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 ----------------------------------------------------------------- gopher://quux.org/ conversion by John Goerzen of http://communication.ucsd.edu/A-News/ This Usenet Oldnews Archive article may be copied and distributed freely, provided: 1. There is no money collected for the text(s) of the articles. 2. The following notice remains appended to each copy: The Usenet Oldnews Archive: Compilation Copyright (C) 1981, 1996 Bruce Jones, Henry Spencer, David Wiseman.