[ExI] Dawn's Early Light: Ceres and Vesta

Jeff Davis jrd1415 at gmail.com
Mon Jul 9 00:54:41 UTC 2007


On 7/8/07, Amara Graps <amara at amara.com> wrote:
<snip>
> ...here is my own rocky road list of science
> questions that I would like the Dawn mission to help answer.
>
>      * Where is the snow line and hence the emergence of water in the
>      formation of the inner solar system?
< snip>

This is one of my questions as well.  Well, sort of.  I'm interested
in primordial methane and
other hydrocarbon species.  I want to know how much of these were
accreted during the earth's formation.

Some years ago I discovered the dispute over the origins of the
earth's "paleo"hydrocarbon inventory -- you know, oil, gas, coal, tar
sands, oil shale, etc. Soviet theory, adopted (if not plagiarized) by
Cornel's Thomas Gold, theorized a primordial origin, while the
conventional (western) view posited a paleobiological origin, ie the
"fossil" fuel idea.  I came to favor the primordial origin, and tried
to find out just how much primordial hydrocarbon had been accreted
into the primordial earth.

This led me to look into the process by which the solar system formed
from the ejecta of novae and supenovae.  As I understand it, local
ejecta density from multiple sources increases to a point where
gravitational forces come to dominate.  The "cloud" begins to
"infall"(ie contract), spin, and heat up.  The interaction of the
forces and particles forms the material into a disc.  As the
infalling, spinning, and heating continue, the constituent material is
"processed", simultaneously thermally fractionating and physically
clumping together, forming a spatial distribution of "particles" of
diverse sizes and compositions. This was an ongoing process featuring
an ever increasing particle size, starting with molecules and "dust",
and ending with a star, planetary bodies, and a remnant of the
starting materials.  When the bulk of the starting material had been
"swept up", the infalling and heating effectively ended, leaving us
with the solar system as we know it.

What I learned regarding the formation of the solar system gave
sharper focus to my question about primordial hydrocarbon inclusion in
the forming earth.  I then had a notion of the factors upon which the
answer would depend.  Which seemed to be:

(1) Quantity and variety of hydrocarbon species in of the starting
materials, and their thermal characteristics (freezing and boiling
points, and, to a lesser extent, their decomposition temperature);

(2) The time dependent radial thermal gradient in the protoplanetary disc;

(3) The time dependent spatial distribution of hydrocarbon species
(varies over time as a result of thermally driven fractionation) in
the protoplanetary disc.

 (4) The time dependency and "clumping" behavior of the range of
smaller bodies which eventually fuse to form the planetary bodies.

You see, the gravitational infalling heats up the protoplanetary disc,
creating a radial thermal gradient -- hottest at r=0, and decreasing
outward.  Volatile species sublimate and "boil off" outward in the
disc.  (Thus the rocky inner planets and the outer gas giants.)  This
takes time.

Meanwhile, non-volatiles and ices(solidified volatiles) are clumping
to form ever larger bodies, which, it would seem to me, would entrap
volatiles, protecting/preventing them from boil-off.  The larger the
body, the greater the protection.

So, regarding the inclusion of hydrocarbons in the primordial earth,
it would seem there were these two processes working against each
other: disc heating which drives volatiles radially outward in the
disc, and particle "clumping" which tends to trap volatiles in the
interiors of ever-larger"particles"/bodies despite ambient disc
temperatures otherwise sufficient to boil off unprotected volatiles.

And that's where I left it.

Sorry about no links.  It's been a few years since I explored this matter.

Not sure why I chose to write this.  Hope it's not too tedious.  Maybe
someone out there can help with filling in the blanks.

Life is grand.
-- 
Best, Jeff Davis

               "Everything's hard till you
                     know how to do it."
                              Ray Charles



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