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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

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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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Old 08-21-2011, 08:05 PM   #12
whswhs
 
Join Date: Jun 2005
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
That's the way I understand it. In effect he's sort of regarding the gas giants as a kind of "brown dwarfs." Of course when he wrote that they didn't really know about fusion and assumed that the heat of a celestial body came entirely from the conversion of potential to kinetic (thermal) energy during gravitational collapse.

Bill Stoddard
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Old 08-21-2011, 10:37 PM   #13
whswhs
 
Join Date: Jun 2005
Default Re: Planetary Romance and the outer planets

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Originally Posted by Fred Brackin View Post
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.
I don't think that that necessarily follows. The original nebula largely collapses into a central mass (the sun) and a bunch of smaller masses (the planets); the planets could in turn collapse into a central mass and a bunch of smaller masses (the satellites). The satellites would then cool and solidify much faster than the planets, just as the planets cool and solidify faster than the sun. So you could have the Jovian and Saturnian satellite be solid and compact while the planets were still fluid and diffuse.

I agree that that wouldn't work for a satellite as large relative to the planet as the moon is. And Phobos and Deimos and the minor Jovian and Saturnian moons could be captured sky junk. But Titan and the Galilean satellites don't seem impossible to account for as tertiary condensations.

It's all a rather elegant model and could be fun in a steampunk setting.

By the way, one of the Doctor Doolittle books has the good doctor and his kid sidekick Thomas Stubbins visiting the moon and learning that its near-immortal inhabitants vividly remember when it broke away from the Earth, leaving the Pacific basin behind. . . .

Bill Stoddard
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Old 08-22-2011, 12:38 AM   #14
Lord Carnifex
 
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Join Date: Oct 2005
Default Re: Planetary Romance and the outer planets

It won't correspond to any pseudo-scientific theory, but here's probably what I'd do:

Jupiter and Saturn have their own mini planetary systems, with the major moons home to a variety of settings.

Uranus is a bizarre and unsettling place. Its nearly 90 degree axial tilt causes the surface to become baked and frozen in violent seasonal shifts. All these temperature swings have caused the surface to buckle and crack, leading to rocky ground split by chasms and often interrupted by craggy and perilous mountain ranges. The natives look as though they were spawned in some opium nightmare, great winged things crossed between wasps and dragons, ridden by chitinous arachnids, seething with black ichor and hideous intelligence.

Neptune is a world of cold, windswept, stormy oceans and rocky island archipelagos offering some semblance of shelter. Adventures revolve around tall ships and those that prey upon them. In another word: pirates! With perhaps some steam-tech submarines, ala Twenty Thousand Leagues Under the Sea That is, when the natives - foul, squirming things, piscine or squidlike, with mad writhing tentacles - aren't emerging from the depths to attack ships or settlements in the manner of "The Doom that Came to Sarnath" or "The Shadow over Innsmouth".

Pluto is strange and eerie, shrouded in darkness and eternal frosts. It's clear that the world was once inhabited, gloomy temples and blasphemous monuments attest to that. But now, nothing moves but the shadows. Wait. What was that? Did you see someth-
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