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Re: Stimulating questions


The topic of the formation of the solar system, and the asteroid belt,
is indeed stimulating and controversial.

While I am no expert on the subject, I am keenly interested in this
and I've been reading up on recent research. In particular, a book
called 'Chondrules and the Protoplanetary Disk' made up of
papers at a recent scientific convention (I believe it was the
Lunar & Planetary Society 1995, but the book is at home).

Most scientist agree that the pre-solar system was formed from a
disk of dust that was seeded by solar wind particles from a nearby
supernova. This injected hot particles and turbulence, etc. into the
cloud.

Eventually the cloud formed a condensing disk and the central mass
entered a pre-stellar phase called T-Tauri. Shortly thereafter
the mass reached the critical temperatures and pressures needed to
fuse Hydrogen to Helium and the Sun as we know it was born.

The solar wind blew away most of the tiniest dust specks and the
planets formed from accretion of the remaining debris.

Some say chondrules formed in this T-Tauri phase and therefore are
pre-planetary forms, others say the developed after the sun formed
and matbe during thhe time the planets were forming.

In the T-Tauri phase of a star the size of our sun there is a
well-defined temperature gradient over the pre-solar disk.
The temperatures in local areas favored the condensation of
certain materials - with the area from about 2 to 5 AU being
the area where most materials condense - at 2 AU the temperatures
favored only the refractory material and at 5 AU liquids and ices
could condense. Everything was gaseous from the core up to about
2 AU.

That is why the solar system has heavy dense planets nearer the sun
and low density gaseous planets farther out - they were formed mostly
from the nearby material at hand.

Jupiter or a planetary object like it may have formed early and at a
large size because of the preponderance of gaseous compounds that
condensed from the dust cloud and supernovae material.

I think most scientists would argue that there were hundreds to
thousands or more protoplanetary bodies - the number arbitrary based
on what size you want to pick to call something a protoplanet versus
a big rock.

During the phase of planetary accretion, the collisions of this hot
material usually caused fragments to merge - probably many collisions
were rather gentle and two objects just melted together, but later
as things cooled off the collisions were more violent and the
objects could smash up and make more rubble.

The early formation of Jupiter prevented almost anything large from
forming in the 2.5-4 AU area due to orbital resonances that still
fire asteroids our way.

I sometimes wonder if it is inevitable that a large object would form
at the 100K to 300K temperature area from a disk made up of dust and
supernovae debris. That's about where Jupiter would be if it were
largely formed during the T-Tauri phase. I imagine a dust cloud
with a rim of ices and carbonates forming there and the mush is
forming like a snowball rolling down a snowy hill.

I welcome any corrections to this note - I'm still trying to
assimilate all the stuff I've been reading lately, and I don't
get any other feedback besides what happens here on this list.

-- 
          Jim Hurley
       Arachnaut's Lair
http://www.arachnaut.org/ >
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