Low Gravity?

[Ftiafpi]

One thing I always wondered is how is it possible to have lower gravity yet higher air density. Wouldn't lower gravity mean the air would disperse into a higher altitude atmosphere, thereby lowering the density?

[Eyawng te Klltepayu]

One thing I always wondered is how is it possible to have lower gravity yet higher air density. Wouldn't lower gravity mean the air would disperse into a higher altitude atmosphere, thereby lowering the density?

If the mass of atmosphere per unit area (think of a column extending up from the surface) were the same as on Earth, then yes, the density and air pressure at the surface would be lower.
The atmosphere would have to be greater in mass than ours per unit area in order to produce the stated parameters. This is certainly possible and there are examples of this in our own solar system. Venus and Titan both have lower gravity and higher air density than Earth.

Pandora having a lower gravity than Earth would also mean that the scale height would be greater.

Also: Wou! You have 3000 posts!

[kewnya txamew'itan]

One thing I always wondered is how is it possible to have lower gravity yet higher air density. Wouldn't lower gravity mean the air would disperse into a higher altitude atmosphere, thereby lowering the density?

If the mass of atmosphere per unit area (think of a column extending up from the surface) were the same as on Earth, then yes, the density and air pressure at the surface would be lower.

Just to add clarification about how this could be possible, having significantly more atmosphere wouldn't work as most of the excess would bleed off into space IIRC however if the makeup is different and has a mean relative formula mass significantly large than that of earth's air (as indeed Pandora does), that could increase the density to the level we expect.

[Eyawng te Klltepayu]

The bleed off times are pretty long, even for low mass bodies like the Moon. I think I remember reading somewhere that if we were to give the Moon an extensive atmosphere that could reproduce standard sea-level terrestrial conditions on the lunar surface that atmosphere would have a 'half life' of around 1 million years.

Of course, on a planetary timescale that's nothing.

a mean relative formula mass significantly large than that of earth's air (as indeed Pandora does), that could increase the density to the level we expect.

Yes, that extra CO2 comes in handy. Not that it matters but having mentioned scale height once before I should probably note that higher M would lower H.

[kewnya txamew'itan]

The bleed off times are pretty long, even for low mass bodies like the Moon. I think I remember reading somewhere that if we were to give the Moon an extensive atmosphere that could reproduce standard sea-level terrestrial conditions on the lunar surface that atmosphere would have a 'half life' of around 1 million years.

Of course, on a planetary timescale that's nothing.

Or indeed on a lunar timescale. If Pandora's atmosphere was dense solely because it had started off with a huge amount of gas in its atmosphere it would have to be far too young to have evolved life independently or else started with a ludicrous amount gas.

[Eyawng te Klltepayu]

Or indeed on a lunar timescale. If Pandora's atmosphere was dense solely because it had started off with a huge amount of gas in its atmosphere it would have to be far too young to have evolved life independently or else started with a ludicrous amount gas.

Natural satellites are planetary bodies even though they aren't planets. The use of this adjective to describe the Moon is valid.
I was not implying that Pandora's atmosphere is a remnant of something more extensive, just noting in passing that the bleed off times are slow on human timescales.

[kewnya txamew'itan]

Or indeed on a lunar timescale. If Pandora's atmosphere was dense solely because it had started off with a huge amount of gas in its atmosphere it would have to be far too young to have evolved life independently or else started with a ludicrous amount gas.

Natural satellites are planetary bodies even though they aren't planets. The use of this adjective to describe the Moon is valid.
I was not implying that Pandora's atmosphere is a remnant of something more extensive, just noting in passing that the bleed off times are slow on human timescales.

No worries, I got that, I was just clarifying for anybody else reading this that your comment about planetary timescales does still apply.

[Kätsyín te Zotxekay Tsyal’itan]

With that explination my mind has just been blown...

[Duma Vadamee {Aungia Tsawkeyä}]

second that...

[Toruk Makto]

There is supposedly a much higher fraction of CO2 and xenon on Pandora. Those gases are much heavier than the nitrogen that Earth has. Thus even in lower gravity, the air pressure would be 1 atmosphere or more. Of course the pressure would fall off with altitude faster, so the floating mountains may have much lower pressure than was apparent in the film.

[Ikran Ahiyìk]

So that the ikrans can fly

[Eyawng te Klltepayu]

Of course the pressure would fall off with altitude faster, so the floating mountains may have much lower pressure than was apparent in the film.

There was some discussion of this previously. A higher M (mean molecular mass of dry air) will lower H (the scale height), but a lower g will raise it. Knowing whether the scale height is larger or smaller than Earth's will require a quantitative description of the composition of the air, something we don't yet have. I think we could make a reasonable guess at T, the mean planetary surface temp.

[Toruk Makto]

Lower G will reduce the density gradient. Given the scale of Pandora, the mountains look like they are perched way up there...

[Duma Vadamee {Aungia Tsawkeyä}]

every one knows that all the animals, and Na'vi, have hallow carbon fiber bones right? that might be a product from low gravity....or not. I dont really know.

[Ekirä]

every one knows that all the animals, and Na'vi, have hallow carbon fiber bones right? that might be a product from low gravity....or not. I dont really know.

AFAIK their bones aren't hollow, just reinforced with carbon fiber.

....and they have bones reinforced with naturally occurring carbon fiber. They are very hard to kill.

[Meynari Ke'nawm]

The atmosphere is denser. The ikran have to have special muscles and slits is their wings. There is a whole article on it on a bunch of Avatar wikis. But, Pandora is slightly smaller than Earth, so there's less gravity, right? But, with the denser atmosphere, wouldn't it even out? Plus, there is no seen effect in the movie, other than Quaritches' comment. It's not like the people float around.

P.S. If you have ever watched WALLE, have you seen what the absolute lack of gravity does to them? (that, and sitting in chairs for their whole life) I would say they are all pretty soft and bulgy!

[Human No More]

Atmospheric density wouldn't offset a lower gravity. Indeed, it's the other reason ikran and toruk are capable of flying as well as they are as it means they generate more lift (although need greater strength than they otherwise would).

[Kätsyín te Zotxekay Tsyal’itan]

Atmospheric density wouldn't offset a lower gravity. Indeed, it's the other reason ikran and toruk are capable of flying as well as they are as it means they generate more lift (although need greater strength than they otherwise would).

Actually, it would. At least as far as the movie goes, there is a cut-out scene where Jake and Grace report to Selfridge while he is driving golf balls and he mentions something about air density off-setting the low gravity.

['Oma Tirea]

Atmospheric density wouldn't offset a lower gravity. Indeed, it's the other reason ikran and toruk are capable of flying as well as they are as it means they generate more lift (although need greater strength than they otherwise would).

Actually, it would. At least as far as the movie goes, there is a cut-out scene where Jake and Grace report to Selfridge while he is driving golf balls and he mentions something about air density off-setting the low gravity.

Srane...

Spoiler

You see, it's the damn pack... the high air density and the low gravity cancel out which doesn't affect the...

[Human No More]

In terms of the air resistance being higher, against the increased shot power. The physics of an unpowered object on a ballistic trajectory and of a flying creature are completely different things. Both the lower gravity AND the increased air density work in Toruk, ikran, etc.'s favour.