Pack for a day trip to mars!

[KrazyHorse]

Originally posted by Geronimo
KH, do you know a way to calculate how much atmosphere a body with Mars's gravity could hold before it would start leaking off into space at an appreciable rate?

I could figure out a formula directly from statistical mechanical considerations but it would be a significant amount of work. I suggest you google it as I'm lazy.

[chequita guevara]

Originally posted by KrazyHorse
Actually, chegitz, the size of the body is the problem.

It's a problem, not the problem. Solar winds have a much bigger impact than body size. Even Pluto has an atmosphere, as well as Io and Titon, all of which are smaller than Mars.

But if we look at the surface features on Mars, one would likely conclude they had a more substantial atmosphere for a longer period of time than ten thousand years, at least one suficient enough for liquid water to exist.

[Spiffor]

Originally posted by chegitz guevara
But if we look at the surface features on Mars, one would likely conclude they had a more substantial atmosphere for a longer period of time than ten thousand years, at least one suficient enough for liquid water to exist.

Why necessarily liquid water It could have been anything.

[Geronimo]

Originally posted by KrazyHorse


I truly doubt it. You're welcome to try, though.

Might be possible for a couple of minutes. Not for an hour.

Assuming everything went perfectly you're still exerting yourself heavily to breathe in a strong pressure diffential with very very little oxygen while your lung tissue is slowly being ripped, your blood vessels are becoming badly swollen etc.

You're 50% above the safe limit of pressure differential at best. That's not very bright.

no exertion is required, the breathing can occur passively since the tank is at much higher than ambient pressure, both inhalation and exhilation can occur passively.

OTOH, I agree that however long such a low pressure environment might be endured, it will be a very gruelling experience (assuming you don't pass out). Furthermore damage suffered would likey be permanent alveolar damage resembling emphysema.

The blood vessels should deal with the pressure fairly easily but the resulting edema would certainly contribute to making the stay a memorably uncomfortable one.

[Geronimo]

Originally posted by KrazyHorse


Actually, chegitz, the size of the body is the problem. Mars would lose its atmospher something like 100 times faster than the Earth does if they had equivalent surface pressures (these are rough figures and I'm quoting them from a source I read something like 10 years ago, so they might be off).

So in addition to the fact that the Earth retains its atmosphere much better than Mars does, there is also the replenishment issue (the Earth replenishes its atmosphere at a much higher rate than Mars does too).

The difference between Venus and the Earth is solely due to the supply issue (there are geysers of sulfur dioxide etc. constantly being pumped out from the surface of venus at an incredible rate). Between the Earth and Mars it's due to both supply and loss.

As for the magnetic field slowing loss, it might have an effect, but the basic issue is one of diffusion. The smaller the potential well you trap the gas particles in the faster they escape.

geysers of sulfuric acid? that certainly makes sense and explains a lot but I didn't know that Venus had been verified to be geothermally active. Do you know when these geysers were discovered?

[KrazyHorse]

Pluto's atmosphere is there solely because the production rate is so high. Pluto's mainly frozen gases, which sublimate rapidly on the sunlit side. There are geysers constantly going on the surface. It loses its atmosphere much quicker than mars does.

Similarly with io . Io has ridiculously active volcanoes.

As for Titan, it's interesting you use that as an example, given that it has no magnetic field of its own and spends much of its time above Saturn's magnetosphere.

EDIT: Titan's dense atmosphere is considered something of a mystery, BTW...

[KrazyHorse]

Originally posted by Geronimo


no exertion is required, the breathing can occur passively since the tank is at much higher than ambient pressure, both inhalation and exhilation can occur passively.

How does exhalation occur, praytell? do you have to flip a switch every time you breathe?

[KrazyHorse]

Originally posted by Geronimo



geysers of sulfuric acid? that certainly makes sense and explains a lot but I didn't know that Venus had been verified to be geothermally active. Do you know when these geysers were discovered?

I was under the impression that this was the accepted theory. I have no clue if they've been directly observed or not. I'm also a physicist, not a planetary scientist, so this isn't my area of specialty.

[Geronimo]

Originally posted by KrazyHorse


80 mm Hg = 10 kPa

So we're 50% above that at least

That assumes the minimum oxygen level for survival and that we're operating in a 100% oxygen atmosphere.

the 300kg weight analogy doesn't seem right either. The pressure difference experienced by the aorta for example is on the order of 18 kPa and it's hard to imagine it would be equiped to hold back a 300kg weight.

My god. Force = pressure X area

The chest has a much larger area than the cross-section of the aorta. probably by a factor of 1000 or so. Thus for an equivalent pressure differential the chest experiences a force 1000 times greater.

Something doesn't seem to compute here. the chest wall is at least as thick relative to it's volume as the walls of the aorta are to their volume.

[Geronimo]

Originally posted by KrazyHorse


How does exhalation occur, praytell? do you have to flip a switch every time you breathe?

use a regulator (one way inflow and one way outflow valve)! That approach solved exactly the same problem in scuba diving. I think you knew that but just had momentary lapse of understanding.

of course the regulators for scuba are usually designed for a pressure differential only between the tank and the mouthpiece and not an additional differential between ambient and the mouthpiece the principal can be made to work in the same way.

[chequita guevara]

Originally posted by KrazyHorse
Pluto's atmosphere is there solely because the production rate is so high. Pluto's mainly frozen gases, which sublimate rapidly on the sunlit side. There are geysers constantly going on the surface. It loses its atmosphere much quicker than mars does.

Similarly with io . Io has ridiculously active volcanoes.

As for Titan, it's interesting you use that as an example, given that it has no magnetic field of its own and spends much of its time above Saturn's magnetosphere.

EDIT: Titan's dense atmosphere is considered something of a mystery, BTW...

Titan's also very far from the sun, so the solar winds are much weaker there.

As for Pluto bleeding off it's atmosphere much more quickly than Mars, no doubt. The point I'm trying to make is that it would have occured much more quickly if solar winds were as much of an issue there as they are in the inner Solar system.

[KrazyHorse]

Who said anything about thickness?

F = P X A

The aorta has a cross-sectional area of around 1 cm^2 (very rough estimate. The ribcage presents a forward area of something like 0.1 m^2 = 1000 cm^2

to create the lungs were to support a pressure differential of 22 kPa (pp O2 at sea level) they would need to be able to support 22 000 N/m * 0.1 m^2 = 2200 N = 250 kg weight pushing the ribcage outward.

[Geronimo]

Originally posted by chegitz guevara


Titan's also very far from the sun, so the solar winds are much weaker there.

As for Pluto bleeding off it's atmosphere much more quickly than Mars, no doubt. The point I'm trying to make is that it would have occured much more quickly if solar winds were as much of an issue there as they are in the inner Solar system.

i may be showing my ignorance of physics here, but wouldn't the biggest factor of all be the low temperature of the gasses in plutos atmosphere? Isn't the matter of whether the gas escapes just going to be a matter of whether a given gas molecule is moving faster than pluto's escape velocity? And won't that depend directly on the temperature of the gasses?

[KrazyHorse]

Originally posted by Geronimo


use a regulator (one way inflow and one way outflow valve)!

I'm aware of that concept. I simply doubt it would work very well when there's a very large standing pressure differential. There's probably a technical solution, but certainly not generally available...

[Sandman]

BTW, while we're at daydreaming about Mars, would it be theoritically possible to engineer a lifeform that could survive the pressure and the cold, while feeding off whatever the atmosphere/soil provides?

Well, the Martian summer would provide a modest growing season, but the low, low pressure means that liquid water can't exist. And that's a real problem for any sort of life.

As for terraforming, I think that the best you could hope for would be a somewhat thicker atmosphere - not suitable for breathing, but enough to limit the temperature flux, allow for some liquid water, and make surface dwellings cheaper to build (because they don't have to withstand a huge difference in pressure).