[extropy-chat] Most star systems are single

[Robert Bradbury]

On 5/27/06, Amara Graps <amara at amara.com> wrote:

> 1) The 'habitable zone' is close in and narrow : 0.2 to 0.5 A.U. where
> the A.U. is the distance to the M-class main sequence star.


Amara, as I'm sure you are aware (as should be Spike), the "habitable zone"
is only a relevant concept for "primitive" life that requires a solvent (e.g.
water) to allow significantly increased probabilities that simple molecules
will run into each other and form more complex molecules.  (Molecular
evolution occurs at a much slower pace in solids and complex molecules (at
least those used by life on Earth) have much shorter lifetimes at higher
temperatures).  Once you have non-solvent based "life" forms the range of
natural "habitable zones" expands significantly.  Once you have "intelligent
life" there is always a chance that they will tailor the sun, planet, or
other environment suitably to sustain the temperatures they happen to
prefer.  There is no problem having liquid water at Pluto's distance from a
star if one is willing to dedicate enough matter to attaining those
temperatures.

Given that there are many Earths in our galaxy which were probably much
older than ours it is certainly reasonable that more evolved civilizations
may use M-class star systems as fuel depots, observation outposts, light
metal manufacturing reactors, or a whole host of other activities which we
may have a hard time imagining at this time.

So discussions of the "classic" (primitive life) habitable zones should be
balanced with the concept that such zones are but a small fraction of the
total habitable zones in the galaxy.  In fact the entire volume of the
galaxy, including surrounding intergalactic space, excepting perhaps regions
extremely close to stars (constant temperatures greater than the maximal
melting point of most materials) or places where there is a high constant or
near term future high energy radiation flux (black holes, pending
supernovas, etc.) should be considered to be the real habitable zone.

Robert
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