Odd question about terraforming Mars

[someone_else]

During a heated debate with a guy, the case of terraforming mars pops up.
So I go looking for proofs to back my theory.

And I read only essays (even from Zubrin, the would-be Emperor of Mars) on how adding carbon dioxide or other greenhouse gases (ammonia?) to make it hotter and have a thicker atmosphere.
Then they all talk to seed it and start rising the oxygen content.

Now, carbon dioxide tends to be lethal at even very low concentrations (5% in Earth pressure) and that means it must be far less than anything else in atmosphere even if you adjust a little the partial pressures.
And you cannot have a too oxygen-rich atmosphere or risk to burn down to ash everything for every spark you make.

So the projects I read may create life on Mars, but not a breathable atmosphere for us pink humies.

My question is: Am I missing something obvious?

[CSJM]

Apart from the lack of magnetic field being one of the reasons Mars can't hold a proper atmosphere, you're missing lots and lots of filler. Nitrogen makes up a large part of air on Earth, alongside a fair number of other gases. I'm not sure how would you go about pumping such volumes of nitrogen to Mars, but that's what you'll have to do to create an atmosphere that humans can breathe unaided.

Though if you ask me, I think properly terraforming Mars is impossible. Best you can do is make its atmosphere contain enough oxygen so that it can be extracted by a portable filter in a spacesuit. Then plants can grow all they want, nothing will explode, and people won't have to lug around oxygen tanks on the surface.

[someone_else]

Apart from the lack of magnetic field being one of the reasons Mars can't hold a proper atmosphere

Well, the solar wind isn't particularly fast in stripping away atmosphere on a human scale. Mars lost its atmo in orders of magnitude more time than it took the human civilization to go from chimp-like to today. (million years? hundred million years?)

The lack of magnetic field will mean even the shittiest space radiation will reach surface though.

you're missing lots and lots of filler. Nitrogen makes up a large part of air on Earth

Yup. that is the main problem I noticed. I haven't found papers talking about evidence of abundant nitrogen compounds on Mars (like ammonia) that can be cracked to make nitrogen relatively cheaply (cheaper than carting zillion tons of ammonia from asteroids/gas giants or stealing nitrogen from Titan).

And I don't know what else can be used as "buffer gas" other than He that will escape Mars gravity asap.

Best you can do is make its atmosphere contain enough oxygen so that it can be extracted by a portable filter in a spacesuit.

Yeah, that seems more or less where these studies are aimed at. But then selling it as "terraforming" sounds a little too much to me.

I also have some doubts about a gimmick being able to take oxygen and keep out carbon dioxide at the rates needed by human respiration being portable enough. They are two gas, and I can only think of fractional distillation methods to separate them.
But I'm nowhere near expert in rebreathers.

[CSJM]

And then there's the matter of pressure. With just a bit above a third of Earth's gravity, Mars would barely provide a "breathable" atmosphere even if it had all the necessary gasses in proportion. We could probably have humans adapt though, but I'm not sure how different a sea level pressure it'd end up being. I think we'd be much better off just thinking up good ways to make large colony structures. Maybe even out of clear materials, to see the sky and landscape and whatnot.

[Guardsman Bass]

There's a variety of inert, heavy gases that you could probably use, but I have no idea whether Mars has them in any decent amount locked up in rocks and so forth.

I also have some doubts about a gimmick being able to take oxygen and keep out carbon dioxide at the rates needed by human respiration being portable enough. They are two gas, and I can only think of fractional distillation methods to separate them.

I'm wondering about that as well. If you could get a relatively light mask that could separate them (think the masks from Avatar), then you could likely raise the fraction of the atmosphere that is CO2 up to the point where it gets the temperature to a fairly comfortable degree. I'm not personally fond of that option (since I'd prefer it if humans were able to breath unaided on terraformed Mars), but it's something.

The lack of magnetic field will mean even the shittiest space radiation will reach surface though.

Not necessarily. There would be more radiation than on Earth's surface, but a much thicker atmosphere would offer some protection as well.

I also wonder if you could set up magnetic protection for Mars. It's probably not that big of a feat compared to re-engineering the surface of a whole planet.

[Broomstick]

I also have some doubts about a gimmick being able to take oxygen and keep out carbon dioxide at the rates needed by human respiration being portable enough. They are two gas, and I can only think of fractional distillation methods to separate them.
But I'm nowhere near expert in rebreathers.

Let me introduce you to the oxygen concentrator which extracts oxygen from the ambient air without use of distillation techniques. Output ranges ranges from 1 liter per minute to 10. The greater the output usually the greater the size and power requirements.

Whether a sufficiently light, portable, productive, and energy efficient model could be developed for Mars is an interesting question.

[Broomstick]

And then there's the matter of pressure. With just a bit above a third of Earth's gravity, Mars would barely provide a "breathable" atmosphere even if it had all the necessary gasses in proportion. We could probably have humans adapt though, but I'm not sure how different a sea level pressure it'd end up being. I think we'd be much better off just thinking up good ways to make large colony structures. Maybe even out of clear materials, to see the sky and landscape and whatnot.

There's not a definite relationship between gravity and air density. You certainly could raise Mars atmosphere to the level of Earth sea-level pressure, you just need a HUGE amount of gas to pile onto the planet, that's all.

In this thread we had a prior discussion of human limits and the consensus seemed to be that with an Earth mix of gasses 7-8 psi or .5 bar is compatible with long-term human survival, or about half of what is normal pressure at sea level on Earth. Using Tibetans as colonists might be advantageous as they have adapted to high altitude in biological ways other people haven't. If you're adding the atmosphere to Mars you can also increase the oxygen content up to a point, which allows for a slightly lower overall air pressure, but more than about 25-30% and fires become too great a hazard.

Even if a Mars atmosphere isn't breathable, just having sufficient pressure that one could walk around in a non-pressurized suit while wearing a mask and carrying an air tank would be an improvement over a near vacuum that exists today.

[Broomstick]

The lack of magnetic field will mean even the shittiest space radiation will reach surface though.

Not necessarily. There would be more radiation than on Earth's surface, but a much thicker atmosphere would offer some protection as well.

The problem is solar flares and coronal ejection events - I'm not sure but they might blast the surface with enough radiation to be dangerous. In which case you'd need to build solar storm shelters of some sort. Basically, cellars and basements.

I also wonder if you could set up magnetic protection for Mars. It's probably not that big of a feat compared to re-engineering the surface of a whole planet.

The Earth's magnetic field is believed to be a result of the rotation of the partly molten core of the Earth. If Mars is solid all the way through good luck with that - you'd have to melt the core of the planet then get it rotating. Yeah, that's a big feat. The alternative would be some other means of generating a big ass magnetic field, which I can only assume would consume massive amounts of energy just on sheer size alone.

[Rabid]

Simple question, I hope it's not out of topic. But...

What seems to be the most cost effective solution in the longer run :

- Adapt a whole planet to human needs by using some technology very near from magitech we could only dream about today (atmospheric change, soil adaptation, etc.).
or
- Adapt humans to live in harsh condition using science, technology and biology (bio-domes, subterranean habitats, genetic engineering, etc.)


For the first solution, you need to throw some comets on Mars, hoping it to release a sufficient amount of useful gases in the Martian armosphere ; and complete the mix with Titan atmosphere for nitrogen. That suppose a very good space industry, and it'll be long before Mars could be considered terraformed.

For the second solution, it will be practical as soon as we'll have sufficiently progressed in the field of genetic engineering, and maybe nanotechnology.


What's your opinion ?

---

Yeah, 30% of an atmosphere is already far better than 0.3%. Question is : Where do you get all that nitrogen / neutral gas ?

I vote for comets.

---

The problem is solar flares and coronal ejection events - I'm not sure but they might blast the surface with enough radiation to be dangerous. In which case you'd need to build solar storm shelters of some sort. Basically, cellars and basements.

That is not a concern if you already build underground (as it will probably be the case for the 200-400 first years of Martian Colonization anyway)

[Broomstick]

What's your opinion ?

Do both?

The problem is solar flares and coronal ejection events - I'm not sure but they might blast the surface with enough radiation to be dangerous. In which case you'd need to build solar storm shelters of some sort. Basically, cellars and basements.

That is not a concern if you already build underground (as it will probably be the case for the 200-400 first years of Martian Colonization anyway)[/quote]
The thing is, people will have some need to move around at and above the surface. Perhaps there will be shelters alongside roads in rest stops. Or perhaps vehicles intended for distance travel will have some sort of shelter incorporated into them.

[Simon_Jester]

One obvious thing for shelter to do is just pile sandbags on the roof of the vehicle or something when a high-radiation event occurs, or dig a shelter and use the vehicle itself as cover over the top. But that would take time. I'm not sure how much advance warning you get of major solar activity.

Generating a magnetic field for Mars is, in all probability, out of the question.

[darthdavid]

I've heard talk of using superconducting wire to create a magnetic field for a mag-sail. Could something similar be scaled up large enough to create a planetary magnetic field?

[eion]

I've heard talk of using superconducting wire to create a magnetic field for a mag-sail. Could something similar be scaled up large enough to create a planetary magnetic field?

The problem with that is that unless the superconducting wire is functional at near room temperature, you're going to expend a lot of energy keeping it cold. In space this is far less of a problem due to the lack of conductive and convective heat tranfer.

You're honestly better off just piling dirt on top of your buildings. It'll cut down on your heating bills as well, but honestly the ammount of radiation you get once you've got a breathable atmosphere over your head is rather low.

[someone_else]

There's a variety of inert, heavy gases that you could probably use

Can you list some of your favourites anyway?

Let me introduce you to the oxygen concentrator which extracts oxygen from the ambient air without use of distillation techniques.

Uhm. It uses "sponge" materials that remove nitrogen from the air. Swap those with a carbon-dioxide "sponge" and you are set.
Good.

What seems to be the most cost effective solution in the longer run :

It is nearly OT. But I'm feeling good.
What is the most cost-effective solution you ask? Orbital stations, of course.
You want to generate a mag-field to protect you? You can since a station is vastly smaller than a planet.
You want Earth gravity? you can spin it.
You want breathable atmosphere? you can have whatever atmosphere you like.
Techlevel needed? Ours is more than enough.

Terraforming has always been an overly expensive enterprise to get something that isn't really interesting anyway.
Genetic engineering on humans isn't anywhere close to being easier, trust me.

Question is : Where do you get all that nitrogen / neutral gas ?
I vote for comets.

I doubt there are enough comets for that, Titan is FAR, just as Saturn's rings (the best source for ices of manageable size in solar system).
I vote to shut up Zubrin and set up a moon refuelling station with lunar elevators plus a few of these as orbital tugs. Just for kicks.

Although may help an eventual exploitation of lunar or NEO resources to build orbital habitats.

I'm not sure how much advance warning you get of major solar activity.

There is NOAA's space weather prediction center.
And failing that, you have around two hours between the flare detection and its arrival on Earth (on Mars it will take a little more since it is a little farther), since the harmful radiation is particle radiation, going far slower than the light show that a flare puts up.
Although a flare on January 20, 2005 took only 15 minutes to reach Earth (particles travelling at 1/3 lightspeed), so something may still catch you off-guard.

I've heard talk of using superconducting wire to create a magnetic field for a mag-sail. Could something similar be scaled up large enough to create a planetary magnetic field?

Sure. But that's a mindboggling quantity of power you are throwing away, even ignoring the inefficiencies eion pointed out.
Mars may look small on size comparisons but is still pretty damn HUGE for anything you care to do on it.

[Rabid]

Terraforming has always been an overly expensive enterprise to get something that isn't really interesting anyway.

My point. If we have the technology to travel in space, we are better off staying in space, in my opinion. Or at least hidden in some rocks in the Main Belt... If we wish to exploit the natural resources of a planet, just send'em the 'Bots to do the job, with only little colonies to maintain them. After all, we'll all have robots in the future, anyway ? No ? No?...

Oh crap...

Question is : Where do you get all that nitrogen / neutral gas ?
I vote for comets.

I doubt there are enough comets for that, Titan is FAR, just as Saturn's rings (the best source for ices of manageable size in solar system)

Launch a hundred or thousand of automated asteroid-tug into the the Oort Cloud, wait 200-500 years, and you'll finally get enough comets to set the beginning of an atmosphere. As for Titan, I recognize it will be hard to transport so much nitrogen... Maybe the spatial equivalent of a fleet of LNG ships ?
About Saturn's rings... I think if you do that, you'll have to put a hell of a fight against Space Greenpeace.

---

What's your opinion ?

Do both?

Yes, that's the safest bet.

[Lord of the Abyss]

What seems to be the most cost effective solution in the longer run :

- Adapt a whole planet to human needs by using some technology very near from magitech we could only dream about today (atmospheric change, soil adaptation, etc.).
or
- Adapt humans to live in harsh condition using science, technology and biology (bio-domes, subterranean habitats, genetic engineering, etc.)


For the first solution, you need to throw some comets on Mars, hoping it to release a sufficient amount of useful gases in the Martian armosphere ; and complete the mix with Titan atmosphere for nitrogen. That suppose a very good space industry, and it'll be long before Mars could be considered terraformed.

For the second solution, it will be practical as soon as we'll have sufficiently progressed in the field of genetic engineering, and maybe nanotechnology.


What's your opinion ?

Terraforming would probably be necessary for the genetic engineering solution to work well. Adapting humans to a thicker, warmer high carbon dioxide atmosphere is going to be much easier and less drastic than making them not need oxygen at all (and all the other problems present Mars has). If Mars is brought to the point that a breathing mask will do, then installing the biological version probably won't be too hard.

I've heard talk of using superconducting wire to create a magnetic field for a mag-sail. Could something similar be scaled up large enough to create a planetary magnetic field?

Sure. But that's a mindboggling quantity of power you are throwing away, even ignoring the inefficiencies eion pointed out.
Mars may look small on size comparisons but is still pretty damn HUGE for anything you care to do on it.

Such a superconducting ring or rings wouldn't use any power once the initial current was set up; the current will last indefinitely. So you may be overestimating how much it would take. And they could likely be charged up over time by solar power; if the goal is to keep the atmosphere from being blown away it doesn't matter if it takes a decade or even a century given how long it would take the solar wind to strip a terraformed atmosphere. A thicker atmosphere alone will shield the creatures on the surface adequately, especially with a little genetic engineering for greater radiation resistance. After all, life on Earth survives magnetic field reversals, where its own field goes to zero for a time.

[Simon_Jester]

What seems to be the most cost effective solution in the longer run :

It is nearly OT. But I'm feeling good.
What is the most cost-effective solution you ask? Orbital stations, of course.
You want to generate a mag-field to protect you? You can since a station is vastly smaller than a planet.
You want Earth gravity? you can spin it.
You want breathable atmosphere? you can have whatever atmosphere you like.
Techlevel needed? Ours is more than enough.

The problem I have with orbitals isn't physical, it's social. Orbitals require tight social controls to function, as well as tight physical controls. A terraformed planet at least theoretically offers the option of being able to move away from aspects of the local society you don't like on a small budget. An orbital doesn't, unless space travel is made very, very cheap. And even then... where would you move to, if everyone lives in orbitals?

To quote Charles Stross:

"After about forty years of bloodshed and the eventual suppression of the last libertarian fanatics, the Septagon orbitals gravitated toward the most open form of civilization possible in the hostile environment of an asteroid belt. This meant intensive schooling, conscript service in the environmental maintenance crews, and zero tolerance for anyone who thought that hanging separately was better than hanging together."

And I'm not at all sure he's wrong. Granted it's understandable, but I'm worried that people who consider this a superior way for humanity to live in space aren't really taking that side of the picture into account.

Such a superconducting ring or rings wouldn't use any power once the initial current was set up; the current will last indefinitely. So you may be overestimating how much it would take...

Trust me on this one, with superconducting magnets the fact that there's no electrical resistance is vastly offset by the need to cool the damn things. They don't run cheap, even the ones that run at liquid nitrogen temperatures (though those are at least a bit more failure tolerant).

[someone_else]

The problem I have with orbitals isn't physical, it's social. Orbitals require tight social controls to function, as well as tight physical controls.

Why? It's not like a 2 km wide rotating ring keeping in 1 atm of pressure will be made of tinfoil and duct tape.
Nor it will depressurize so fast/easily since anyone with a brain can compartimentalize it.
The same goes for life support machinery.

There will be a Quick Response team ready for both decompression and chemical hazards, some dedicated automation to shut close valves, and people will be taught what to do in those situations.

You can have the government form you like. That's just a block of flats IN SPAAACE!!! after all, and if people own their private abitative section ("house") it will tend to be handled as one on Earth.
Some further read about orbitals and governments

Maybe they won't let you buy a .50 rifle, though.

An orbital doesn't, unless space travel is made very, very cheap. And even then... where would you move to, if everyone lives in orbitals?

This assumes every orbital is ruled by Stailinist red commies, wich won't be the case.
Still, Orbitals by definition orbit something. I see no pratical reason to make them on other orbits than Earth's. So get down on the good old Earth if you don't like them. Orbital traffic is probably cheap as chips already, otherwise noone would have built those orbital colonies.
Just drop a fuel fab on the moon and you're set. Cheap fuel for all.

And I'm not at all sure he's wrong. Granted it's understandable, but I'm worried that people who consider this a superior way for humanity to live in space aren't really taking that side of the picture into account.

I never said it was superior. I said cost-effective.

But anyway, what makes the difference between the nightmarish view from that writer and reality is how much babysitting the machinery keeping you alive needs.
Even here on Earth there is a cadre of plumbers, electricians, the guys fixing power and telephone lines, the people fixing roads, and so on and so forth. Remove one of them and civilization as we know it goes to hell.

Personally, I think making a hab that doesn't need more than 25% of the population dedicated to maintenenace isn't so mindbogglingly hard.
It's not like ISS needs a lot of mainteneace today.

[Lord of the Abyss]

Such a superconducting ring or rings wouldn't use any power once the initial current was set up; the current will last indefinitely. So you may be overestimating how much it would take...

Trust me on this one, with superconducting magnets the fact that there's no electrical resistance is vastly offset by the need to cool the damn things. They don't run cheap, even the ones that run at liquid nitrogen temperatures (though those are at least a bit more failure tolerant).

Even in space, at Mars distances from the Sun? It's not like a ship; there won't be any fleshy bodies or engines* onboard to produce heat.

And I presumed we'd be using liquid nitrogen temperature or better ones.


* Presumably they could be kept in proper position by their own power - doubling as magnetic sails - or by lightsails.

[Broomstick]

The whole social angle in orbital habitats is bullshit. It comes either from repetition (a brain bug basically - probably started as a small legitimate case, then telephone gamed out of control and by now, you've heard it so many times you believe it) or misconceptions.

I come down on the side of overblown, but with a kernel of truth. If you're in an environment where the actions of one person can spell disaster or death of the group then there must be stronger social controls if the group is to survive. That doesn't mean mind control, extensive brainwashing, or keeping everyone in lockstep.

Clearly, if you're in Earth orbit anyone who dissents strongly enough can simply go back to Earth. If there are alternatives to a given orbital you can go there. But the further away from other people you are, the more isolated you are, the stronger the controls must be to insure group survival. Bad enough if someone shoots himself in the head - worse if by doing so he causes a major hull breach in a space habitat.

It's a lot harder to destroy everyone on a planet's surface than in a "habitat". That's one argument for terraforming - if you convert a planet to shirt-sleeve environment like Earth's (more or less) you can allow more crazy. However, the cost of doing so may outweigh the benefits. If you don't terraform Mars then you can have multiple large habitats on the planet for something between orbitals and a freely avaialble surface - again, it would allow for more crazy, but not as much as Earth's surface.

[Junghalli]

For the Martian atmosphere and hydrosphere, you aren't necessarily restricted to what's already on Mars. The outer solar system has plenty of ices; you could create a tailor-made atmosphere and hydrosphere if you needed or wanted to.

One possible issue is the amount of CO2 needed to create the necessary greenhouse effect. Faint sun paradox solution calculations suggest an atmosphere with thousands of times present CO2 (>10% of the present atmosphere) to keep early Earth warm with 2/3 our present sunlight (the early sun was dimmer than it is today). Here's a paper for reference. Mars recieves less than half our sunlight. It may be possible to create a warm Mars with an atmosphere rich in both oxygen and CO2, but baseline humans could not breathe such an atmosphere - CO2 is poisonous to us at such levels.

One possibility is to use a different greenhouse gas. For instance, this site lists hydrofluorocarbons as having "global warming potential: 4,000 to 10,000 times that of CO2", so even trace concentrations could create an enormous greenhouse effect. Another possible solution is to use orbiting mirrors to concentrate more sunlight onto Mars, giving it a roughly Earthlike energy balance.

What seems to be the most cost effective solution in the longer run :

- Adapt a whole planet to human needs by using some technology very near from magitech we could only dream about today (atmospheric change, soil adaptation, etc.).
or
- Adapt humans to live in harsh condition using science, technology and biology (bio-domes, subterranean habitats, genetic engineering, etc.)

Colonizing Mars with enclosed artificial habitats would probably be a lot easier than terraforming. It's a simple question of scale. Creating an enclosed habitat requires creating and sustaining an artificial environment on a relatively small scale, and repeating the process over however many habitats. Terraforming essentially means doing the same thing, only on a scale many orders of magnitude larger, and probably with much less precise control (it'd probably be a lot harder to adjust the climate, air etc. over a planet than in a small habitat). In terms of the amount of environment that must be re-engineered, enclosed habitats are much more efficient, and present much less problem of scale. This is, of course, a naive analysis (the two challenges are really very different in detail), but I think the essential comparison can still be made.

Actually adapting a human to survive on the surface of Mars as it is today without protection ... that would be very difficult. IIRC water won't even stay liquid on Mars because of the low pressure - your Martian would have to be covered with some kind of biological pressure suit, or (probably even harder) you'd have to somehow engineer a physiology that could function without water, at which point you're basically redesigning life from scratch.

The problem I have with orbitals isn't physical, it's social. Orbitals require tight social controls to function, as well as tight physical controls. A terraformed planet at least theoretically offers the option of being able to move away from aspects of the local society you don't like on a small budget. An orbital doesn't, unless space travel is made very, very cheap.

On another board I remember Destructionator mentioning that travel within a close cluster of habitats might not be very difficult at all; your spacecraft could just be an airtight box that's launched by the habitat's own rotation and drifts over until it's snagged by another one (I forget all the specifics). At any rate, even rockets could probably be a lot cheaper between habitats than surface to orbit. Getting between habitats in similar orbits probably wouldn't take much delta V, so no need for staging, and no need to worry about having enough thrust to fight gravity, or the stresses of atmospheric re-entry ... a strictly habitat to habitat ship would be a lot easier to build than a surface-orbit-surface ship.

[Simon_Jester]

Even in space, at Mars distances from the Sun? It's not like a ship; there won't be any fleshy bodies or engines* onboard to produce heat.

It'll be in direct sunlight, soaking up something on the order of 500 to 600 watts per square meter, much of the time.

You can maintain cryogenics in space, naturally; chemical rockets do so routinely. But it's not trivial and it does require ongoing consumption of power. Also a certain amount of structural strength: if you place magnetic coils in vacuum and use them to exert magnetic force on the solar wind, they will feel forces in the opposite direction pushing them around. You need mechanical strength and station-keeping thrusters to hold them in place.

It might be a viable solution for all I know; I've never heard it proposed before and I don't know what to think about it.

* Presumably they could be kept in proper position by their own power - doubling as magnetic sails - or by lightsails.

That won't work well, because to do their job they must push the solar wind away from the planet. That inevitably pushes them away from where you want them.

[Rabid]

So, if I may summarize...

You can get a Mars with an atmosphere of 100-300 hectopascals (0.1-0.3 bar), composed mostly of oxygen and nitrogen (or any gas that fit the same role as nitrogen), with important traces of CFC to have an average temperature of -20 /-10 °C (-4 / 14 °F).
That leaves us a thin but breathable atmosphere in which a human could survive without horrible difficulties, with a bit of technology (breather mask and a good parka) or with a shit-tonne of genetic engineering if you feel like it.

To obtain this atmosphere, you can dump some comets on the planet, melt the ice caps, throw in some genetically engineered bacteria / nanorobots to turn the various ice-stuff and rock-stuff into useful stuff, and mine the various fluorite of the Martian environment to mass-produce CFC (you won't get an Ozone Layer with that, I think...).

So there you have a planet with an atmosphere, but now you have to engineer a complete biosphere, or else in a millenia or ten all the Oxygen will be fixed back on the Martian rocks (ferro-oxidization AKA rust) and you'll have to do it all again.
And you'll hit a wall at first while trying to create a biosphere when you'll realize that Mars soil is highly toxic to terrestrial usual lifeforms, so you'll have to treat Mars soils before being able to, say, plant trees or crops, even reasonably genetically engineered.

Do I miss something ?

[Broomstick]

I come down on the side of overblown, but with a kernel of truth. If you're in an environment where the actions of one person can spell disaster or death of the group then there must be stronger social controls if the group is to survive.

Yeah, but unless that one person has a nuclear bomb, he can't really spell disaster for the whole group.

It depends on how big the habitat is, doesn't it? The smaller the habitat the more fragile it is.

Bad enough if someone shoots himself in the head - worse if by doing so he causes a major hull breach in a space habitat.

That's horribly unrealistic.

OK, so I exaggerated a bit. How about someone making a crude pipe bomb and blowing themselves up, breaching the hull, causing environmental problems, etc.

Someone going wild and free with big military weapons, tanks, missiles, battleships, shit like that could make trouble happen really fast. But if you pass a law prohibiting private ownership of operational battleship guns, I don't think it would affect very many people's lives!

Yeah, sort of the point - you don't need draconian controls to maintain reasonable safety in a large habitat.

Most the environmental regulations, for regular people, would probably be similar to what we have today. Don't start forest fires, don't burn toxic shit in your back yard, don't litter, that kind of thing.

It would have to be either stricter, better enforced, or both. A space habitat is a small, closed system, there's less room to dilute and mitigate environmental contamination and negative effects.

One thing did just come to my mind though: what if you turned on a hose in your yard, and left it there? If water pooled around the inner hull, that might be a problem. (though there's feet of earth between you and there, so it shouldn't be a big deal most the time). Perhaps the hab will include underground ditches to catch and reclaim it in these scenarios. Though this is a potential thing to regulate too. The easiest way seems to me to be to just charge for water like we do today, to discourage excess use. Problem solved, at least in likely practical terms.

There are, occasionally, people in the real world who more or less do that - turn on the backyard hose and leave it going, damn the cost, and it can have serious consequences for neighbors due to flooding, damage to building foundations, etc. Of course, we have courts, community, and police who can step in and force the water to stop - and I would imagine that any space habitat would have the same. The same controls we have on a planet. In other words, no more or less extreme than what we currently have.

[someone_else]

It depends on how big the habitat is, doesn't it? The smaller the habitat the more fragile it is.

Too small habitats are unpratical on purely mechanical reasons.
It must be big enough to avoid the need to balance it when people move around while it is spinning (and it will spin for a long time of its service life).
Otherwise you need to place ballasts and stuff to compensate and it's a pain.
Anything massive enough to avoid that problem has a population close to a thousand at least.

It would have to be either stricter, better enforced, or both. A space habitat is a small, closed system, there's less room to dilute and mitigate environmental contamination and negative effects.

A space habitat is a compartimentalized system. Forget all those "open space" cylinders where people live on ground-like areas and private homes mimicking US suburbs.
Overly inefficient disposition. That will be the "pubblic park" area at best. Maybe with some farms.
The people will inhabit apartments and flats in its "underground" levels. Which if you think about it, isn't terribly different from New York anyway.

This more than likely means that the section where the moron is burning shit will be immediately sealed shut and powerful vents that were used to move normal air through the "air conditioning" will move toxic fumes away. We can do it with tunnels and chemical labs, we can do it in space too.
And obviously, since the area has been shut closed, finding the moron is easy.

Also, there will be much more peer pressure, but that's true of any shared-ownership structure anyway.

How about someone making a crude pipe bomb and blowing themselves up, breaching the hull, causing environmental problems, etc.

Is that different from a kamikaze here on Earth?
Since the sections can be sealed, the damage dealt is limited. And if they don't guard a few sensitive areas like life support machinery, they deserve it imho.

If water pooled around the inner hull, that might be a problem. Perhaps the hab will include underground ditches to catch and reclaim it in these scenarios.

Any place where you have plants must have a decent draining system, otherwise roots rot away. Wondering why most pots have a hole in the bottom?

So, if I may summarize...

More or less... and in the same time with the same expenditure you can probably set up a dyson sphere. Not the shell kind, the "swarm of orbiting stations" kind.

The outer solar system has plenty of ices; you could create a tailor-made atmosphere and hydrosphere if you needed or wanted to.

Yes, if you can shovel hundreds of trillions of tons of ices from planets located 20+ AUs from here. (Oort cloud is much farther than that)
Btw, has anyone an idea of the weight of a human-breathable atmosphere on Mars?
I did some overly eyeballed calcs in the past, but... yeah.

One possibility is to use a different greenhouse gas.

Interesting. So, civilizations that have such capability can use CFC or similar instead of unbreathable levels of CO2.
I totally forgot about such chemicals!

Colonizing Mars with enclosed artificial habitats would probably be a lot easier than terraforming.

But much worse than building an orbital station and sharing the same drawbacks.

your Martian would have to be covered with some kind of biological pressure suit

Human skin is enough. Look for the mechanical pressure suits. It's drinking and eating that will be a major problem.

At any rate, even rockets could probably be a lot cheaper between habitats than surface to orbit.

Are you kidding me right? They ARE a lot cheaper , since they require at best 4-5 km/s of delta-v, while liftoff from Earth is well above 10 km/s of delta-v.
Chemical rockets feel at home with such performance requirements. NERVAs are overkill.