From: Robert J. Bradbury (bradbury@aeiveos.com)
Date: Wed Jan 08 2003 - 15:52:28 MST
On Wed, 8 Jan 2003, Eugen Leitl wrote:
> So there's no wonder that molecular clouds have a very different element
> abudancy than interstellar medium, and large structures formed by
> gravitational accretion have other abundancies still. Especially, after
> the separation (siderophiles/siderophobes).
Granted. The composition of molecular clouds and the interstellar medium
will be different -- the question is *how much different?*. The "bubble"
we inhabit is seems likely to be depleted of almost everything. This would
seem to be a characteristic of real "bubbles" where high energy UV radiation
and supernova explosions have pushed much of the material away from former
high density cloud (star-forming) regions. So the element make-up of
solar systems become really a question of whether you formed a low-mass
(e.g. solar mass) star early in the history of a star-forming high density
cloud (i.e. you by and large get interstellar abundances) or late in the
history of a star-forming high density cloud (in which case you get the
interstellar abundances "contaminated" by the recent SN ejecta from high-mass
short lived stars (e.g. those exploding after only ~100 M years). I think
that there is a some evidence that the 2nd case may be more valid for our
solar system.
However, I don't believe these scenarios impact Li quantities significantly.
Most of the Li in the universe was created during the big bang. I believe
that brown dwarfs and stars primarily consume it rather than create it.
So its on a downhill abundance path until we start breeding it in (very)
large quantities. The ratios of Li in the Earth's crust and oceans show
that concentration effects can significantly transcend the initial conditions.
My primary point was to show that Kuiper belt objects, lacking many of the
"concentration" effects, may have more "natural" abundances and those abundances
may not be "ideal" for constructing technologies that are required for plutino
colonization. As a result one may need inner solar system mining and/or
inner-to-outer solar system material transport capabilities to be able
to effectively colonize the outer solar system. Either that or one has
to come up with a fusion cycle that can utilize relatively abundant fuel
(H/D only?) and doesn't require Li for an extraction of the energy generated
if one has any hope of utilizing the resources of the Kuiper belt anytime soon.
Robert
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