Asri-unix.942
net.space
utcsrgv!utzoo!decvax!ucbvax!C70:sri-unix!Lynn.ES@PARC-MAXC
Wed Mar 10 10:01:22 1982
Re: life is dangerous on planets
As the space junk gets swept up by the planets, collisions are getting orders of
magnitude rarer than they were in the early existence of the planets. Assuming
our history is typical of a planetary system, it seems that life gets reasonably
safe on planets eventually anyway. The numbers I've seen on collision
frequency imply that the 65 million years since the supposed collision that wiped
out the dinosaurs is not a particularly long interval.
Given the number of stars in the milky way, its size, and the assumption that
many of its stars are double or worse, the average spacing between star systems
(system = double or single or whatever) is in the range of 8 or 10 light years.
Of course no star will be exactly equal distant from its neighbors in all
directions, so our distance of 4 light years for the closest direction is quite
average. This average holds roughly over the outer parts of the galaxy, but is
not valid at all in the areas much closer to the center of a galaxy than we are.
There the density gets much higher, probably orders of magnitude higher.
Speculations are that stable planetary systems would not last long in the center
of a galaxy.
/Don Lynn
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