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Some thoughts and ideas for terraforming Mars.

First, 5 satellites with gigantic Hubble size magnifying glass (made from spaceage plastic infused quartz) and a parabolic mirrors. And some on the ground to melt the ice caps and to heat it up and get oxygen and hydrogen released into the environment. Next, seed the planet with genetically modified corn...That will produce without the need for polonization...For the photosynthesis, air purifiers, also microbe and parasitic collectors Wait about 5-10 years while environmental texts are going on. Once you have enough water...ditch the magnifying glasses (use them to make another hubble), but keep the mirrors to give light and warmth around the planet at night.

Just thought I would share what I have been upto in my HU game.

You've got a couple of problems off the bat with this. Melting the ice-caps is one thing, but I'm not sure it's going to be all that easy to crack the water molecules to get free oxygen and hydrogen. There's also the issue of that much hydrogen not being good to have floating around either. But most of the stuff I've seen mentions needing a lot more Ice/Water to crack to give Mars a breathable atmosphere and the fact that what happened in the past will still happen as that atmosphere is going to be stripped from the planet by the solar winds due to it's general lack of a global magnetic field.


Daniel Stoker

Daniel Stoker wrote:You've got a couple of problems off the bat with this. Melting the ice-caps is one thing, but I'm not sure it's going to be all that easy to crack the water molecules to get free oxygen and hydrogen. There's also the issue of that much hydrogen not being good to have floating around either. But most of the stuff I've seen mentions needing a lot more Ice/Water to crack to give Mars a breathable atmosphere and the fact that what happened in the past will still happen as that atmosphere is going to be stripped from the planet by the solar winds due to it's general lack of a global magnetic field.


Daniel Stoker

Oh, I fixed that already. Mars now (or in this case, once again) has a semi stable and workable magnetic field. The 5 sided pyramid turned out to be a generator, it's repaired. Did you actually think that I would do this other wise?

How did you crack all the water and what are you doing with that atmosphere that rich in hydrogen? And are you sending ice-comets in to get more water/ice on the planet?


Daniel Stoker

We used to have a poster here named Phalanx who was a legit rocket scientist. His approach suggested using captured icy meteors with rockets to glance off of Mars' atmosphere to thicken up said atmosphere. I think he has some ideas for the magnetic problem as well, but I don't recall what they were or if I'm remembering wrong.

Daniel Stoker wrote:How did you crack all the water and what are you doing with that atmosphere that rich in hydrogen? And are you sending ice-comets in to get more water/ice on the planet?


Daniel Stoker

Lasers, from space, hints the huge magnifying glasses. Burnt it off. I will be before the 1st year is up, so, that is in future. For the record, I'm also mining the asteroid belt. But, right now, I'm using what I have to work with...And no, it's not all over the planet yet.

The Artist Formerly wrote:We used to have a poster here named Phalanx who was a legit rocket scientist. His approach suggested using captured icy meteors with rockets to glance off of Mars' atmosphere to thicken up said atmosphere. I think he has some ideas for the magnetic problem as well, but I don't recall what they were or if I'm remembering wrong.

Cool.

The thing to do is to get a few (100 or so) comets to replenish the atmosphere as the 1st steps of T-Forming Mars.
Got to have an atmo before you do much else.

Yeah...It's on the to do list. The hard thing was waiting to see if the planets core would reboot after I fixed the magnetic field generator. I am not a patient man...But we managed.

pblackcrow wrote:Some thoughts and ideas for terraforming Mars.

First, 5 satellites with gigantic Hubble size magnifying glass (made from spaceage plastic infused quartz) and a parabolic mirrors. And some on the ground to melt the ice caps and to heat it up and get oxygen and hydrogen released into the environment. Next, seed the planet with genetically modified corn...That will produce without the need for polonization...For the photosynthesis, air purifiers, also microbe and parasitic collectors Wait about 5-10 years while environmental texts are going on. Once you have enough water...ditch the magnifying glasses (use them to make another hubble), but keep the mirrors to give light and warmth around the planet at night.

Just thought I would share what I have been upto in my HU game.

For 5 satellites, you are going to need a bigger lens than one on the Hubble. You don't even need a magnifying glass, just mirrors actually. I see what you intended, but I don't recall reading about such a suggestion to teraform, so it might not be as practical in actual use.

It might be easier to put "soot" on the ice to have it melt quicker. I don't think you need to breakdown the water into O2 and H2, you can get the O2 from the CO2 in the atmosphere from the plants and likely "mining" the atmosphere for materials (Robert Zubrin's Mars Direct Proposal would use H2 to mine CO2 from the atmosphere to make methane and O2).

Can't comment on the GE Corn to remove the need for pollination.

Still 5-10years would be overly optimistic I think, you are likely looking at a century or more.

You don't need the mirrors to warm Mars if you have enough CO2 in the atmosphere.

A very interesting suggestion I have heard is moving CO2 from Venus' Atmosphere(which has too much CO2) to Mars. The best part is, with CO2, a small amount of oxygen and Water, you have the basic needs of plant life. They can then oxygenate the atmosphere.

One of the other issues is that Mars has an insufficient magnetic field. That means that you'll either need to make one, or a sufficiently thick atmosphere to block most harmful radiation. Also, a magnetic field will prevent the sun from stripping the atmosphere away over the course of millions of years.

This is all a herculean task that will take decades to centuries, but it seems like the most plausible way.

The Artist Formerly wrote:We used to have a poster here named Phalanx who was a legit rocket scientist. His approach suggested using captured icy meteors with rockets to glance off of Mars' atmosphere to thicken up said atmosphere. I think he has some ideas for the magnetic problem as well, but I don't recall what they were or if I'm remembering wrong.

Making a magnetic field for Mars will be pretty tricky. You could find a way to re-liquefy the core of the planet and let the fluid dynamics of it generate a magnetic field. The most plausible way to generate a field artificially would be a massive rapidly rotating ring of ferrous material in orbit around the planet. Very tough to accomplish, but workable.

Edit: You know, as I think about it some more, that ring doesn't necessarily have to be in orbit. It should also work on the ground. Build a rail line circumnavigating the planet at the Equator and maybe a few other lines of latitude north and south of it. Then have numerous Iron-rich payloads traveling at high speed around the planet. Get enough of em, and boom! Artificial magnetic field!

Just use a fancy* drill to get to the core and then summon some earth or fire elemental intelligences to restart it(a new home for them).
Use a series of low broad domes(think plastic/greenhouses instead of giant glass things) to keep in new atmosphere you summon with air elemental magic. Maybe have a couple "rings" of these in the area below the poles you are melting with lichen.
Having recently watched The Martian, you might want to talk to a farmer about "fertiliser" so you can grow some crops and thus claim to have "colonised" mars.




*lasers, nanobots, magic, technomagic, antimatter, whatever....

this is really cool. great post as always Shannon.

ShadowHawk wrote:this is really cool. great post as always Shannon.

One of the actual ideas nasa had was landing huge smoke stack like structures on mars and pumping out loads of CO2 into the air.

Building an atmosphere of pollution would be something humanity would excelle at.

VR Dragon wrote:One of the actual ideas nasa had was landing huge smoke stack like structures on mars and pumping out loads of CO2 into the air.

Building an atmosphere of pollution would be something humanity would excelle at.

Except it would be prohibitively expensive to ship the pollutants from Earth to Mars, you'd be better served finding deposits that could be converted into suitable atmospherics and that suffers the limitation of having to ship the infrastructure to make the atmosphere factories.

No because the soul of mars is red because of a lot of oxide....

Remove the CO from the very dirt of the planet.....

Just have to send the very messy smoke stacks.

There are also other greenhouse gases that could be vented into the atmosphere that are more effective that plain CO2.

Unless you can restart or create a new electromagnetic field strong enough to shield the planet from the solar winds then no matter how you create the atmosphere it will be blown away by the sun itself...

Slight001 wrote:Unless you can restart or create a new electromagnetic field strong enough to shield the planet from the solar winds then no matter how you create the atmosphere it will be blown away by the sun itself...

Except that kind of thing would take millions of years minimum, good odds either your species goes extinct before that matters or evolves to the point it can maintain the atmosphere indefinitely.

Nightmask wrote:

Slight001 wrote:Unless you can restart or create a new electromagnetic field strong enough to shield the planet from the solar winds then no matter how you create the atmosphere it will be blown away by the sun itself...

Except that kind of thing would take millions of years minimum, good odds either your species goes extinct before that matters or evolves to the point it can maintain the atmosphere indefinitely.

I've already covered this using elementals to do it in your lifetime.

Sir_Spirit wrote:

Nightmask wrote:

Slight001 wrote:Unless you can restart or create a new electromagnetic field strong enough to shield the planet from the solar winds then no matter how you create the atmosphere it will be blown away by the sun itself...

Except that kind of thing would take millions of years minimum, good odds either your species goes extinct before that matters or evolves to the point it can maintain the atmosphere indefinitely.

I've already covered this using elementals to do it in your lifetime.

Creating or maintaining? Because creating would be infinitely more difficult than maintaining and even maintaining would require a LOT of elementals and by extension you'd have a LOT of VERY unhappy elementals being trapped as nothing more than atmospheric generators.

With regards to the solar wind, it'd also be far weaker at that distance than it is where we are so isn't going to ablate the atmosphere anywhere near as quickly as it would (and does) here. Not that it would hurt to set up some kind of protective shield or barrier to help block it from the planet, it'd be far cheaper having an array of solar sail satellites intercepting the solar wind than trying to get the planet's magnetic field going again, plus depending on you tech level you could have them be power satellites feeding power to the planet at a minimum you'd be able to convert the diffuse energy they capture into a more concentrated level to heat and light the planet better than it currently is (since the farther you have to place the satellites the wider the area they have to block to contain the solar wind and the more sunlight they can absorb and divert).

No, volcanoes and planetary cores can have elementals who are happy where they are.
There are some in Mt.Nimro for instance.
As long as you leave them be and aren't poking them or whatever, they can be happy. Keep in mind that for all the "elementals are unhappy here" talk they are also said to be occasionally curios and in the pfrpg Dragon's and God's book we get mention of them being curous about our world. And rules for elemental possession. So, there is wiggle room, if you want.

Sir_Spirit wrote:No, volcanoes and planetary cores can have elementals who are happy where they are.
There are some in Mt.Nimro for instance.
As long as you leave them be and aren't poking them or whatever, they can be happy. Keep in mind that for all the "elementals are unhappy here" talk they are also said to be occasionally curios and in the pfrpg Dragon's and God's book we get mention of them being curous about our world. And rules for elemental possession. So, there is wiggle room, if you want.

Still you're talking about easily thousands if not more elementals to make such a thing work (easily hundreds of thousands if you're trying to use elementals to introduce enough energy to reliquify the core and get operating in a suitable magnetic field generating fashion) it'd be REALLY stretching plausibility to think you could find so many elementals happy to hang around in the material world to reheat a planet's core or help produce an atmosphere for it. I'll grant it's not an impossibility but it's certainly not a high probability thing either.

Nightmask wrote:
Still you're talking about easily thousands er.

Meh, just contact a few elemetal lords and get them to move to a new kingdom. Most "elementals" are just intelligence fragments anyway...

Sir_Spirit wrote:

ShadowHawk wrote:this is really cool. great post as always Shannon.

the conversation and exchange of ideas is cool. or do you mean who's Shannon? if that's the case, PBlackCrow is. I game with him on the weekends, online.

True, and thanks everyone for your great suggestion. Will be starting year 2 planning soon.

By the way, has anyone heard of the star system epsilon eridani, it has two asteroid belts...which, technically we do to, but it's a lot easier to access with the ion propulsion drive the ones between Mars and Jupiter instead of between Makemake and Eris. But the start system is only about roughly 10 light years away.

I have just put some ice meteors lined up in the path of mars, once we extracted the larva and minerals from the ice, mind you, and killed some space pirates and captured a few ships. Hey, there is always something going on, but I need to be more careful about letting tourist with cameras on to the outer stations, especially the ore processing stations...reporters as well. We have mages and jumpers/teleporters at nexuses/nexi trying to do dimensional teleport on to the stations E-ZZ, take stuff, using pictures and videos. Logic doesn't always apply in most of these cases. Eh, oh well.

Well...Some of the larva are alive...shocked the heck out of me when the gm told me. No clue how, other then Arctic bees going into a type of suspended animation. So, I have in great haste gated them all to the British science station, (Station G), to find out #1 what the hell they are, and #2 could they benefit the Mars Project. Waiting for the test to be concluded.

Okay, for just a moment let's be realistic about the science here:

First: Mars has an atmosphere that is only 6mbar thick. To give you a contrast compared to Earth's 1013mbar atmosphere. That's all the current magnetic field can hold.

Next: The means surface temperature of Mars is -67 degrees F. That is like Alaska in the Winter!!!! Water turns to Ice at those temperatures. So even if you slammed 100000 water Ice comets at the surface they would essentially be mountains of water ice!

Next: Mars does have an active magnetic field but much of it's interior has solidified. This is bad for Thermodynamics in general. It's Core is still cooling and it will eventually lose all of it's Atmosphere to the Solar Winds ending up like our moon, which has a 1mbar Atmosphere, so Mars is not too far off.

Now I did see one of you post about putting CO2 in Mars' atmosphere? Mars' current atmosphere is already 95% CO2. It has been that way for billions of years and the atmosphere isn't getting any thicker or warmer.

So then, the big question is how do you terraform Mars without breaking the suspension of disbelief of most educated players?

Simple, steal the idea from the movie Total Recall, go underground. It is far more feasible for a future Martian society to live within the mountains of Mars. There is an abundance of Iron on the planet, CO2 scrubbers could be set up and all you would have to import is Nitrogen gas, like Earth. Since Nitrogen is an inert gas to humans it is never consumed. Underground hydroponics could be set up for air and for food purposes and since there are no Mars quakes of any importance the geology of the planet is pretty sound.

Also consider that Mars is a micro gravity .37g (compared to Earth at 1.0g) world. Assuming that you had Starship technology, then you would have to have artificial gravity set up everywhere otherwise the Human body would weaken and could never live on a planet like Earth again.

jlm2924 wrote:Okay, for just a moment let's be realistic about the science here:

First: Mars has an atmosphere that is only 6mbar thick. To give you a contrast compared to Earth's 1013mbar atmosphere. That's all the current magnetic field can hold.

Next: The means surface temperature of Mars is -67 degrees F. That is like Alaska in the Winter!!!! Water turns to Ice at those temperatures. So even if you slammed 100000 water Ice comets at the surface they would essentially be mountains of water ice!

I think you're missing the small point that the impact is going to shatter and melt at least some of that ice releasing more moisture into the atmosphere which will help to thicken it slightly and increase heat retention and every little bit helps. Once you've got the ice there you can then work on melting it yourself for whatever's left and as things warm and the atmosphere thickens the process will slowly accelerate.

jlm2924 wrote:Next: Mars does have an active magnetic field but much of it's interior has solidified. This is bad for Thermodynamics in general. It's Core is still cooling and it will eventually lose all of it's Atmosphere to the Solar Winds ending up like our moon, which has a 1mbar Atmosphere, so Mars is not too far off.

Now I did see one of you post about putting CO2 in Mars' atmosphere? Mars' current atmosphere is already 95% CO2. It has been that way for billions of years and the atmosphere isn't getting any thicker or warmer.

Because it's already thin and there isn't much it can do with what it has, and just like a thin blanket won't keep you as warm as a thick blanket a thin amount of CO2 isn't going to retain heat as well as a thick blanket of it would so of course you would among other things need to add even more CO2 along with other gasses to help thicken the atmosphere and warm the planet.

I think I see where you are going with this. When an object enters say Earth's atmosphere, because we have such a thick atmosphere (1013mbar as I had mentioned) this does create friction and as such creates resistance and heat. So asteroid/comet/satellite/space station falls to Earth, it catches fire and "burns" in the atmosphere upon reentry. This is the basis for your 'comet melting upon re-entry theory'.

Problem: Mars' atmosphere is 6mbar thick. The object will just hit the surface with little or no friction at all. Want the proof? When we landed the Mars Rover we had minimal shielding, a parachute that was extra large for an object of it's size (like 3 of them) and airbags! So why was all that necessary? Less atmosphere means less friction and resistance upon reentry. Plus Mars is a little more than 1/3 of Earth's gravity so there is less pull on the object and the airbags simply let the rover land safely and not break.

So lets assume your space ship finds a Comet that is <mostly> pure water and it's say the size of Mount Everest. It then tractor beams it to Mars and throws it at the planet at a relative safe speed, call it Mach 1. Mars' atmosphere will slow the decent some, and yes there will be friction. This will not melt the comet but rather break smaller pieces off. So you still have a comet the size of Mt. Fuji falling to the surface at incredible speeds. *BOOM* there will be a colossal explosion and now you have hill sized and mountain sized large chunks strewn about a large area, call is a few thousand square miles. In between the debris field you will have varied small chunks laying about.

Remember the ambient temp of -67 degrees F? That means that any melting that may have occurs will cause a light dusting of hail stones and then the water stays ice. So no, a water comet will not thicken the atmosphere.

The real inherent issue is the low powered Magnetic field Mars has. As I mentioned and science has proven this, in order for any planet to support a thick atmosphere it needs a strong magnetic field to keep it from being blown away by the solar winds. Currently Mars' magnetic field can only support a 6mbar atmosphere.

So even if you borrowed the vacuum maid ship from Space Balls, then you flew to the Avatar home world of Pandora and sucked up enough atmosphere to "thicken" the one on Mars; you still have the Solar Winds, the lack of a strong Magnetic Field to hold such an atmosphere and Mars would likely lose it all to outer space anyways. How long would that take? I have no idea. Years? Centuries? A few Millennia? Who knows.

One thing to point out about Mars having a weak magnetic field and thus loosing its atmosphere.
That will take a looooong time.
Its not like the atmosphere will blow away in a week, or even in decades. Your talking something thousands or tens of thousands of years.
Which is probably going to be long enough to either refresh it, or come up with another solution (or another planet)

Also... what about using shattering charges on your ice asteroid. Break it up into a large number of pieces that are spreading out and hit all over the place.
Basically instead of shooting Mars with a cannon ball, shoot it with a shotgun.

I like it. Why not?! The overall point is that if he is going to do a campaign where the PCs are trying to assist in Terraforming Mars, then try to keep the 'science fiction' somewhat believable.

Anyone watch Star Trek Voyager? There are tons of ways they could have been home in 1 day. Example: When they found that Borg Cube that was damaged and all the adult drones were dead? The cube was being run by a handful of children. So why didn't they beam on board and steal every single Trans-Warp coil on board? Oops, did the writers forget that little detail? Well no matter it happens all the time, as long as the episode was good, right?

Same can be said for running adventures. As long as the players have fun and as long as the story is presented in a believable fashion, then the players will suspend their disbelief and accept the story.

jlm2924 wrote:I think I see where you are going with this. When an object enters say Earth's atmosphere, because we have such a thick atmosphere (1013mbar as I had mentioned) this does create friction and as such creates resistance and heat. So asteroid/comet/satellite/space station falls to Earth, it catches fire and "burns" in the atmosphere upon reentry. This is the basis for your 'comet melting upon re-entry theory'.

Problem: Mars' atmosphere is 6mbar thick. The object will just hit the surface with little or no friction at all. Want the proof? When we landed the Mars Rover we had minimal shielding, a parachute that was extra large for an object of it's size (like 3 of them) and airbags! So why was all that necessary? Less atmosphere means less friction and resistance upon reentry. Plus Mars is a little more than 1/3 of Earth's gravity so there is less pull on the object and the airbags simply let the rover land safely and not break.

So lets assume your space ship finds a Comet that is <mostly> pure water and it's say the size of Mount Everest. It then tractor beams it to Mars and throws it at the planet at a relative safe speed, call it Mach 1. Mars' atmosphere will slow the decent some, and yes there will be friction. This will not melt the comet but rather break smaller pieces off. So you still have a comet the size of Mt. Fuji falling to the surface at incredible speeds. *BOOM* there will be a colossal explosion and now you have hill sized and mountain sized large chunks strewn about a large area, call is a few thousand square miles. In between the debris field you will have varied small chunks laying about.

Remember the ambient temp of -67 degrees F? That means that any melting that may have occurs will cause a light dusting of hail stones and then the water stays ice. So no, a water comet will not thicken the atmosphere.

The real inherent issue is the low powered Magnetic field Mars has. As I mentioned and science has proven this, in order for any planet to support a thick atmosphere it needs a strong magnetic field to keep it from being blown away by the solar winds. Currently Mars' magnetic field can only support a 6mbar atmosphere.

So even if you borrowed the vacuum maid ship from Space Balls, then you flew to the Avatar home world of Pandora and sucked up enough atmosphere to "thicken" the one on Mars; you still have the Solar Winds, the lack of a strong Magnetic Field to hold such an atmosphere and Mars would likely lose it all to outer space anyways. How long would that take? I have no idea. Years? Centuries? A few Millennia? Who knows.

That actually wasn't where I was going, I specifically referenced the energy of impact melting some of it since I know there isn't enough atmosphere to effectively ablate the ice asteroid as it comes in. The kinetic energy of a megaton ball of ice impacting a planetary surface and multiples of the speed of sound on the other hand IS going to end up melting some of that and spreading it around and likely release other gases. Yes the surface in general is brutally cold but it won't prevent some water vapor existing and by making the ice available you have it on hand for a variety of uses.

As far as the weak magnetic field goes, as already noted by someone else once you do have an Earth level atmosphere it will take thousands if not tens or hundreds of thousands of years for that to fade away and you'd have to worry more about the lack of protection from charged particles the weak field provides than atmospheric loss (which given where Mars is would probably be more a result of the lower gravity than solar wind ablation). If you can manage to maintain a civilization at the appropriate level you can always replenish it whenever you need to (provided you don't create a situation where you can't just drop ice asteroids in as needed).

Sure, I can see that. But there is one final little issue. As it stands now Mars has a 95% CO2 Atmosphere. So lets say for fun you "transplant" some atmosphere from an Earth like world (I wouldn't do it from Earth) and you move some of the atmosphere to Mars (now why you wouldn't want to settle on the Earth like planet is beyond me, or maybe you opened a portal to a pocket dimension with a breathable atmosphere, either way).

At 6mbar Mars has 95% CO2.

So you increase the atmosphere to 1000mbar
+78% Nitrogen
+21% Oxygen
+01% Other (FYI, CO2 cannot exceed 0.5% or the body will start suffocating at the cellular level)

If I did the math right then the atmosphere -should- be breathable. But do remember the conditions are still freezing. Any surface water that you might transplant will still freeze solid, unless you mix it with other materials, like salt. Even then it can get quite slushy. Have a look at the Artic and Antarctic oceans. The planet is still +50% further away from the Sun than Earth is. While Earth is in the forward edge of the Goldie Locks Zone, Mars is (debatably) at the far leading edge of the Goldie Locks zone around our sun. So warming the planet is a major issue.

Like I had originally said, living underground is the best option for Mars. Even IF you managed to thicken the Atmosphere and make is safe for Humans and then you managed to bio-engineer plants, animals, and other factors to create a micro eco system you still have dangerous levels of Ultra Violet Rays from the Sun. So you would be indoors or underground all the time anyways. Night time would reach over -100 degrees F (at those temperatures flesh freezes instantly and painfully) so farming on the surface at night would be a death trap.

Just leave the atmosphere on Mars be, set your base up in the mountains or on the surface and go from there. That's the best option for you. Oh and one last thing to point out. Billions of years ago Mars did have a liquid ocean. It was a brine ocean and when it's atmosphere began to disappear so did the ocean. But where did it go is a hot debate amongst scientists. One interesting theory is that much of it could have "drained" into the porous rock and there may be vast amounts of water deep underground. Underground the water could remain a liquid, or it can even be a layer of permafrost just several feet below the surface (like Alaska). That water could be melted, purified and used to make Atmosphere in your bases, cool the reactors, and provide drinking water for the residents.

jlm2924 wrote:Okay, for just a moment let's be realistic about the science here:

Why? So you can ignore how we've already covered liquifying Mar's core? The whole point of that is to help enhance it's magnetosphere and make thickening the atmosphere easier.
We've also got suggestions for domes to hold in some of the atmosphere in the beginning.
I am not poo-pooing suggestions you've made, just pointing out that going on about things others have addressed as though no one has is a bit of a waste.

I remember one book, many years back, The Greening of Mars by James Lovelock, that had his terraforming group creating a greenhouse effect for Mars with chloro- fluorocarbons (CFCs) packed into old SLBMs bound together into booster-clusters that supposedly manage to break atmosphere and make transorbital insertion, and then on to bombard mars.....the whole stack-up struck me as rather ridiculous, in an attempt tp pull terraforming on the cheap.

Thought I'd chime in again on the "liquefying the core" idea. Game science, do what you want. Real science, the issue is not necessarily reheating the core and liquefying it. The issue is to get what's there to spin faster and make a larger magnetic field. That's the real problem. Once you have it spinning fast enough and lets say you move enough atmosphere to thin out the CO2 to human tolerance as well as put other gases we need, 78% Nitrogen and 21% oxygen, 1% other.

The other major issue is establishing an eco system that will keep the planet alive. Perhaps some bio-engineered algae? Another issue I read about that space station currently have is that humans infect the environment they live. At any given time there are over 10,000 species of micro-organisms living on or inside you. On a station they have bio-filters to deal with this, and on Mother Earth
there's the salt in the ocean that deals with this. Mars lacking the ability to maintain liquid water on the surface this could be a major problem.

A domed city or under ground colony is the best answer.