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#### Fallingstar1971

##### Guest
Could someone direct me to a site where I can learn what formulas are needed to answer the following questions?

1. How dense would the atmosphere on Mars need to be to hold liquid water without it instantly boiling?

2. Is Mars massive enough to hold onto said atmosphere?

3. If it were possible, and Mars could retain water, would the atmosphere be too dense or heavy for humans to survive?

On an unrelated note:

Bodes Law

If the solar system followed Bodes Law perfectly, then would gravitational resonances tear the solar system apart?

Thanks in advance. You guys don't need to crunch the numbers if you don't want to, but I would like to learn the formulas if you don't mind sharing.

Star

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#### theridane

##### Guest
You can get all you need from Wikipedia and all the numbers from Wolfram Alpha. Here's what I got:

1. Not gonna happen. Water's phase diagram indicates that at Martian -50ish °C there's no liquid water going on no matter how much you squeeze it. If however the denser atmosphere raised the temperature a little bit (and chances are it would), you could pull it off with as little as 1 °C and 1 kPa (that's the current Mars surface pressure). All it really needs is a couple dozen degrees Celsius to turn it into a primordial paradise.

2. All planets are losing their atmospheres at some rate. Strong magnetic fields and deep gravity wells help reduce it, and Mars has neither. Atmosphere loss happens when heated molecules of gas in the upper atmosphere exceed the planet's escape velocity (among many other methods such as solar wind stripping, which would be prevented by a magnetic field). In a given volume of gas at a given temperature there's always a happy molecule that gets just the right amount of kicks in the right direction and escapes. The hotter the gas is, the more molecules get to reach highway speeds. The lighter the molecule is, the faster it goes with the same amount of energy (because kinetic E = 1/2 * m * v²). That's why hydrogen is always the first to go*. See Maxwell–Boltzmann distribution to calculate the probabilities.

3. At 1 kPa the atmosphere is still closer to a vacuum than to a marketable atmosphere and all humans would need protective gear to thrive. Some primitive plants (think algae) and single-celled organisms should do fine. If the pressure were a little higher, say 30 kPa (about 1/3 of Earth's), the most bad-ass high-altitude mountain climbers would be able to survive with breathing equipment (Chuck Norris without it).

* that's by the way how Mars might have lost its water - first its mag field went away, ionizing radiation got in, split water molecules into hydrogen and oxygen and hydrogen got vented into deep space

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#### Fallingstar1971

##### Guest
Why thank you. I would have done the legwork myself, but your work is appreciated. I will check out that data a bit later when I have more time

Thanks again

Star

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#### robnissen

##### Guest
theridane":fwuc8bzy said:
You can get all you need from Wikipedia and all the numbers from Wolfram Alpha. Here's what I got:

1. Not gonna happen. Water's phase diagram indicates that at Martian -50ish °C there's no liquid water going on no matter how much you squeeze it. If however the denser atmosphere raised the temperature a little bit (and chances are it would), you could pull it off with as little as 1 °C and 1 kPa (that's the current Mars surface pressure). All it really needs is a couple dozen degrees Celsius to turn it into a primordial paradise.

Actually during daylight during the summer, I believe the Martian temperature can get all the way up to a sweltering 50-60 degrees F.

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#### theridane

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It does (although Wiki and Wolfram Alpha state -5 °C to be the maximum for some reason), I used to joke about going to Cydonia for summer. But on a global scale the average temperature just doesn't support liquid water at this moment.

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#### robnissen

##### Guest
theridane":30rapnp7 said:
But on a global scale the average temperature just doesn't support liquid water at this moment.

But you cannot judge on a global scale. On a global scale, there is no ice on earth. You must look individually where water might be. And it appears that very briney water may be able to be liquid during summer days in some low lying areas of mars, if not under the current amounts of pressue, then with only very minor increases in pressure.

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#### theridane

##### Guest
Well I assumed the OP asked about Mars being able to have liquid water permanently, not just seasonally, since he asked about humans being in that atmosphere as well.

Localised (both spatially and temporally) pools of water could be possible assuming the temperatures were right. On Mars water needs to be between 0 and 6 °C in order to be liquid, anything lower and it goes solid (and ice sublimates pretty fast at 1 kPa), anything higher and it evaporates. That's pretty narrow if you ask me. Temperatures that specific are probably present only couple hours a day at best, going back way below zero at night. But it would be silly to draw conclusions without any data, there might be an equatorial oasis of "mostly liquid" water somewhere up there.

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#### yevaud

##### Guest
Bode's Law isn't actually a Law. It's simply a relationship, for which there isn't a good explanation.

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#### Fallingstar1971

##### Guest
Sorry guys, there seems to be a misunderstanding........

Let me put it another way......

Currently, "typical" H2O (say tap water) could not exist on the surface of Mars without instantly boiling away. If I understand this correctly, this is due to the lower pressures on Mars, and not the surface temperatures. I may have been mis-informed, but this was the "basis" for the question.

So, how does one go about increasing the pressure to the point where it doesn't boil away? One thought I had was to pile up some more atmosphere on Mars. I looked to Venus for that idea to to the tremendous pressures on the surface due to the weight of the atmosphere. I was thinking is Mars had a heavier atmosphere, then that would increase the pressure, and water could then exists comfortably on the surface.

Then I thought about Mars's size. Its much smaller and less massive than the Earth and to top it off, its magnetic field is shot. So with lower gravity, I was thinking the pressure would have to be higher than here on Earth, and that it may be outside the scope of where a human could survive without modest pressurized suit.

Sorry for being vague, it was just a curiosity. If people are going to colonize there someday they may need to know these things

Star

PS As far as Bodes Law, I know its bumkiss, but my curiosity was that if he was correct, would the solar system tear itself apart with gravitational resonances?

M

No

F

OK cool...thanks

Star

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#### robnissen

##### Guest
theridane":38cuby8t said:
Well I assumed the OP asked about Mars being able to have liquid water permanently, not just seasonally, since he asked about humans being in that atmosphere as well.

Localised (both spatially and temporally) pools of water could be possible assuming the temperatures were right. On Mars water needs to be between 0 and 6 °C in order to be liquid, anything lower and it goes solid (and ice sublimates pretty fast at 1 kPa), anything higher and it evaporates. That's pretty narrow if you ask me. Temperatures that specific are probably present only couple hours a day at best, going back way below zero at night. But it would be silly to draw conclusions without any data, there might be an equatorial oasis of "mostly liquid" water somewhere up there.

I don't think we are in disagreement here. I just don't like it when people make the categorical statement that there is no liquid water on Mars (and I'm glad to see that is not your position). We just don't know yet whether there is transiant liquid water on Mars. Hell, there may have been transient liquid water on the Phoenix lander. There is some evidence to support that Mars could support briney liquid water (remember your phase diagram was for pure water). And that briney liquid water, even if only liquid for a few hours during the summer, could be more than enough to keep a population of microbes fat, dumb and happy. Indeed, that microbe population could be the source of Mars methane. I an not a a member of the woo-woo crowd, it certainly has not yet been proven that there is extant life on Mars. But it also certainly has not been proven that there is no liquid water on Mars, such that life as we know it could not exist.

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#### theridane

##### Guest
You're right, brine is something I did not consider. That would widen the temperature range for life considerably. Indeed there is a plausible chance of brine water (doped with perchlorate salts) being on the Phoenix itself.

Can't wait for the MSL to hit the big ol' Red and do some digging. That rover's gonna be a blast. Just the hardware manifest makes me feel all fuzzy

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