At first I thought that number sounded high, but I realized almost immediately it wasn’t.  Consider the Kepler spacecraft I mentioned above.  It has found thousands of planets, yet it examines only a tiny portion of the sky.  By expanding that potential over the whole sky and throughout the entire galaxy, the number of planets, and even the number of potential life-possessing planets, becomes staggering.  That’s where they got the number 8.8 billion.  That’s an 88 followed by eight zeros.  Now, even though the conditions for life existing on a planet’s surface are extremely narrow and stringent and will eliminate most of those 8.8 billion, the chances should still be relatively high that somewhere within those remaining planets life has evolved.  Taking it out to the point of intelligent life would reduce that number even further, but it’s still possible.  And taking it out to intelligent life capable of spaceflight would reduce the numbers even further.  In fact, I suspect that the number of planets having intelligent life capable of spaceflight might be as low as 80, or even 8, not counting our own.  Some of those worlds where spaceflight is possible may be on the other side of the galaxy where we can’t see them.  In any event, finding life of any sort will be a challenge, and as I said last week, it will take time.  Get used to it.

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