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Re: On making Earth-like planets

I would tend to disagree with Taylor who has been embarassingly thick headed
on some key planetary issues in the recent past--like his passion for Harold
Urey's "cold Moon" theory as well as a humorous paranoia when it comes to
discussing tektite origin theories other than his own pet ideas. Also, a
horse-blindered attachment to chemistry as the only "means" to unlocking a
planetary mystery is another of Taylor's hallmarks. On topic: Earth-like
planets may be more likely to be found as orbiting moons around Jovian
worlds.  I think Taylor is one of those dour scientists who see life as
something random and unique.  Yes, Sagan would strongly disagree with Taylor
as would many other scientists on many of Taylor's ideas.

<<< Jim Hurley <hurleyj@arachnaut.org>  6/ 2  6:04p >>>
I have just finished reading a fascinating article
in the Meteoritic and Planetary Sciences Journal that
just arrived.

It is by Stuart Ross Taylor who wrote The Evolution of the Solar System -
a New Perspective.

Taylor was involved with the Lunar recovery mission at NASA and has a broad
background in geology, astrophysics, and chemistry. A rare mixture
of talents needed to synthesize the results from our exploration 
of the solar system these last few decades.

He argues that the origin of planetary systems is largely chaotic.
We have observed a small number of other planetary systems recently via
Hubble -
each is unique.

All planetary systems must have evolved from molecular clouds
emitted from supernovae events, because the early universe had
only hydrogen and helium - all other matter resulted from nucleosynthesis
in mature stars.

When the molecular clouds settle into star systems, the initial angular
momentum and distribution of matter dictates whether there will result
a single star or multiple star system - most stars form multiple star
systems.

Probable only single star systems can evolve planets with potential for
life.

Even in the infrequent single star systems that evolved from the first
generation
stars, most will evolve a Jupiter-like object at the ice point in that solar
system.

This early planet will dominate the evolution of the rest of the planetary
system.

If the star that is forming in that cloud has ignited coincident with the
formation of
the Jupiter object, it will sweep out dust and gas in the inner planets
formation area;
if not, the Jupiter object will be exposed to the dust and slow down -
winding into an
orbit close to the new star and obliterate any possible earth-like planet.

Taylor goes on to discuss that the habitable range in a star system is very
narrow,
and the likelihood of a planet format at that region only a matter of
chance.

Many more details are presented; his conclusion being that even with 500
billion galaxies
of 100 billions of stars each - the chance are still minute that another
earth-like
planet will have been made.

Even those that do happen, they still endure the planetary bombardments that
must be common
on solar systems - events that obliterate planetary atmospheres or severely
impact the development
of life every few millions years - giving advanced life a very narrow window
of time to evolve
before a major disaster occurs.

When the requirements that plate tectonics to provide heavy minerals for
technology are added,
along with a large satellite to provide tides for life to evolve, it seems
to me his arguments
are very persuasive.

Carl Sagan would undoubtedly object to much of this if he were alive, but I
find Taylor's argument
to be very moderate, level-headed, and sobering.


--
Jim Hurley  Freelance graphics artist
Web page design; graphics; multimedia
  <URL: http://www.arachnaut.org/ >

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