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Re: Drakes Equation



At 11:46 PM 8/26/95 -0400, GSP1954@aol.com wrote:
>Despite searching for gas giants with Hubble etc around nearest 100 stars, no
>giant planets have been spotted.

      Using our curent technology to detect planetary bodies orbiting other
stellar systems is hellishly difficult. Planets are dark, cool, low-mass
bodies compared to the stars they orbit. It's much too early to suggest
jovian planets are rare. Our own solar system sports two full-fledged jovian
bodies (Jupiter and Saturn) and two sub-jovian examples (Uranus and Neptune).

>Also, super computer simulations of forming
>solar systems easily produce inner rocky planets, but not gas giants.

     I don't recall seeing these data. Please cite the source.

>Finally, a comet from another star's Oort cloud has never been seen around
>these here parts, although by now they should have if gas giants that clear
>inner solar systems of comets are common.

     The Oort cloud of cometary objects orbits the sun at distances far from
the inner solar system. Objects flung from the cloud most likely would have
been perturbed by encounters with the gravitational fields of nearby passing
stars (or stars the sun overtakes), not by planetary bodies closer to the
parent star. Judging from the scant historical data at hand (the nature of
comets having only been discerned during the past three centuries), the
calculated trajectories of some comets suggest they did indeed enter solar
space from elsewhere outside our system (and passed through without being
captured by the sun).
     On the other hand, there is a second reservoir of comets closer in: the
Kuiper Belt. Recent observations confirm the Belt exists and probably is the
source of the so-called "short-term" comets. Objects orbiting the sun within
this region are more likely to be perturbed by jovian-type planets. 

The current tentative conclusion,
>cozy solar systems free of billions of inner comments like ours are probably
>rare. 

     None of my colleagues, as far as I know, has reached such conclusions
regarding comets or the general nature of planetary systems within our
galaxy. We await more data. 

>A few more years research should settle the matter

     Ongoing research, we trust, will lead us to a better understanding of
the dynamics of solar system formation. It's doubtful we ever will be able
to settle the matter, only approximate reality within our limited (but
expanding) sphere of observations.

-= Tuck =-