From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Tue May 28 2002 - 11:36:38 MDT
On Tue, 28 May 2002, Robert J. Bradbury wrote:
> Even if one assumes the galactic "habitable" zone is only
> 1% of the galaxy, that means the number of "Earths" should
> be 240,000. Using the figure that 1/3 of these planets
> evolve life [2] implies there are ~80,000 life bearing planets
> in the galaxy. Of those planets, 75% of them (~60,000)
> should be older than the Earth on average by a billion years [4].
As pointed out to me offlist by Cole Kitchen, I miscomputed 1%
(that will teach me to do "advanced" math at 2 AM...).
The numbers should be 2.4 million, 800,000 and 600,000
respectively. (Or you could assume a galactic habitable
zone of 0.1% and use the numbers above). IMO, the galactic
habitable zone should be quite a bit bigger than 1%, but
a lot depends on how large the nearby supernova risks are.
Thanks to Cole for being so observant.
Robert
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