Gas Giants

[dmvprof]

Have always been interesting to me. What keeps them from becoming solid?

(No, I'm not talking about flatulence )

[Nereid]

Ask a question, get a question! :P

What keeps the Earth's air from freezing (i.e. becoming solid)?

In more detail, what are the gas giants made of? At what temperature and pressure do those constituents freeze? Why are the gas giants - esp Jupiter and Saturn - very hot deep insides (say, below the first 2,000 km)?

[dmvprof]

So the answer is temperature?

[antoniseb]

Originally posted by dmvprof@May 11 2005, 08:15 PM
So the answer is temperature?

For the gas giants, it is the inability to radiate very quickly the gravitational potential energy of the collapse of the gas toward the center. This energy is trapped as heat, which slowly radiates out of the planet. If Jupiter survives the sun's transition to white-dwarfhood, it may be mostly solid in a few trillion years.

[Moseley]

I understood that the hydrogen at a certain depth was under such great pressure that it did solidify, although I am not capable of calculations to demonstrate this, so it may have been speculation.
While we are at it, I am intrigued to know about The Great Red Spot - does it go around with the rotation of Jupiter or at a rate related to the speed of the winds around the planet? Does the rate of rotation of the Spot itself vary? Obviously knowing what causes it would probably provide answers to these questions.

[wstevenbrown]

I understood that the hydrogen at a certain depth was under such great pressure that it did solidify, although I am not capable of calculations to demonstrate this, so it may have been speculation.

We're up againt the language. The H on top of the atmosphere are (mostly) the familiar diatomic H2 molecule. At the extreme pressure near J's core, it undergoes a phase change, and acts like a monoatomic alkali metal. The electrons drift (so do the protons), and don't belong to any particular nucleus (proton, usually). If this seems less than clear, it's because phase changes at extremely high pressure are not well-understood. It's cutting-edge science.

While we are at it, I am intrigued to know about The Great Red Spot - does it go around with the rotation of Jupiter or at a rate related to the speed of the winds around the planet? Does the rate of rotation of the Spot itself vary?

The GRS is confined to one of many atmospheric bands, each of which has its own characteristic rotation rate-- so if the GRS varies in rate, it is on a timescale of minutes, not even noticeable on such a large, diffuse object-- how would you measure it, with no 'solid' reference? The appearance of rotation in the spot is probably caused by shear forces inposed by the bands having differing rotation rates. There is still a lot of discussion about this, i.e., which motions are imposed from without, and which are intrinsic to the spot as an organized entity?

Good questions! S

[Relmuis]

The essential difference between a gas-giant and a terrestrial planet is that a gas-giant has no surface. Why not? Because at a surface gas must coexist with either liquid or solid of the same pressure and temperature.

When we descend into the atmosphere of a planet, we may at every depth measure both the pressure and the temperature. Connecting these data, we may then plot a graph of pressure against temperature. Into this diagram we may now insert a line which describes the pressures and temeratures where gas and liquid may coexist. This line ends at the so-called critical point. If our atmospheric plot crosses this line (passes to the left of the critical point) we will encounter a surface. Otherwise, we will not encounter a surface; therefore we are descending into a gas-giant.

Incidentally, Venus would be a gas-giant if she did not have a stony core inside her atmosphere. The carbon dioxide at ground level has a temperature and pressure beyond the critical point, and might therefore be called either a liquid or a gas.

[GOURDHEAD]

Incidentally, Venus would be a gas-giant if she did not have a stony core inside her atmosphere.

If there were a stony/metallic portion in the gas giants, where and in what state would it be?

[John L]

We can measure the motion of the Great Red Spot relative to the planet's rotation and the neighboring bands. Jupiter's rotation is the rate of rotation of its magnetic field.

[dmvprof]

So over billions of years of floating around and collecting stuff in space with it's gravitational field, presumably much of it solid, I wonder what happens to it all. Is it vaporized from the heat and transformed into more gas? Or if you were to somehow fly through the planet, would you get pelted from all of the pieces of solid debris floating around?

[alfchemist]

hello, dmvprof! Remember the shoemaker-levy comet that smashed into the southern portion of jupiter? I believe there's a wealth of data as to what happened to the comet (which exploded) as hundreds of observatories worldwide observed and recorded the event. This could provide tangible answer to your querry.

Maybe this site could help: http://seds.lpl.arizona.edu/sl9/sl9.html

[Moseley]

Thank you for the answers, Steven, and thanks John for the mention of magnetic field rotation. I hope the Jupiter orbiter mission proceeds without major obstacle as it seems there is so much to observe there.