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

[Jeff Davis]

Thank you for your response, Amara.

On 7/9/07, Amara Graps <amara at amara.com> wrote:

> Dear Jeff,
>
> In your description, I didn't see the emphasis on the condensation
> sequence that should be there,

I was desperately trying to be brief with a subject which gets more
complex by the day.  When I was a kid, we had the sun, the planets,
the asteroid belt and the occasional comet.  It was simple and it was
static.

I started by referring to your interest in "the snow line" (water ice)
as similar to my interest in the methane (in particular, hydrocarbon
species in general) "snow" line.  Aren't these two points along the
condensation sequence?  And there are a bunch of hydrocarbon species
all with different pressure/temp condensation values, no?  More points
in the sequence, no?  Then nitrogen, oxygen, CN, CO, HC, and of
course, hydrogen, all with condensation values corresponding to lower
temps and greater heliocentric distances (than methane), no?  I didn't
mention N, O, CN, etc, because I was focusing on methane/hydrocarbons.

However, communication is hit and miss, and inferences aren't always
apparent.  But no matter.  One has to start somewhere, and that's what
I did, and I must say, with great success.  You jumped right in, gave
me something to work with, and energized me to revisit the subject.
And I've been having a great time doing just that.  Much thanks.  I
can only hope you're having as much fun as I am.  (It's a welcome
respite from the gloomy and frustrating political crap that I've been
obsessing over for the last six years.)

> and I think your time sequence is not
> really in order. The molecules didn't form during the planet forming
> part, but much before,

By gas and plasma phase chemistry in the interstellar medium.  I was
hip to that.  Like hydrogen ions impinging on graphite grains. (Which
I only just learned yesterday in my reading provoked by this thread.)
There are so many delightful details.  On my walk in the woods today
with the dogs, I began wondering about the interaction cross section
for a hydrogen atom (or ion) in the interstellar medium.  I read that
there is on average one H atom per cc and 1/100 th that much non-H, so
I thought, "How far must a H atom travel, statistically speaking,
before striking a non-H atom?"

It's easy to accept the "primordial soup" of the early earth as a vast
and diverse chemical experiment, but the vast expanse and
"emptiness"(not!) of interstellar space?  Who woulda thunk it?

I'm one happy camper, with an abundant serotonin flow.

Loved you use of "solar blob",

> After the molecular cloud collapses (triggered by a supernova or few, or
> some other kind of 'shock') to form the "solar blob"...

A technical term, no doubt.  ;-) .

> and were incorporated into the solids that became
> the planetesimals, that became the embryos, that became the planets.
>
> After the molecular cloud collapses (triggered by a supernova or few, or
> some other kind of 'shock') to form the "solar blob", which becomes then
> a "protostar+ gas/dust disk (because angular moment is transferred out,
> while  material transferred in), which becomes a star+gas/dust disk
> (fusion has turned on in the protostar), then we have a solar nebula,
> where solids form dependent on the temperature and pressure profile of
> the nebula, which is time-dependent, as the nebula disk cools too. So
> one sees a molecule formation pattern as a function of heliocentric
> distance and time. It's very model dependent, as you can imagine. I say
> that I would like to know where was snow line during our solar system
> formation, which you interpreted as a large unknown.

Please forgive me.  It certainly is unknown TO ME, because, well, I'm
just an amateur.  A dilletante, if you will.  If I had access to the
models, and the skill and diligence to study them, it might not be
quite so unknown to me.

But speaking of clear communication.... When you speak of the snow
line, I get the impression of a static location. I infer from the way
you speak of it that it's *effectively* static during the
planet-forming period. But the process of contraction and compression
heating of the gas cloud, and then (the discontinuity of) solar
ignition and the new heating and cooling regime brought on by that...
well, the condensation sequence would I think, (before reading the
materials on the condensation profile which you have provided) be
changing quite a bit re heliocentric distance over that time scale.

Anyway, I have quite a homework assignment to catch up with,
condensation sequence and that new stuff you posted a link for today,
so I'll leave it at that.

<Snip the rest>

-- 
Best, Jeff Davis

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

PS You've got a little somethin' waitin' for ya back in the states.