Challenges of Terraforming Mars: Temperature, Air Pressure, and Radiation

[Nikitin]

What makes you think the density on the ground could be the same as Earth but the density in the outer layers could be higher?

Because Mars has a weak gravity. Extra gas would be needed to compensate for this. I.e. the air-pressure from above on the air below must compensate for the lack of gravity.

Well this is what I think is the reason

As for the "red colony book".. Kim Stanley has a degree in literature, not in any scientific subject.. This kind of ruins his credibility and thus the book for me :P

 

[Nirgal]

Because Mars has a weak gravity. Extra gas would be needed to compensate for this. I.e. the air-pressure from above on the air below must compensate for the lack of gravity.

Well this is what I think is the reason

As for the "red colony book".. Kim Stanley has a degree in literature, not in any scientific subject.. This kind of ruins his credibility and thus the book for me :P

Have you ever heard of the Genetic Fallacy? It's a type of argument or conclusion drawn from a person's background, origin, or history rather than the actual claims that the person makes. It is called a fallacy because it is an incorrect method of analysis.

If you read this book you'll see that Kim Stanley Robinson has done his research. What degree would you like him to have if you would feel better about reading it? Terraforming is a diverse interdisciplinary theoretical topic. There does not exist a degree that can cover every aspect.

As someone who has studied physics and has taken classes in planetary atmospheres and glacier physics, I think that he does an excellent job of portraying the science (that I am familiar with).

Also, its called science fiction. I still like Enders Game though I do not believe in faster-than-light communication.

 

[D H]

As someone who has studied physics and has taken classes in planetary atmospheres and glacier physics, I think that he does an excellent job of portraying the science (that I am familiar with).

That remark brings an xkcd comic to mind:

Physicists can be incredibly, well, dense, when it comes to fields that our outside their expertise. ryan_m_b has elaborated on the difficulties of developing an ecology. These concerns have been largely ignored. ryan and I have discussed the issue of the TRL 1 technologies hypothesized as terraforming mechanisms in this thread. These concerns have similarly been largely ignored.

Also, its called science fiction. I still like Enders Game though I do not believe in faster-than-light communication.

Right. And this site is about science, not science fiction.

Robinson did get one thing right in his books, and that is the Red movement. The underlying weltanschauung of this movement is in fact the current policy of NASA and supposedly of all of the nations that have signed the Outer Space Treaty. Probes sent to Mars are built under extreme clean room conditions, are sterilized prior to launch, and are exposed to vacuum and solar radiation during transit, all to avoid contaminating Mars -- and we still worry that we aren't doing enough. We do this just on the off chance that life might exist on Mars. All bets on terraforming Mars will be off should some probe find incontrovertible proof of life on Mars. The Red movement exists right now, and it has quite a bit of say on the NASA Advisory Council.

Speaking as a mentor:

This thread has been skating on very thin ice for quite some time per the PhysicsForums rules on overly speculative posts. Keep the posts real or this thread will be closed.[/color]

 

[Ryan_m_b]

Because Mars has a weak gravity. Extra gas would be needed to compensate for this. I.e. the air-pressure from above on the air below must compensate for the lack of gravity.

Well this is what I think is the reason

Huh? If you put gas on top of gas it doesn't sit there and push the lower gas down, it sinks into the lower gas. You can't have a higher density floating above a lower.

I agree with D H, the scientific problems with terraforming have been adequately outlined (along with a host of others), I don't see this thread as going anywhere productive if it starts citing science fiction.

 

[Nikitin]

Huh? If you put gas on top of gas it doesn't sit there and push the lower gas down, it sinks into the lower gas. You can't have a higher density floating above a lower.

I agree with D H, the scientific problems with terraforming have been adequately outlined (along with a host of others), I don't see this thread as going anywhere productive if it starts citing science fiction.

that was not what I meant :P I meant that the gas in the higher atmosphere of a terraformed Mars would have a higher density than the gas in the higher atmosphere of earth. at ground level they would have the same pressure.

sorry 4 my english

as for the book.. well sorry I just don't like science fiction. it's just a personal preference, sry.

 

[Ryan_m_b]

that was not what I meant :P I meant that the gas in the higher atmosphere of a terraformed Mars would have a higher density than the gas in the higher atmosphere of earth. at ground level they would have the same pressure.

In post 43 I said

I am unsure about how bad the radiation would be on Mars if there were a thick atmosphere, the atmosphere on Mars would have to be much thicker than that of Earth's to account for the face that Mars has a lower gravity. This means an equal amount of atmosphere would not cause the same pressure obviously necessary for life.

Leading on from this the atmosphere engineering of Mars could have much harder problems to solve, if the atmosphere needs to be 3x thicker to provide the same pressure then we may have problems with the amount of radiation absorbed. In addition martian weather systems could be drastically different from Earth's if the atmosphere was much denser, how this would effect the ecology would have to be carefully considered.

I am aware that we would need three times as much gas to produce the same pressure at ground level but you said in post 56

Anyway, I don't think the molar density of the air close to the surface of a completely terraformed Mars would be particularly higher than on earth.

There is a difference between air pressure and molar density. On Mars we would need 3 times as much atmosphere for the same pressure. You post at 56 suggested that this would not change the molar density at ground level, I'm interested to know how you came to this conclusion?

I may be wrong but if we have a column of air in a tube on Earth and exactly the same amount of air in a tube on Mars there will be more pressure at the bottom of the Earth tube (because gravity is higher). This is the same as if I had a 100kg weight on my head on Earth it would be putting 3x more pressure on my head than on Mars. To compensate for this lack of pressure 3x as much atmosphere is needed but would this not create a higher molar density on Mars? I would suggest yes (which would have dramatic effects on life) unless the atmosphere on Mars was spread out 3x further from the planet. I'd be interested to know if I am right or wrong here.

 

[PAllen]

Why would this be?

I think the supposition is based on the differential equation for pressure of column of gas as:

dP/dr = density*G*M/r^2

Then, further assuming temperature and composition are constant, density is proportional to pressure. Then, for mars, GM/r^2 at surface (surface gravitational acceleration) is lower than for earth; thus at given pressure, dp/dr will be lower than for earth. Thus, if pressure at surface matches earth, pressure and density above surface will higher (slower rate of decline).

Big flaw: even if you assume T and P are the same on the surface of Mars as for earth, there is absolutely no reason to believe that T as a function of altitude will be the same, let alone constant. Further, one expects composition to vary with altitude. However, I wouldn't be surprised of the broad conclusion were true: that matching P and T at the surface will lead to higher density at given altitudes compared to earth.

(To clarify the more complex realistic case, P = density * specific gas constant * T. Realistically, both T and specific gas constant (which is dependent on composition) vary with altitude).

 

[Ryan_m_b]

I think the supposition is based on the differential equation for pressure of column of gas as:

dP/dr = density*G*M/r^2

Then, further assuming temperature and composition are constant, density is proportional to pressure. Then, for mars, GM/r^2 at surface (surface gravitational acceleration) is lower than for earth; thus at given pressure, dp/dr will be lower than for earth. Thus, if pressure at surface matches earth, pressure and density above surface will higher (slower rate of decline).

Big flaw: even if you assume T and P are the same on the surface of Mars as for earth, there is absolutely no reason to believe that T as a function of altitude will be the same, let alone constant. Further, one expects composition to vary with altitude. However, I wouldn't be surprised of the broad conclusion were true: that matching P and T at the surface will lead to higher density at given altitudes compared to earth.

(To clarify the more complex realistic case, P = density *specific gas constant * T. Realistically, both T and specific gas constant (which is dependent on composition) vary with altitude).

So I would take that to mean in theory it could be the same as Earth but in practice no? The only thing I am struggling with is why there may be higher density at given altitudes but not at ground level?

 

[PAllen]

So I would take that to mean in theory it could be the same as Earth but in practice no? The only thing I am struggling with is why there may be higher density at given altitudes but not at ground level?

Under the simplistic assumption of constant temperature and composition you have (from the equations I gave before):

dP/dr = P * a / b

where b = (specific gas constant * T), and a = acceleration of gravity. So if you match P at the surface of Mars with P at Earth's surface, dP/dr will be smaller because 'a' is smaller. This means the rate of decline of pressure with altitude will be smaller than earth. Under the same simplistic assumptions, the density will also decline slower with altitude than Earth (and will match at the surface).

While constant composition and temperature are absurd, I suspect the broad conclusion would remain true. However, while ideal gas theory is physics, so I know a bit, the way temperature and composition would realistically change with altitude in the two cases (one hypothetical) is atmospheric science about which I know next to nothing.

 

[Nikitin]

In post 43 I said
I am aware that we would need three times as much gas to produce the same pressure at ground level but you said in post 56
There is a difference between air pressure and molar density. On Mars we would need 3 times as much atmosphere for the same pressure. You post at 56 suggested that this would not change the molar density at ground level, I'm interested to know how you came to this conclusion?

I may be wrong but if we have a column of air in a tube on Earth and exactly the same amount of air in a tube on Mars there will be more pressure at the bottom of the Earth tube (because gravity is higher). This is the same as if I had a 100kg weight on my head on Earth it would be putting 3x more pressure on my head than on Mars. To compensate for this lack of pressure 3x as much atmosphere is needed but would this not create a higher molar density on Mars? I would suggest yes (which would have dramatic effects on life) unless the atmosphere on Mars was spread out 3x further from the planet. I'd be interested to know if I am right or wrong here.

Hmm, well, at ground level the pressure and thus the molar density (assuming 99% of the air is nitrogen/oxygen) would be the circa same (molar density is dependent on pressure n temperature) as on Earth.

However, to get this identical ground level pressure on a low-gravity planet you'd need to have something compensating for the gravity - and that is the air above the ground-level air. The air above would be pushing the ground level air down - and we'd need more of it on Mars than on Earth to compensate for the weak Martian gravity.

EDIT: And yeh, while I'm making quite the assumptions, ignoring that the temperature decline on the Martian atmosphere will be quite different than that on earth, I don't see why my assumption is necessarily false, though. And I wouldn't mind at all if people would prove me wrong :D

 

[PAllen]

I think I have a good plausibility argument that Nikitin is right that:

If conditions on Mars surface were made to match Earth surface (temperature, pressure, composition), then density at higher altitudes on Mars would be greater, under reasonable assumptions.

I think we can agree there is no reason for significant composition change in the lower atmospheric levels. Then, I can derive from the ideal gas equations I've given that the only way for density on Mars at higher altitudes to match or be lower than on Earth is for temperature to increase with altitude (or possibly decline much slower than on earth). I think this is implausible. Therefore, if surface conditions match, Mars will have higher density atmosphere than corresponding altitudes on Earth (but still lower than on the ground).

 

[Ryan_m_b]

EDIT: And yeh, while I'm making quite the assumptions, ignoring that the temperature decline on the Martian atmosphere will be quite different than that on earth, I don't see why my assumption is necessarily false, though. And I wouldn't mind at all if people would prove me wrong :D

How about the significantly lower level of energy from the sun (both due to distance and smaller surface area), different surface albedo and different specific heat of the Martian surface (think of how much heat the oceans absorb).

For terraforming this would make a bit of a chicken and egg situation; the atmosphere is going to behave differently because of it's heat. To change the heat you are going to need more greenhouse gases, add oceans and build a biosphere. But to do those (especially the last) will require you to have an atmosphere.

 

[Nikitin]

Well, I don't know about that, but Mars' temperature would remain much more constant than Earth's due to the temperature being much more dependent on insulation of the planet instead of the Sun.. This would result in much less extreme weathers, wouldn't it?

Anyway, the atmosphere would at first be made up of almost exclusively carbondioxide gas. It would take a looong time after creating the atmosphere to actually engineer it to resemble Earth's. This stuff would happen very gradually so probably there will be plenty of time to think about this.

 

[Nikitin]

I think I have a good plausibility argument that Nikitin is right that:

If conditions on Mars surface were made to match Earth surface (temperature, pressure, composition), then density at higher altitudes on Mars would be greater, under reasonable assumptions.

I think we can agree there is no reason for significant composition change in the lower atmospheric levels. Then, I can derive from the ideal gas equations I've given that the only way for density on Mars at higher altitudes to match or be lower than on Earth is for temperature to increase with altitude (or possibly decline much slower than on earth). I think this is implausible. Therefore, if surface conditions match, Mars will have higher density atmosphere than corresponding altitudes on Earth (but still lower than on the ground).

Hmm, yes, what you speak is true. If the temperature would be high throughout the Martian atmosphere then things would be different in the way that the pressure would fall quite slowly as we move up the atmosphere. This would mean that there wouldn't be much need for the extra gases if the temperature could be kept reasonably high throughout the Martian atmosphere..

hmm couldn't this be easily achieved with the use of greenhouse gases?

 

[Drakkith]

I saw earlier in this thread that enough CO2 to thicken the atmosphere sufficiently was already present on Mars as Dry Ice. Is this true?

 

[Ryan_m_b]

I saw earlier in this thread that enough CO2 to thicken the atmosphere sufficiently was already present on Mars as Dry Ice. Is this true?

According to wiki 95% of Mars's atmosphere is CO2 and during winter the poles become covered in dry ice, this sublimes during spring. So the answer seems to be no, there are no extra stocks of dry ice waiting to be sublimed because the dry ice comes from the atmosphere anyway.

 

[Nikitin]

What no! some of the dry ice gets transformed into CO2 during the summer. The vast majority stays frozen.

There is also allot of CO2 in the soil.

If we could heat the planet 5-6 degrees then we'd get a proper atmosphere with proper pressure

 

[Ryan_m_b]

What no! some of the dry ice gets transformed into CO2 during the summer. The vast majority stays frozen.

There is also allot of CO2 in the soil.

If we could heat the planet 5-6 degrees then we'd get a proper atmosphere with proper pressure

Nikitin, as per the PF rules that you agreed to when you signed up it is not enough to simply claim someone is wrong before making your own claim. You need a reference to back you up.

You may very well the right, a quick wiki search did not confirm to me what you have said is true however if you have a citation from a reliable source I would be more than happy to read it.

 

[Nikitin]

http://en.wikipedia.org/wiki/Terraforming_of_Mars see carbondioxide sublimation

 

[Ryan_m_b]

http://en.wikipedia.org/wiki/Terraforming_of_Mars see carbondioxide sublimation

Hmm clicking on the link that that part of the wiki references takes us to this national http://channel.nationalgeographic.c...th-4588/living-on-mars#tab-living-on-mars/10" which itself has no links to published data showing where it got it's information from, it also doesn't say the same thing that the wiki article does. Just googling the 300millibar line from wiki brings up page after page that seem to take the info from wikipedia.

Earlier I did a trawl through various sources to try and find where this claim comes from but found nothing. If you could provide a link to peer-reviewed studies I would be happy to read it, the only research I could find just reiterated the fact that dry ice accumulates in winter and that there is carbon dioxide in Martian soil. I started at http://www.sciencedirect.com/" and searched for various terms such as carbon dioxide/dry ice/mars soil/mars atmosphere etc.

EDIT: I've found one paper that says

The released carbon dioxide will increase the atmospheric pressure and further warm the planet by creating a runaway greenhouse effect. Estimates of the amount of this carbon dioxide vary from 2 to 200 kPa (20–2,000 mbar), but for purposes of planetary ecosynthesis an intermediate amount of 10–40 kPa (100–400 mbar) would be adequate for the early stages.

Frustratingly it has no references for this though. I am also highly sceptical of the veracity of this paper as it chooses atmospheric pressures that the authors hypothesise could exist on Mars and then presents life on Earth that grow on mountains whilst merely paying lip service all the other problems of providing for this life (correct soil, light etc). Like most other terraforming papers this one has no real or concrete science, instead it takes data and suggests "perhaps this is possible". Whilst true without a far better understanding of how to build complex ecosystems statements along the lines of "if we get pressure X we could drop in plant Y and grow Y forests" are no very helpful.

 

[D H]

I have made multiple requests that this thread stay in line with PhysicsForums standards.

That hasn't happened, so thread closed.