Re: Drake increases estimate to 50K communicating E.T. civilizations

Rob Dekker wrote:

> Mercury is in tidal lock with the sun, but it is clearly outside (or
> actually way inside) the HZ for the sun. Interesting is that for Proxima,
> the HZ apparently overlaps with the tidal-lock zone...
> Is there a simple formula which expresses the 'tidal-lock-zone' of a
> particular star ?
> So, can we determine when a stars' HZ is totally within a tidal lock zone ?

That is an interesting notion, but I'm not sure we can draw any hard
borders around a star as to where a planet would become tidally locked.
Mercury is not *entirely* locked in that manner, as it still has an
axial rotation period which is different to its orbital revolution.
Much will also depend upon how much the planetary body departs from
being a complete sphere in its geometric profile; if there is a
significant "lobe" on one hemisphere of such a body, then that can
cause it to become tidally locked more readily and at a greater
distance (radius vector) than would otherwise be the case.

Unless someone here knows the dynamical intricacies more precisely and
can point out to the contrary, I don't think there is any *definite*
grounds for saying a planet in the HZ around Proxima Centauri is going
to be tidally locked for certain. There is a high *likelihood* of that
outcome, but it's not a foregone conclusion.

>
> Thus, if we assume for now that life (at least intelligent life) is unlikely
> inside the tidal lock zone, and unlikely outside the HZ, then there should
> be a large class of brown dwarfs that are unlikely to be able to have
> intelligent life planets...

I think brown dwarfs and many red dwarfs are automatically excluded
from the top of SETI lists on the grounds that they are too "exotic"
compared to more mainstream main sequence stars like the Sun?

>
> >
> > The second thing is, Proxima is what's known as a "flare star", so that
> > it doubles its luminosity every so often. That would render conditions
> > on the surface of any of its planets highly catastrophic to any life
> > managing to take a hold on it.
> >
>
> Variable stars, and variable circumstances are not necessarily excluding
> life.
> The best progress in evolution on planet Earth was made during the
> 'catastrophic' events like the KT boundary.
>
> So, I think that for life, it is more important how often these flare's
> happen than the simple
> fact that the do (happen).
> If there are violent outbreaks of 100% increase in radiation on the star
> every 100 years or more often, then I think the likelyhood of intelligent
> life developing there might be slim.
> Although I must say that we dont know much about this. Maybe life can
> built-in a protection system which allows easy survival for ANY frequently
> occurring event...
>
Where the seeds of life have already taken a firm *hold* and the
germination process has been triggered, the sprouting seedlings would
appear to be as solid as steel in their endurance of, and adapatability
to, harsh conditions. The planetary surface probably has to be
sufficiently *fertile* (i.e. with the right conditions, such as what
existed on the early Earth) for that to happen.

A lot of it really depends on whether we view life as having been
"created" or "seeded" here a long time ago. If it was "created" (out of
non-living compounds), then we're talking of some highly unique event
that probably does not recur with a greater probability than... say one
in a billion. In that case, life is indeed a very rare phenomena in the
universe and the nearest ETI civilisation may be... well, in the
Andromeda spiral, over 3 million light years away!

OTOH, if the seeds of life were already created - some time soon after
the birth of the universe - and are constantly drifting through space
in realtive abundance waiting for a *fertile* planetary shore on which
they can land and take a hold, then life is a lot more commonplace than
we think, and the nearest ETI civilisation may be just over on the
other side of the interstellar pond around Alpha Centauri.

The question is, and I've asked this often before without getting any
strong vibes either way, which is the popular view amongst the SETI
community here in the early years of the 21st century? Which was the
more common view back in the 1960s, when professor Frank Drake and
others started the SETI program? Is at (A) Created, or (B) Seeded?!

Cheers!
Abdul Ahad

.

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