Why can’t gas support a solid body?

[starstruck_]

I was working at the observatory and uh someone came in with a question about landing in Jupiter- right away my brain was like no, it’s a gas giant and there’s too much pressure for a probe to make it to the solid surface, but I’ve also been trying to think of it in terms of the force applied by the gas on a solid object.

When you have a gas, it definitely cannot provide the required upwards force needed to go against the weight acting on a solid object. What if you had a high enough mass of gas, and high enough pressure? Would it still not work because 1) the particles aren’t always hitting the solid object (I thinking of a small solid object in this case) and 2) when the pressure is high enough to support the object, the pressure outside is greater than the inside and so the object crumbles and won’t be “landing” anyways 3) gasses are always in motion so the same amount of gas isn’t always under the object This wasn’t a very complicated question, but I’m just wondering what happens at a smaller scale, because why not.

 

[anorlunda]

Is it any different than an object floating on water? It should strictly a matter of buoyancy and the density of the object and the gas. Besides, if you're above the triple point, there is no difference between gas and liquid.

 

[starstruck_]

Is it any different than an object floating on water? It should strictly a matter of buoyancy and the density of the object and the gas. Besides, if you're above the triple point, there is no difference between gas and liquid.

I don’t think it’s much different, the floating on water is what I initially thought of which made me think of this.

Thank you! [emoji5]

 

[Borek]

It can't?

 

[starstruck_]

It can't?

View attachment 220473

Ouuuu I didn’t even think of that!

I was thinking more of in terms of “landing” and a solid object like a metal box etc

 

[Janus]

For an an object to be buoyant in a gas, it's density must be less than that of the gas. The lightest metal is lithium and the heaviest known gas is Tungston Hexafluoride. At anything over 41 atm of pressure, The Tungston Hexaflouride would be denser than the lithium and thus a hunk of "lithium" would float in it. (not for very long, lithium is a very reactive metal and Tungston Hexaflouride is a corrosive gas).

One problem you can run across is that as you increase the pressure of a gas to increase its density, you can compress it to the point of it leaving the gas phase and becoming a liquid. In the above example, Tungston Hexaflouride is still a gas at that pressure and at room temperature.

Nitrogen, the main component of our atmosphere, on the other hand would become a liquid at pressures much lower than needed for it to reach the density for it to "float" lithium.

 

[A.T.]

When you have a gas, it definitely cannot provide the required upwards force needed to go against the weight acting on a solid

 

[Dale]

When you have a gas, it definitely cannot provide the required upwards force needed to go against the weight acting on a solid object.

Hmm, you seem to be forgetting airplanes, birds, helicopters, insects, hovercraft, balloons, dust, etc

 

[CWatters]

You can float a tin foil boat on sulphur hexafluoride. Videos on YouTube.

 

[sophiecentaur]

I don't think we are being quite fair on the OP. The obvious answers are 1. that gases are low density and only a very few solid objects can displace their own weight of most gases and 2. that gases have very little structural strength. The force that a gas can exert can be due to viscosity or the Bernouli effect. But both of those forces require the gas and the object to be moving relative to each other.

 

[ZapperZ]

With a high-enough pressure, a gas can certainly "support" and even push against a solid. After all, that is how a pneumatic pump works!

This question should have been broken down into separate parts. First there is the principle of whether it is possible for gasses to exert such a force. Then it is the question on how feasible it is to do that for the scenario that the OP has stated. Those two are separate questions, the 2nd being only a logical follow-up if the first has a positive answer.

Zz.

 

[Martin0001]

I was working at the observatory and uh someone came in with a question about landing in Jupiter- right away my brain was like no, it’s a gas giant and there’s too much pressure for a probe to make it to the solid surface, but I’ve also been trying to think of it in terms of the force applied by the gas on a solid object.

When you have a gas, it definitely cannot provide the required upwards force needed to go against the weight acting on a solid object. What if you had a high enough mass of gas, and high enough pressure? Would it still not work because 1) the particles aren’t always hitting the solid object (I thinking of a small solid object in this case) and 2) when the pressure is high enough to support the object, the pressure outside is greater than the inside and so the object crumbles and won’t be “landing” anyways 3) gasses are always in motion so the same amount of gas isn’t always under the objectThis wasn’t a very complicated question, but I’m just wondering what happens at a smaller scale, because why not.

Pressure of gases (hydrogen, helium, methane, ammonia) on Jupiter is extremely high. Under such a pressure gas will have huge density.
At such density normal rocks would be floating in this gas.
So rocky surface of Jupiter if made of common materials known on Earth would simply dissipate in gas and float.
So we suspect that Jupiter don't have Earth like core - this would simply disintergare and float up.
There maybe a core there made of metallic hydrogen, which is a form of *degenerate matter* and possibly of very high density, much higher than materials on Earth but we don't really know.
Noone was there and the only probe sent was able to penetrate only tiny proportion of upper atmosphere.
Even here on Earth we can experimentally get conditions where air *sinks* in water.
This would happen at approximately 8000 bar.
https://www.engineeringtoolbox.com/air-temperature-pressure-density-d_771.html
You will note that pressures are much higher than "perfect gas" laws are suggesting.
Well, air is not perfect and no other gas is but perfect gas laws are working well in low pressure range and above so called "critical temperature" above which gas cannot be liquified.

 

[sophiecentaur]

So rocky surface of Jupiter if made of common materials known on Earth would simply dissipate in gas and float

Could you elaborate on that and explain why?

 

[Martin0001]

Could you elaborate on that and explain why?

Any loose bits would be lifted up upon disturbance, as a result of interaction with atmosphere, erosion, "chipping" etc.
Because gas around would be denser, any loose chips would "fly up", until entire body is dissipated into chips floating in density equilibrium zone, eg at the depth where density of gas and density of rock are equal.
Such rocky core would also not be in a centre of Jupiter, because denser gas (or degenerate matter made of metallic hydrogen if one is there) would preferentially occupy this place.

 

[Kebil]

Because air pressure is uniformly distributed, there is no net force in any particular direction. As long as the density of gas is lower than that of the solid, the gas will simply move out form under that mass, as the movement of the mass down would otherwise increase the pressure under itself, and a gas at higher pressure will move to equalize pressure.

 

[Borek]

Any loose bits would be lifted up upon disturbance, as a result of interaction with atmosphere, erosion, "chipping" etc.
Because gas around would be denser, any loose chips would "fly up", until entire body is dissipated into chips floating in density equilibrium zone, eg at the depth where density of gas and density of rock are equal.
Such rocky core would also not be in a centre of Jupiter, because denser gas (or degenerate matter made of metallic hydrogen if one is there) would preferentially occupy this place.

Do you have any source for that, or are you just speculating?

 

[Martin0001]

Because air pressure is uniformly distributed, there is no net force in any particular direction. As long as the density of gas is lower than that of the solid, the gas will simply move out form under that mass, as the movement of the mass down would otherwise increase the pressure under itself, and a gas at higher pressure will move to equalize pressure.

Who said that air pressure is uniformely distributed?
If on Earth it is not then why on Jupiter should be otherwise?
We are also discussing situation where gas density is *higher than that of a solid*.

 

[Martin0001]

Do you have any source for that, or are you just speculating?

Fore any core to be there material of core would need to be of higher density than density of surrounding gas.
Less dense material would float on this gas .
So normal, Earth like minerals wouldn't wash as at pressures present in interiors of Jupiter gas would have higher densities.

 

[jbriggs444]

So normal, Earth like minerals wouldn't wash as at pressures present in interiors of Jupiter gas would have higher densities.

Have you Googled for the density of Jupiter?

 

[sophiecentaur]

Are you talking in terms of 'dust storms'? I guess that could account for the interface and some surface erosion of the outer core but the overall profile of densities would surely be decreasing with distance from the centre.
I am not sure whether Metallic Hydrogen would be more dense than iron etc.. Why should it be?

 

[Martin0001]

Have you Googled for the density of Jupiter?

Yes,
It is about 1.3g/cm3,
However this is an average density.
Density of interior should be much greater due to immense pressure there.
Average density on Earth rock is ~2.5g/cm3

 

[Borek]

Fore any core to be there material of core would need to be of higher density than density of surrounding gas.
Less dense material would float on this gas .

I know Archimedes principle, that's not what I asked for.

So normal, Earth like minerals wouldn't wash as at pressures present in interiors of Jupiter gas would have higher densities.

No doubt the gas gets dense, but as we are talking about GPa pressures and thousands of K temperatures, do you have any sources that will allow you to treat these "normal, Earth like minerals" as if they were what they are in normal conditions? In high pressures ice (different forms) density goes up to over 2 g/mL, I would expect other solids to get denser as well.

 

[Martin0001]

Yes, many things might be there but initial results of Juno mission are not supporting solid Earth like core:
https://www.zmescience.com/space/juno-mission-jupiter-26052017/
Talks are about fuzzy (dispersed) core or no core at all.

 

[Borek]

Took me some searching, the article you linked to doesn't go into details about the core (other than "rather liquid hydrogen than iron"). What I finally found (at http://onlinelibrary.wiley.com/doi/10.1002/2017GL073160/full ):

dilute core, with the heavy elements dissolved in hydrogen and expanded outward through a portion of the planet

suggests a homogeneous mixture ("dissolved" sounds more like a solution than slurry/suspension).

 

[sophiecentaur]

I re-read the thread title for the nth time and suddenly a picture of a Whoopy Cushion came to mind.

 

[Martin0001]

Took me some searching, the article you linked to doesn't go into details about the core (other than "rather liquid hydrogen than iron"). What I finally found (at http://onlinelibrary.wiley.com/doi/10.1002/2017GL073160/full ):
suggests a homogeneous mixture ("dissolved" sounds more like a solution than slurry/suspension).

Yes, have red few articles, gave a reference to one of them.
I was tempted to put arguments earlier on that metallic type of core would dissolve in another metal (metalic hydrogen) but you could place counterargument that under considerable gravity such solution (liquid alloy) would be unstable and heavier elements should still precipitate in the center.
Interesting subject is about minerals there. "Normal" chemistry should no longer be possible under such pressures so some exotic *inner shell chemistry* involving deeper electron orbitals should be at play.
I suspect that much more is to be learned about interiors of Jupiter and existing theories are opened for revision.
Here they claim that core is "fuzzy", partially dissolved, whatever word "fuzzy" may mean in this context.
https://spaceflightnow.com/2017/05/...-first-trove-of-data-from-nasas-juno-mission/
BTW, most of proper scientific articles is now behind a paywall, hence not accessible for someone no longer in academia/high tech industry (unless he wish to spend rather signifcant amount of money while checking references etc).

@sophiecentaur, thread went off title topic but OP did mention Jupiter related issues, eg landing on it in this context. Sometimes I do wonder why peoples are obsessed about issues like
1. Landing on Jupiter
2. Standing on neutron star
3. Falling through event horizon (they often ask what if legs are below and head above - is it possible to still climb up?)
4. How you would feel/what would you see from Earth if Sun gone supernova