Questions about gasgigants

[ArneB]

I have a few questions regarding gas gigants to anyone who knows a little about the subject:

- What factors affect the colour of a gas gigant? Is it the type of gas, the wind speed, the temperature, or other things?

- Is the windspeed and turbulence very dependent on the energy received from the sun?, If so, how come Neptune appear to be more "turbulent" than Uranus? Is it tidal forces?

- What makes cloudbands form? They appear to have something to do with the rotation of the planet. How come the gas separates into distinct band, usually of different colors? And how come the rotation speed of the bands seem to be quite different? Some even appear to rotate in the opposite direction.

- Why is jupiters red spot so stable, and why is it red?

-Do extrasolar planets close so ther star slowly boil away? Is it thus likely that they have something that looks like a comet tail?

It would be great if someone could enlighten me on this. I am thinking of the possibility of making a Navier-Stokes solver that could "semi-simulate"
the appearance gas gigants.

[Cham]

The color is very dependant of the parameters you listed :

-chemical composition (atomic and molecular types, viscosity)
-temperature (proximity to the star)
-atmosphere pressure and density (so the mass of the planet is important),
-star color (spectral type), because the star is the light source.

The band aspect and turbulence depends on the planet rotation on its axis and also on the proximity to the star (temperature). Temperature may causes convection and heath transfer.

So all in all, it' VERY complicated. I guess you can put any color and almost any turbulence to any gaz giant around any star.

The red spot on Jupiter isn't really red, by the way. Apparently, it's supposed to be all white !! It appears red on some pictures because of the poor amount of light received and some exagerated contrasts. It's like taking a picture with a normal camera in a place without enough light. You get very often a dark picture with some red everywhere. But I'm not sure of that explanation. Maybe someone could comment on this.

The big "red" spot is permanent, because it's a caracteristic of some fluids rotating on a sphere. I think that it's topological in nature. It was reproduced in some laboratories recently (well, some years ago, actually). There's was also a great spot on Neptune (or Uranus ?). It's not as visible as on Jupiter, however. Apparently, it disappeared recently and I don't know why. Maybe it's just because it's not "visible" anymore, but it may be there anyway.

[maxim]

I remember a laboratory experiment for the banding and stability questions:

A glass cylinder (size of about a small refrigerator) contained another rotating cylinder of which the rotation speed could be adjusted. The gap between outer and inner cylinder (of about a few milimeters) was filled with fluid, containing (very small) metallic particles. While raising the rotation speed, there where phases of turbulence, followed by phases of stable banded formation, followed by turbulence, and so on.

At certain speeds the stable banding and (like the red spot) local rotation spots suddenly turned into wild turbulences with no recognizable patterns. The further raise of the speed then slowly established new stability structures inside the fluid.

So I think if a gasgiant has banded or unbanded patters, or no patterns at all, simply depends on a balance between rotation of the planet, atmosphere thinkness and atmospheric friction. Perhaps one can find theories out there that tell of how much the jupiter rotation speed has to be slowed down to make him lose his banded patterns.

maxim

[ElPelado]

Does anybody have a link to something about that experiment?
About the red spot: its a storm, and its not permannent. I think I ve read that it can dissapear anytime, as Neptune's dark spot(also a storm) did...

[ArneB]

Thanks for the info!

Maxims experiment was particulary interesting, regarding the fact that there seemed to be different stability structures for different speeds. That explains why there are several different bands at different lattitudes (I'm not sure which is which ) The rotation speed i simply different. There are also differences in the amount of light recieved. But what causes the friction? There is certainly no friction against space. Could it be that heated gas from the lower layers rise, and is slowed down because of the Coriolis effect? Did you note the Reynolds numbers in the experiment to see if you could find any relation to the real world of gas gigants? Or is it simply too complicated to ever be figured out?
Again, thank you for the answers.

[eburacum45]

The color is very dependant of the parameters you listed :

-chemical composition (atomic and molecular types, viscosity)
-temperature (proximity to the star)
-atmosphere pressure and density (so the mass of the planet is important),
-star color (spectral type), because the star is the light source.

The band aspect and turbulence depends on the planet rotation on its axis and also on the proximity to the star (temperature). Temperature may causes convection and heath transfer.

So all in all, it' VERY complicated. I guess you can put any color and almost any turbulence to any gas giant around any star.

I'd go with that;
the red colours on Jupiter and yellowish colours on Saturn are probably due to small impurities like organic compounds or perhaps phosphorous and or sulphur; the blues and greens of Uranus and Neptune are generally explained by methane in the atmosphere, which is greenish; other compounds will add other colours...
you could even have colouration from chlorophyll or other light absorbing pigments, if such a thing as atmospheric plankton has developed.
larger worlds and small brown dwarfs might glow dully red...
you have an entire pallette here, so almost anything might be possible.

A little fun with Imageforge and the gas giant textures the basic Celestia package, from the Solar System generator and elsewhere can make some pretty worlds-
http://www.eburacum45.5u.com/Gas_Giants.html
(most of these are test worlds, so please ignore the radius; I made these images while I was looking for mismatches in the texture edge- you can see one such mismatch in the image of Da costa)...

(and no, most of these textures are not available yet from the Motherlode- but they soon will be...)

[maxim]

Arne,
I didn't to the experiment myself, just watched it on a video report some years ago. You may look on the net for 'fluid dynamics' and 'flow patterns' to find some good information. Those kind of experiments are used regularily in oceanographic and atmospheric studies.

maxim

[Evil Dr Ganymede]

I have often wondered about gas giant colours...

Is it coincidence that Jupiter and Saturn are Hydrogen Giants and are yellow/red/brown colouring, but Uranus and Neptune are Icy Giants and have green/blue/white colouring?

Would all the colour palette be available for gas giants, or are there some colours that you wouldn't be likely to find? (eg lurid pink, neon blue, etc )

[ArneB]

Ok, guys, before I lay this thread behind, I just want to share one thing.
I am currently studying mechanics, (both fluid and solid) and I'm quite facinated by flow patterns and numerics. If you want an example of a realtime Navier-Stokes solver, you should check this link out:

http://www.nullsoft.com/free/smoke/

It's merely a toy - a plug-in for Winamp, but it actually utilizes the GPU to solve some quite advanced equations, and the result is really facinating. If you download it, or just browse the screenshots section, I'm sure you'll find the striking similarity with the patterns produced, and the patterns of gasgigant cloudbands. I am sure a little tweaking with the source code could produce a neat procedural texture for gasgigants in Celestia. The BBC-documentary "The Planets" has actually gone all the way, and if you watch the film, you'll see that they have made a procedural texture for Jupiter - most likely also with the help of NS-equations.

Also, did you know that NS-equations are used in the weather forecast?
So this is actually the mechanism that governs the weather. Perhaps, with a LOT of work, it could be used to create a realistic cloud texture. I strongly doubt anyone has the interest or time to try (I'm not a programmer myself) but heck, it's allowed to dream.

[ArneB]

Maxim, I think I might have found the experiment you were referring to, along with cfd simulations of jupiters red spot:

http://www.me.berkeley.edu/cfd/videos.htm

[maxim]

Yes, these simulations are quite similar to what I saw - only that 'my' experiment was real physical.

maxim