Atmosphere - Page 4

Krakenup · #31 January 31st, 2001, 09:15 PM

quote:
Originally posted by apache:
Um, where did you get that 'surface gravity' information? I hope you realize that gravity is a function of mass, not density. There also is absolutely no scientific information about the 'surfaces' of any gas giants, just theories.

Well, uh, you could use a search engine such as Yahoo and search on "planet surface gravity" or something similar and look at one of the thousands of references. Oh, and it absolutely is a function of density. Read one of the references.

jimbob55 · #32 January 31st, 2001, 09:41 PM

If you're talking realism...
How do hydrogen /methane/ CO2 breathers invent fire? + how do ice planet dwellers invent fire?
How do gas giant dwellers (The colony base pic looks like it is hovering somewhere in the upper atmosphere) invent anything?
You can't mine iron without VERY LONG drill bits and of you can't make very long drill bits without carbon steel.

Alpha Kodiak · #33 January 31st, 2001, 09:45 PM

As far as the strength of a gas giant race is concerned, the real question is, what type of life would evolve on a gas giant? If you look at the race portrait of the Eee, they look more like bubbles than anything else. Probably not very strong in hand-to-hand combat. (As my son put it, all you would have to do is pop them.)

I have always pictured a gas giant race as one that floats/flies in the upper atmosphere of the gas giant. That also meshes with the baloon-like appearance of the gas giant colonization tech.

Whatever life there would be on a gas giant, I think we can safely say that it would in no way even remotely resemble life on a rock world.

Cybes · #34 January 31st, 2001, 10:29 PM

to the many people with issues regarding the diamond-core theory:
i didn't think it up. nor am i an astrophycist or a chemist - just someone who reads a lot. i can't answer all of your questions. if you want to take this up seriously, ask in sci.astro, or of an applicable scientist you know, or even consult a library. books are, after all, where i heard about the idea in the first place.

puke: as rdouglas said, though, solid is the densest form of most elements. given the pressure at the core of a jovian planet, i'd reckon any carbon present would pretty much have to be in the densest form available. so, it's a hot diamond.

rdouglas: i think you answered your own question, didn't you? iron is 'heavier' than carbon, so that's what's at the centre. whereas, carbon is 'heavier' than the majority of elements on a jovian, so that is at the centre instead there.

(sorry it took so long to reply - timezones are a *****

)

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"Just think of it as Evolution in action" - 'Oath of Fealty', by Larry Niven & Jerry Pournelle.

PeteB · #35 January 31st, 2001, 10:58 PM

Re: Planetary Cores:Off-topic Alert!

I'm not an expert either but...

Planetary cores are not generally "static" objects, especially in cases like Gas Giant planets. That there is a solid core at all is questionable (hence "surface gravity " is a debatable term - surface of what?) Here's the thing, Earth has a liquid core, not a solid one. There is no question of Carbon congealing at the center and forming diamonds - the whole mass is in motion. Similarly, most current theories about the nature of gas giant planets are such that the gases and other elements and compounds are constantly moving, fissioning (splitting) and fusioning (combining) under intense conditions of heat and pressure. Much of the lower atmosphere of the GG is probably in a "plasma" state (fourth - or fifth, depending on how you count - state of matter, neither solid, liquid or gas). In this state electrons are generally stripped from thier atomic cores - very energetic, polarized and turbulent. No diamonds here.

For an example of a Gas Giant creature, see Roger Zelazny's story in the collection "Frost and Fire" (story name escapes me) which is basically a jellyfish with tough sides.

Puke · #36 January 31st, 2001, 11:28 PM

since we have completely destroyed this unsuspecting little thread, i will ask:

does anyone remeber what the gas giant hydrogen breathers were like in the David Brin books (uplift/startide/sundiver)? i dont, but i remember he had 'em.

Cybes · #37 January 31st, 2001, 11:48 PM

i only mentioned it is an aside. a mild attempt at humour, really. never expected it to spark such controversy.

as i said, it's not my theory, and i'm not the one to take it up with. it's also an older theory ("cosmos" was early 80s, i think), and may have since been discarded while i wasn't watching.

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"Just think of it as Evolution in action" - 'Oath of Fealty', by Larry Niven & Jerry Pournelle.

apache · #38 February 1st, 2001, 01:44 AM

Well, I looked up planet surface gravity, and all kinds of other stuff just to find out where you got your information. Yes, I did find plainly given stats that claimed the surface gravity compared to earth's surface gravity. Now, I calculated through the numbers using the universal law of gravitation, and the maximum radius of Jupiter. This gives the aforementioned statistics that Jupiter's surface gravity is approximately 2.5 times that of earth's. However, the fact is that the 'surface gravity' here is the gravity at Jupiter's outer atmosphere. We don't know where the surface of Jupiter actually lies, and as such, using such a statistic to calculate gravity at the 'surface' of jupiter is pretty ridiculous. If Jupiter had a solid core the size of earth, for example, the gravitational acceleration there would be about 3520 times that of Earth's.
Oh, and I still have no idea where you found that gravity is some function of density, because its absolutely untrue. It is a function of mass and distance only. This is related by the equation, a=GM/(r^2) where M is the mass of the planet in kilograms, r is the distance from the center of that planet in meters, and G is the univerersal gravitational constant, 6.672*10^-11. This gives you the acceleration due to gravity.

Puke · #39 February 1st, 2001, 01:53 AM

quote:
Originally posted by apache:
Oh, and I still have no idea where you found that gravity is some function of density, because its absolutely untrue. It is a function of mass and distance only. This is related by the equation, a=GM/(r^2) where M is the mass of the planet in kilograms, r is the distance from the center of that planet in meters, and G is the univerersal gravitational constant, 6.672*10^-11. This gives you the acceleration due to gravity.

im with you on all your statements, and it really supports what i was thinking. i have to point out though, that you could derive density from mass and distance (although you could obviously not do it the other way around).

Krakenup · #40 February 1st, 2001, 07:32 AM

quote:
Originally posted by apache:
Well, I looked up planet surface gravity, and all kinds of other stuff just to find out where you got your information. Yes, I did find plainly given stats that claimed the surface gravity compared to earth's surface gravity. Now, I calculated through the numbers using the universal law of gravitation, and the maximum radius of Jupiter. This gives the aforementioned statistics that Jupiter's surface gravity is approximately 2.5 times that of earth's. However, the fact is that the 'surface gravity' here is the gravity at Jupiter's outer atmosphere. We don't know where the surface of Jupiter actually lies, and as such, using such a statistic to calculate gravity at the 'surface' of jupiter is pretty ridiculous.

Well, if you want to be picky

, but remember that when you get all the way down to the center of Jupiter, gravity is zero because you have an equal amount of mass pulling in every direction. The pressure is pretty high though. The point, however, is that raynor and Barnacle Bill posted about how high gravity would be on a gas giant, but it isn't. It's similar to Earth's in many cases because of the low density of gas giants.

quote:
If Jupiter had a solid core the size of earth, for example, the gravitational acceleration there would be about 3520 times that of Earth's.

I'll have to question your math here. Jupiter has 318 times the mass of Earth so if it were the same size as Earth, it would have 318 times the density and, consequently, 318 times the gravity.

quote:
Oh, and I still have no idea where you found that gravity is some function of density, because its absolutely untrue. It is a function of mass and distance only. This is related by the equation, a=GM/(r^2) where M is the mass of the planet in kilograms, r is the distance from the center of that planet in meters, and G is the univerersal gravitational constant, 6.672*10^-11. This gives you the acceleration due to gravity.

Perhaps you weren't aware that mass is a function of density, namely density times volume, and that the volume of a sphere is a function of r^3 (4/3 pi r^3 IIRC). Therefore, the simplest form of the gravitational equation is a constant (4/3 pi G) times density times radius. So if you used this form of the equation, gravity would depend only on density and radius. In reality, the three variables (mass, density and radius) are interrelated, and the equation can be written using any two of the three. You can, however, have two planets with identical masses but different densities that have widely different surface gravity. In that case, gravity would vary with density to the 2/3 power.