Kepler is an outer space telescope launched in 2009 that orbits the sun between Mars and Earth. It has been looking for exoplanets since that time which are planets that are outside our own solar system. As of February, 2011 Kepler had detected evidence of 1,235 such planets and more than 50 of these suspected exoplanets were considered to be in so called 'Goldilocks' zones. That is, located in manners that provide for their not being too hot nor too cold for life to exist on them. Based on this and other sample information that has been acquired so far scientists have extrapolated that there may be 50 billion exoplanets in the Milky Way of which 500 million may be capable of supporting life. The announcement was made on Saturday by Kepler science chief William Borucki at the American Association for the Advancement of Science in Washington D.C.

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And 500 million is just the estimated number of possibly life-bearing exoplanets for our very own Milky Way Galaxy.


From the "Atlas of the Universe" we find these estimates cited for galaxy numbers in the rest of the Universe:

* Number of galaxy groups in the visible universe = 25 billion
* Number of large galaxies in the visible universe = 350 billion
* Number of dwarf galaxies in the visible universe = 7 trillion
* Number of stars in the visible universe = 30 billion trillion  (3x10²²)


So, how very high are the chances of life of various sorts existing elsewhere, or of having existed elsewhere, in the Universe? 

The estimate of 50 billion planets in our galaxy seems to be a bit low considering that there is an estimated 200 billion+ stars in the galaxy without knowing how many red dwarfs there are - which could have habitable planets.  But 500 million is a pretty promising number for possible habitable planets.  I would speculate that the chance of life on at least a few is close to 100%.

And here we are, out on the ass end of nowhere.  Meh.
It may be that life is only possible out in the ass end of nowhere.  The radiation may be to great further in to allow life to emerge.

Good point, yeah.


Well, except you'd think that larger suns would have a larger Goldilocks zone, further out from the primary ... unless there's something different about the radiation of those stars that makes them bad, even in the Goldilocks zone ...



I don't think we can say it is absolutely impossible for life to have evolved somewhere to live in non-Goldilocks conditions but we have no empirical evidence to suggest that it ever has. We have life on earth from which to conclude that life might exist in Goldilocks conditions so we consider exoplanets in Goldilocks zones to be more credible candidates for supporting life.

The hard line for life "as we know it" to exist is the range between 0 and 100 degrees centigrade.  Our biological system requires liquid water.  Actually though, the higher end of the range is a bit tighter than that.  DNA uncoils and stops functioning properly, well below the boiling point of water.


I saw the exact number in an article discussing how DNA testing works, explaining how DNA unzips at a certain temperature, if it's a perfectly matched set, but unzips at a lower temperature, the more unmatched genes there are on either side of the helix.  This is how we figure out what percentage of genes two different species share.  I think it was linked off of some post on Atheist Nexus, but I can't remember where it was from.

"as we know it"


All life in the universe might not be as we know it.

Well yeah.  We're just starting our search for DNA-based life, for whatever reason.
There is the possibility  a planet outside of the goldilocks zone that has sufficient internal heat to support life  - but not to far out.


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