>No.  I don't think a similar-sized sun would be a necessity, unless you're
>being *very, very* lax with "similar", nor a "orbit
sized" life zone.  Just
>the temperature zone is likely, such that liquid water needs to exist
>somewhere on the planet.  Of course, I don't *absolutely* rule out some
>sort
>of different life form in other unknowable environments, but that would
>be
>far less likely, IMHO.   Regards, Brett.

Well lets go further.
The strength of UV varies.
Certain distances between the star and its planet may be too weak to break the
bonds or form the monomers, etc. that seem to lead to the origin, while certain
shorter distance may be too strong.
This is something that would be an important aspect, IF I am correct in
suggesting that the sun/UV cycle initiated the origin and powered it through
every step.
It also would further restrict size, distance etc.

Overall I would say this - the fit between star and planet must be such that
there is a reasonably constant cyclic temperature zone that allows for liquid
water, and a similar reducing atmosphere as earth probably had.
Its size probably has to allow for volcanic activity - the source of earth's
water,  atmosphere etc.
(And PERHAPS having a Moon that is more nearly the size of earth than any
planet/moon in the system, is an important fact too. Its close proximity after
the planetoid collision that formed it; set up a much shorter day of something
like 5 hours of sun, then 5 hours of night. Perhaps a spin that is much less is
too slow to
power the necessary steps of life, and a spin too fast is much more than that
necessary to form and support life.

And lets' add this point. IF the star is much much bigger
than the sun, it will burn out as quickly as in a billion years. Even if life
began on a planet - it is highly unlikely that it would  progress beyond  a
simple bacteria like single cell life form. So even if there is life, it would
never have the chance to be intelligent life (and we may have had to have that
coment taking out the dinos before we tree swingers had a chance)

More and more restrictions to consider in the origin.

Tom
---
þ RIMEGate(tm)/RGXPost V1.14 at BBSWORLD * Info{at}bbsworld.com

---
 * RIMEGate(tm)V10.2áÿ* RelayNet(tm) NNTP Gateway * MoonDog BBS
 * RgateImp.MoonDog.BBS at 10/1/04 5:29:37 PM