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Old 08-21-2011, 07:06 PM   #11
Fred Brackin
 
Join Date: Aug 2007
Default Re: Planetary Romance and the outer planets

Quote:
Originally Posted by isf View Post

Do I have this nebular theory correct?
1 Nebula starts contracting and cooling off leaving rings.
2 The rings cool off and form planets
3. the planets go from suns to gas giants to rocky bodies through cooling and contracting (the differences being size and age)
4. planets may cool and contract enough to explode like the fifth planet
The quote Bill found introduces size and Laplacian contraction into the mix. This means large planets cool slowly while small ones cool quickly.

So for any planet somewhere between your stage 2 and 3 there is an incandescent gas phase (like the Sun) to a dark gas body phase (Gas giant) to a warmish (internal heat) solid matter phase. This would proceed to a cold rock phase with an airless/watrterless condition.

Mercury would have cooled the quickest but started the latest. Jupiter would ahve started before Mars but Mars would have cooled far faster so unde trthis theory Mars is much "older" in geological terms than Jupiter. Mars is also much older geologically than Earth and might easily be moving out of an internal heat phase to cold rock.

The exitence of the Moon is a problem for nebular cooling theroy. Double planets would not hapen naturally and indeed modern theories of the Moon's formation are decidely catastrophic.

I do not believe your stage 4 is inherent in the process. It would stop at the cold solid stage. Even as late as the early 60s SF writers were having the lost fifth plaent be destroyed by various cosmic catastrophes such as the actions of Valentine Michael Smith's elder Martians.

It is only sometime in the mid-60s that everyone gave up and had the initial formation of any planet between Mars and Jupiter be aborted by Jupiter's gravity.

The Galilean moons of Jupiter have much the same problem as Earth's Moon. They obviously came from somewhere else and being small should be geologically old, all other things being equal. All planetary moons would probably have to be captured in this theory.

That measn the earlier you are and the fewer moons you have to explain, the better.

A key actor is elapsed time. The 1700s mathematician Rene LaPlace deduced that the source of the Sun's energy could be explained by the Sun shriking 1 mile per year. This would mean that he Sun had only 400,000 years left. Beign a million times smaller than the Sun the Earth would have contracted and cooled in only a handful of years.

So an important thing to remember si not to look too closely or apply to many modern numbers to this theory. It will not hold up well.
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