# Thread: Density of air (Gas) question

1. I hope this is the right section. Please bear in mind that I don't have the first inkling of physics and/or chemistry. So, I'm sorry if I ruffle some feathers () with this question

I've wondered for a while if there is a type/state of gas/air that humans may be able to walk on. Specifically, Jupiter is a giant ball of gas and the pressure is huge there. I understand that if humans were able to get to Jupiter (and other such gas giants) that there would be nothing to land on because there is no surface, but I also understand that as you get closer to the core everything becomes much more dense... Assuming we could with stand the crushing pressure, would there be a point that the air would become so dense that it would act like "ground" and we could stand on it?

AND If dense air can act like a solid is it possible that one day in the future we could build structures that would sit atop that dense gas and extend into the upper atmosphere of Jupiter or Saturn and make inhabiting gas giants a viable option?

Thank you.

2.

3. If the gas were so dense that it acted like a solid then it would be ... a solid!

4. Originally Posted by grmpysmrf
I hope this is the right section. Please bear in mind that I don't have the first inkling of physics and/or chemistry. So, I'm sorry if I ruffle some feathers () with this question

I've wondered for a while if there is a type/state of gas/air that humans may be able to walk on. Specifically, Jupiter is a giant ball of gas and the pressure is huge there. I understand that if humans were able to get to Jupiter (and other such gas giants) that there would be nothing to land on because there is no surface, but I also understand that as you get closer to the core everything becomes much more dense... Assuming we could with stand the crushing pressure, would there be a point that the air would become so dense that it would act like "ground" and we could stand on it?

AND If dense air can act like a solid is it possible that one day in the future we could build structures that would sit atop that dense gas and extend into the upper atmosphere of Jupiter or Saturn and make inhabiting gas giants a viable option?

Thank you.
Regarding Jupiter, there does not appear to be a solid phase at all, as the dominant gases in the Jovian atmosphere and H and He, which remain above their triple points even at low altitudes: Atmosphere of Jupiter - Wikipedia, the free encyclopedia

The distinctive nature of a solid phase is that the molecules are in fixed positions, so the substance cannot flow. This is what gives a sold surface its resistance when we tread on it. Above the triple point all you have is a supercritical fluid. This can be as dense as a solid but as the molecules can move, it flows and you can't walk on it.

5. So, if I understand you correctly Exchemist, it doesn't matter how dense a gas is or becomes it will never be dense enough to act as a solid?

6. Originally Posted by grmpysmrf
So, if I understand you correctly Exchemist, it doesn't matter how dense a gas is or becomes it will never be dense enough to act as a solid?
Not if it remains a fluid, because a fluid is not a solid.

As to whether it becomes a solid under pressure or not, the important thing is whether the substance is above or below its triple point. This is the point on the phase diagram for the substance where the lines showing how the melting and boiling points vary with pressure and temperature meet. There's an example of a phase diagram of helium here, if you scroll down a bit(and ignore the irritating computer-generated invitations of help):Phase Change Diagram, CO2 Phase Diagram | Chemistry@TutorVista.com

You can see the solid only exists at a combination of very high pressure AND very low temperatures, lower than those that exist on Jupiter. But with methane, say, higher up the page, you can get a solid under more moderate conditions. It all depends on the substance - and in particular the strength of the intermolecular forces that hold the molecules in place in the solid state. Not surprisingly, these forces are extremely weak with He, hence the solid only forms at extremely cold temperatures indeed, regardless of the pressure.

7. Originally Posted by exchemist
Originally Posted by grmpysmrf
So, if I understand you correctly Exchemist, it doesn't matter how dense a gas is or becomes it will never be dense enough to act as a solid?
Not if it remains a fluid, because a fluid is not a solid.

As to whether it becomes a solid under pressure or not, the important thing is whether the substance is above or below its triple point. This is the point on the phase diagram for the substance where the lines showing how the melting and boiling points vary with pressure and temperature meet. There's an example of a phase diagram of helium here, if you scroll down a bit(and ignore the irritating computer-generated invitations of help):Phase Change Diagram, CO2 Phase Diagram | Chemistry@TutorVista.com

You can see the solid only exists at a combination of very high pressure AND very low temperatures, lower than those that exist on Jupiter. But with methane, say, higher up the page, you can get a solid under more moderate conditions. It all depends on the substance - and in particular the strength of the intermolecular forces that hold the molecules in place in the solid state. Not surprisingly, these forces are extremely weak with He, hence the solid only forms at extremely cold temperatures indeed, regardless of the pressure.
Thank you. I think I understood some of that.

8. Originally Posted by grmpysmrf
Originally Posted by exchemist
Originally Posted by grmpysmrf
So, if I understand you correctly Exchemist, it doesn't matter how dense a gas is or becomes it will never be dense enough to act as a solid?
Not if it remains a fluid, because a fluid is not a solid.

As to whether it becomes a solid under pressure or not, the important thing is whether the substance is above or below its triple point. This is the point on the phase diagram for the substance where the lines showing how the melting and boiling points vary with pressure and temperature meet. There's an example of a phase diagram of helium here, if you scroll down a bit(and ignore the irritating computer-generated invitations of help):Phase Change Diagram, CO2 Phase Diagram | Chemistry@TutorVista.com

You can see the solid only exists at a combination of very high pressure AND very low temperatures, lower than those that exist on Jupiter. But with methane, say, higher up the page, you can get a solid under more moderate conditions. It all depends on the substance - and in particular the strength of the intermolecular forces that hold the molecules in place in the solid state. Not surprisingly, these forces are extremely weak with He, hence the solid only forms at extremely cold temperatures indeed, regardless of the pressure.
Thank you. I think I understood some of that.
Oh dear, seems I didn't do a very good job of explaining. Perhaps the excursion into phase diagrams was a bridge too far.

But at any rate are you OK now with the distinction between a dense fluid and and a solid of equal density? Mercury is a good example of a very dense substance that is fluid (liquid in this case). You couldn't stand on it, but you would float very high in a bath of it. You'd bob about the surface like a cork on water.

9. We tell to those whom ask of such questions that a cup full of Jupiter would float on water here on Earth..
~ It would actually just disperse as the gas it is, would. I think you do understand this.. At a greater depth the pressure of atmosphere rises to a point where such densaty would crush any living tissue and machine.
~ Even at the top of the atmosphere the gravity force proponent would not allow any life form I can imagine.. and then the radiated heat *It's a no.* Even a little away from that atmosphere and in a stable orbital path.. To much radiation for life as we know it.. The same story for Saturn also.. These Gas Giant Planets are just too big for us to go anywhere near.. Gravity, Pressure, Heat, and radiations..
~ But their moons are doable.. maybe..

10. Jovan gravity would flatten a human who was anywhere in its vacinity unless he was in orbit. Is it possible to make a balloon like device that would float in jovan atmospher? I don't think so. balloons work because they are filled with a "lighter than air" gas, hydriogen or helium. But the jovan atmospher is hydrogen. What could we fill a balloon with that would be lighter than that? Even if we could, the giant gravity would still affect the Balloon pilots and flatten theminto human panckes.

11. Originally Posted by Sealeaf
Jovan gravity would flatten a human who was anywhere in its vacinity unless he was in orbit. Is it possible to make a balloon like device that would float in jovan atmospher? I don't think so. balloons work because they are filled with a "lighter than air" gas, hydriogen or helium. But the jovan atmospher is hydrogen. What could we fill a balloon with that would be lighter than that? Even if we could, the giant gravity would still affect the Balloon pilots and flatten theminto human panckes.
But could one not make a sort of diving bell, able to resist the pressure at the altitude at which the density was sufficient to permit it to float? I had thought sea diving bells float, don't they, which suggest the strength of materials is enough for such a purpose?

But maybe you will yes, but at that altitude the gravity would crush a man flat on the floor, so he could not lift enough of his weight to fill his lungs, or something.

12. No, no, it's not like that. you did fine. I wrote that because there was quite a bit to understand.
Again, if I understood correctly from what you wrote and the graphs that the various gases have, there are different temps and pressures that allow gases to act as solid but it needs to be really cold and have a ridiculous amount of pressure forced on it.

Although with your follow up I'm not sure where the "fluid" came in. I'm talking strictly gas/air. Unless you're telling me that in order for a gas to act as a solid it first must become a type of liquid. Then I understand that too. And I'm disappointed.

When the wind pushes on me I want to have a way to climb it because it feels solid against my face. but it's not. So I was under the impression that if there was more pressure it may act as a kind of solid that could support us like a wall or a floor.

With regards to everyone else and the impossibilities of inhabiting Jupiter and Saturn, I understand the problems with crazy levels of radiation and the destructive power of immense pressure. I was strictly wondering how much pressure would need to exist before people were able to walk on air (yes, assuming all attributes in humans were the same except we'd found a way to construct a suit or modify our bodies that lets us be immune to pressure greater than found on earth.) However, exchemist has shown me it's more than just pressure that is needed if it it were even possible.

Originally Posted by exchemist
Originally Posted by grmpysmrf
Originally Posted by exchemist
Originally Posted by grmpysmrf
So, if I understand you correctly Exchemist, it doesn't matter how dense a gas is or becomes it will never be dense enough to act as a solid?
Not if it remains a fluid, because a fluid is not a solid.

As to whether it becomes a solid under pressure or not, the important thing is whether the substance is above or below its triple point. This is the point on the phase diagram for the substance where the lines showing how the melting and boiling points vary with pressure and temperature meet. There's an example of a phase diagram of helium here, if you scroll down a bit(and ignore the irritating computer-generated invitations of help):Phase Change Diagram, CO2 Phase Diagram | Chemistry@TutorVista.com

You can see the solid only exists at a combination of very high pressure AND very low temperatures, lower than those that exist on Jupiter. But with methane, say, higher up the page, you can get a solid under more moderate conditions. It all depends on the substance - and in particular the strength of the intermolecular forces that hold the molecules in place in the solid state. Not surprisingly, these forces are extremely weak with He, hence the solid only forms at extremely cold temperatures indeed, regardless of the pressure.
Thank you. I think I understood some of that.
Oh dear, seems I didn't do a very good job of explaining. Perhaps the excursion into phase diagrams was a bridge too far.

But at any rate are you OK now with the distinction between a dense fluid and and a solid of equal density? Mercury is a good example of a very dense substance that is fluid (liquid in this case). You couldn't stand on it, but you would float very high in a bath of it. You'd bob about the surface like a cork on water.

13. Although with your follow up I'm not sure where the "fluid" came in. I'm talking strictly gas/air.
Gases are classed as "fluids" too... Fluid - Wikipedia, the free encyclopedia Another example of a word that means different things in everyday language and as a scientific term...

14. Originally Posted by exchemist
Originally Posted by Sealeaf
Jovan gravity would flatten a human who was anywhere in its vacinity unless he was in orbit. Is it possible to make a balloon like device that would float in jovan atmospher? I don't think so. balloons work because they are filled with a "lighter than air" gas, hydriogen or helium. But the jovan atmospher is hydrogen. What could we fill a balloon with that would be lighter than that? Even if we could, the giant gravity would still affect the Balloon pilots and flatten theminto human panckes.
But could one not make a sort of diving bell, able to resist the pressure at the altitude at which the density was sufficient to permit it to float? I had thought sea diving bells float, don't they, which suggest the strength of materials is enough for such a purpose?

But maybe you will yes, but at that altitude the gravity would crush a man flat on the floor, so he could not lift enough of his weight to fill his lungs, or something.
Let's say you have a bathyscaphe capable of diving to a depth of Challenger Deep at 35,798 ft (10,911 m). This would be capable of withstanding 16,000 psi or about 110 Mpa.
If your bathyscaphe had a density of about 1 gram/cubic centimeter it would just sink in water. In order to float in hydrogen, it would have to sink to a level where the density of hydrogen is 1 gram/cc.
Hydrogen at 1 atmosphere is .08988 g/liter, or 8.99E-5 g/cc. If it acts like an ideal gas, it would require a pressure of 1/(8.99E-5) atmospheres to compress it to 1 gram/cc.
That's about 11,124 atmospheres, or 163,515 psi which is about 10 times what the vessel can withstand. I think that's correct.

15. Originally Posted by Harold14370
Originally Posted by exchemist
Originally Posted by Sealeaf
Jovan gravity would flatten a human who was anywhere in its vacinity unless he was in orbit. Is it possible to make a balloon like device that would float in jovan atmospher? I don't think so. balloons work because they are filled with a "lighter than air" gas, hydriogen or helium. But the jovan atmospher is hydrogen. What could we fill a balloon with that would be lighter than that? Even if we could, the giant gravity would still affect the Balloon pilots and flatten theminto human panckes.
But could one not make a sort of diving bell, able to resist the pressure at the altitude at which the density was sufficient to permit it to float? I had thought sea diving bells float, don't they, which suggest the strength of materials is enough for such a purpose?

But maybe you will yes, but at that altitude the gravity would crush a man flat on the floor, so he could not lift enough of his weight to fill his lungs, or something.
Let's say you have a bathyscaphe capable of diving to a depth of Challenger Deep at 35,798 ft (10,911 m). This would be capable of withstanding 16,000 psi or about 110 Mpa.
If your bathyscaphe had a density of about 1 gram/cubic centimeter it would just sink in water. In order to float in hydrogen, it would have to sink to a level where the density of hydrogen is 1 gram/cc.
Hydrogen at 1 atmosphere is .08988 g/liter, or 8.99E-5 g/cc. If it acts like an ideal gas, it would require a pressure of 1/(8.99E-5) atmospheres to compress it to 1 gram/cc.
That's about 11,124 atmospheres, or 163,515 psi which is about 10 times what the vessel can withstand. I think that's correct.
Ah yes of course, I hadn't thought about that. How silly. So it could never work with today's materials.

16. Originally Posted by PhDemon
Although with your follow up I'm not sure where the "fluid" came in. I'm talking strictly gas/air.
Gases are classed as "fluids" too... Fluid - Wikipedia, the free encyclopedia Another example of a word that means different things in everyday language and as a scientific term...
Thanks for the tip.

17. Its not just the pressure. We can shield ourselves from pressure. Its the gravity. We can't shield ourselves from the gravity.

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