From: Thomas Buckner (tcbevolver@yahoo.com)
Date: Thu Sep 30 2004 - 15:23:23 MDT
--- Dani Eder <danielravennest@yahoo.com> wrote:
> Re: Fermi Paradox
> > >Possibility: we're really the first.
> >
> > Given the extremely unfriendly planetary
> systems we
> > have seen so far, this
> > looks increasingly likely.
> >
>
> The extrasolar planets we have found so far are
> a biased sample due to the way we have been
> looking
> for them. We don't have much data relevant to
> addressing the 'intelligent life is rare'
> answer
> to the Fermi Paradox yet, but it is finally
> coming
> in.
>
> The current methods used to find extrasolar
> planets
> involve looking for a wobble in the star or a
> dimming in the star's light. Astrometry
> measures
> the side-to-side wobble of a star under the
> gravity
> of a planet or brown dwarf. Spectroscopy
> measures
> the doppler shift of the star's spectral lines
> towards and away from us from the same cause.
>
> Both methods are biased towards heavy objects.
> Astrometry is also biased to objects in wide
> orbits,
> since it produces larger wobbles in the star.
> Spectroscopy is biased to small orbits, since
> it
> produces larger doppler shifts in the star.
> Neither
> method is capable of locating earth-mass
> objects
> at present.
>
> The third method involves looking for the
> dimming
> of a star's light as a planet transits in front
> of
> it. Transits are rare, since the planet's
> orbit
> has to be aligned edge on from our point of
> view,
> and even then they occur on the order of 1/1000
> of
> the orbit period. Therefore you have to
> monitor
> a lot of stars for extended periods to find
> one.
>
> Automated telescopes with big CCDs have only
> recently
> (a few years) been able to do this kind of
> search,
> and results are just starting to come in.
>
> The fourth and most obvious method, direct
> observation
> via imaging, is very difficult due to the glare
> of
> the star. There is one disputed sighting of a
> planet visually. There are telescopes and
> missions
> planned in the next ten years or so that should
> be able to succeed with visual searches.
>
> There is a well known size distribution law in
> astronomical circles both for stars and for
> smaller
> objects in our solar system. It is observed
> that
> the number of objects goes as some power
> (around
> -2.5 if I remember right) of the diameter or
> mass.
> That means there are lots more small objects
> than
> large ones. The hundred or so extrasolar
> planets
> found so far, when you correct for observation
> bias and allow for the still large
> uncertainties
> in their sizes, seem to be following a similar
> law.
>
> This is encouraging, since it implies for every
> planet we are finding in the 0.3-80 Jupiter
> mass
> range, there should be multiple planets in the
> 0.0003-0.03 Jupiter (0.1 to 10 Earth) mass
> range.
>
> In the next 5-10 years we should be able to
> assign
> realistic values to the term f(p) [fraction of
> stars with planets] in the Drake Equation. The
> next term, [fraction of planets that can
> support
> life], will take a little longer to move from
> the stage of 'guess with no data' to 'estimate
> with
> some data'.
>
> Daniel
>
All perfectly reasonable. However, I look at
minimum times to evolve any sort of intelligent
technological society and (as I understand it)
things have moved about as fast as they can.
There's the time for the universe to cool and
form atoms (mostly hydrogen-helium) then the time
for big stars to cook up heavy elements and
supernova, then time for new stars/planets to
form, and only then does life as we know it
begin. Assume Earth is typical, single-celled
organisms were all you'd find for 90% of the time
since Earth cooled from a magma ball, and since
Cambrian it's been accelerating complexity here.
But if our intelligent society went bust, another
might not evolve for ?100m years perhaps. Recall
the Sun is already half through its useful cycle,
so really it's probably not hard for life on a
given planet to run out of time.
Bottom line: if not the first, we are still
early, cosmically speaking.
BTW I agree with all comments on radio
transmissions. We now see heavy use of
short-range encrypted wi-fi and other very local,
low-power applications. Many high-power
applications such as radar might be obviated by
'smart dust' which could track anything of
interest in the atmosphere. High-powered radio
transmissions might be confined largely to power
transmission. All these considerations suggest
that 'mature' radio technology is hard to detect
at cosmic distances. 30 years ago it was assumed
a growing civ would expend vast energies
communicating its presence via radio. Now seems
unlikely: inefficient even if one did wish to
reveal one's location. Sending out small craft
with data has been suggested instead.
Tom Buckner
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