Terraforming

[Technocrat]

I think both Mars and Venus could be terraformed.

I always imagined that the best way to do this would be with directed asteroid impacts. Nuclear-powered spaceships (http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29)would be capable of delivering a large enough payload to redirect the course of asteroid. I heard somewhere that this was the reason why nuclear propulsion for spacecraft was banned as part of the nuclear test ban treaty - they were afraid the Russians were going to hit the U.S. with an asteroid :).

To terraform Venus, you would first bombard the atmosphere with smaller asteroids. They would need to be small enough to burn up in the atmosphere so that the gases are ejected into space. After a significant amount of the atmosphere has been removed you would create an ocean with ice asteroids, possibly by breaking up the dwarf planet Ceres. Due to the topography of Venus, an ocean which covered 80% of the surface would still only account for 10% of the water on earth, having an average depth of less than 100m. Finally, you would need to create an Earth-like rotation, which could be done with flybys of massive objects (60 miles or more in diameter) - this would probably be the most difficult part.

Mars would be easier. To add heat and greenhouse gasses, asteroids could be specifically chosen for their composition. Many objects in the outer solar system contain ammonia which could be used as both a greenhouse gas and a buffer gas for the Martian atmosphere (because ammonia contains nitrogen). The impact of the asteroid (they would need to be large enough to impact on the ground) would create heat and the released ammonia would act as a greenhouse gas and a buffer gas. To add water, bombard with ice asteroids.

What are people's thoughts on this?

[TheSultan]

While this sounds very interesting I think there are far too many variables involved, not to mention how many billions, probably trillions+ dollars this would cost.

[mikelepore]

To terraform Venus, you would first bombard the atmosphere with smaller asteroids. They would need to be small enough to burn up in the atmosphere so that the gases are ejected into space.

Why do you think that asteroids "burning up" (vaporized) in the atmosphere would cause gases to be ejected into space? I think it would make the atmosphere more dense.

[Q]

This sounds like a project that could take many thousands if not millions of years. Are there not more direct methods to terraform Venus?

[Revy]

I think Mars is the best option. I don't think it would need to take thousands of years. It's actually a lot more simple than you would think. You could use plants to generate oxygen because they consume carbon dioxide. although you would first need to warm up the planet and many people have suggested releasing greenhouse gases into the Martian atmosphere.

[Q]

I think Mars is the best option. I don't think it would need to take thousands of years. It's actually a lot more simple than you would think. You could use plants to generate oxygen because they consume carbon dioxide. although you would first need to warm up the planet and many people have suggested releasing greenhouse gases into the Martian atmosphere.

Well yeah, Mars. It would still take centuries though to heat up and create a dense enough atmoshere to have plants.

Venus however is quite a different story I think. You have a very dense atmosphere, a temperature of up to 450 degrees Celsius and huge vulcanic activity. The fact that Venus also has a "day" which takes longer than a Venus-year also means permanent huge storms as warmer air travels to the colder parts of the planet. And Venus has no large moon, like we do, which acts as a gravitational pull to stabilise our planet which in turns helps in having a stable climate. These are all issues which we have to tackle with terraforming.

[Technocrat]

Why do you think that asteroids "burning up" (vaporized) in the atmosphere would cause gases to be ejected into space? I think it would make the atmosphere more dense.

Isn't this what happens when an asteroid vaporizes in the atmosphere? I read somewhere that objects 100m across could eject gas from the atmosphere into space. Obviously, a great many of these would be needed, but it's not like there's a shortage of rocks in the solar system.

[Technocrat]

This sounds like a project that could take many thousands if not millions of years. Are there not more direct methods to terraform Venus?

Actually it could take decades or centuries using the methods I described. It would just require a lot of energy.

[Technocrat]

I think Mars is the best option. I don't think it would need to take thousands of years. It's actually a lot more simple than you would think. You could use plants to generate oxygen because they consume carbon dioxide. although you would first need to warm up the planet and many people have suggested releasing greenhouse gases into the Martian atmosphere.

I suggest striking mars with ammonia-containing asteroids to both heat it up, add greenhouse gasses, and add a buffer gas (nitrogen). After the planet is warmed up, plants could be planted to produce oxygen.

[Technocrat]

Well yeah, Mars. It would still take centuries though to heat up and create a dense enough atmoshere to have plants.

Venus however is quite a different story I think. You have a very dense atmosphere, a temperature of up to 450 degrees Celsius and huge vulcanic activity. The fact that Venus also has a "day" which takes longer than a Venus-year also means permanent huge storms as warmer air travels to the colder parts of the planet. And Venus has no large moon, like we do, which acts as a gravitational pull to stabilise our planet which in turns helps in having a stable climate. These are all issues which we have to tackle with terraforming.

Venus is more challenging but is the only other serious candidate for terraforming. Small (100m diameter) asteroids could be used to remove most of the atmosphere, and then flybys of objects 60 miles or more in diameter could be used to alter Venus's rotation so that it was earth-like.

[Q]

and then flybys of objects 60 miles or more in diameter could be used to alter Venus's rotation so that it was earth-like.

Yes and particularly this part will take many millenia. I mean, how many microseconds would make one such flyby of a difference?

Also, even if it works like you described, "burning up" the atmosphere would take a huge number of 100 m objects, which alone will take centuries probably. And only if we have a thin enough atmosphere we can actually start to reconstruct it to emulate Earth atmosphere, which will also take up time. An important issue here is that the vulcanic activity is also a determining factor in the atmosphere's cocktail.

Last point in this: If you use a great many 100 m objects to make impacts, wouldn't that be a great waste on materials that we could mine? And if you argue that we should only use objects that already have been stripped clean from valuable materials, wouldn't this also add a lot of time to this project?

[Lenina Rosenweg]

Kim Stanly Robinson has a realistic scenario of terraforming Mars in his trilogy (Red Mars, Blue Mars, Green Mars).If I remember right the process takes several 100 years and is largely done though genetically engineered bacteria and by diverting asteroids.

Robinson is an academic Marxist and studied under Frederic Jameson, the Marxist literary critic. His Mars books have realistic high tech as well as a Marxist analysis of class struggles. In one scene he has Martian colonists discuss the TSP and the LTV. Though out the book he has subtle Marxist puns (which I missed at the time). Martian craters and volcanoes are named "Gramsci" and "Lukacs", for example.

[Salyut]

This sounds like a project that could take many thousands if not millions of years. Are there not more direct methods to terraform Venus?

http://www.paulbirch.net/TerraformingVenusQuickly.pdf

:D

[son of man]

I think that this is such a complicated endeavour that it enters the realms of fantasy. Earth could sustain many times the population it has now if only we could figure out how to 'close the loop' and become a sustainable species. Endless production and consumption and growth for the sake of growth will screw this planet of ours beyond repair within the next hundred years.

Ecology is finite. Society is infinite as ecology allows. Economy is infinite as society allows. This equation has the making for the end of the human race.

We should think about conserving this planet as a resource for the continuation of our species and all species left on this planet.

An eco-system that is balanced and sustainable is one of the hardest things to reproduce.

[Sir Comradical]

Even if it is possible to terraform Mars, there would still be a huge gravitational difference compared to Earth. Mars has a third of earth's gravity which means that humans would not be able to survive there, we'd suffer the health problems caused by low gravity.

[son of man]

We would lose bone density. X-Games and Basketball would become much cooler though.

[mikelepore]

Isn't this what happens when an asteroid vaporizes in the atmosphere? I read somewhere that objects 100m across could eject gas from the atmosphere into space. Obviously, a great many of these would be needed, but it's not like there's a shortage of rocks in the solar system.

I'n not familiar with that. Perhaps it occurs by raising the temperature of the atmosphere, which implies that the normal distribution of molecular speeds has a greater mean, so a greater percentage of molecules exceed escape velocity. Venus already has a high temperature, and so far that hasn't caused a significant fraction of the molecules to reach escape velocity.

[ÑóẊîöʼn]

I always imagined that the best way to do this would be with directed asteroid impacts. Nuclear-powered spaceships (http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29)would be capable of delivering a large enough payload to redirect the course of asteroid.

Actually, if you're prepared to wait longer, ion thrusters (http://en.wikipedia.org/wiki/Ion_thruster) could do it. When moving asteroids, what's important is Delta V, not thrust.


I heard somewhere that this was the reason why nuclear propulsion for spacecraft was banned as part of the nuclear test ban treaty - they were afraid the Russians were going to hit the U.S. with an asteroid :).

I'm always told it due to the NPT (http://en.wikipedia.org/wiki/Nuclear_Non-Proliferation_Treaty), at least with regards to ORION propulsion.


To terraform Venus, you would first bombard the atmosphere with smaller asteroids. They would need to be small enough to burn up in the atmosphere so that the gases are ejected into space.

Why bother going to all the trouble of moving vast masses of asteroid just so you can use titanic amounts of energy to lift atmosphere out of Venus' comparitively vast gravity well? It would be far more efficient to use biological or chemical processes to lock up the excess CO2 into an inert form such as a mineral. Biological or quasi-biological processes would be especially good for this since they would be able to take advantage of exponential growth to get the job done quicker without significant additional input from human engineers.


After a significant amount of the atmosphere has been removed you would create an ocean with ice asteroids, possibly by breaking up the dwarf planet Ceres.

Capturing incoming comets would be a better bet. While Ceres has significant deposits of ice and other volatiles, it is still most composed of silicaceous and carbonaceous materials rather than water ice.

Besides, I think Ceres would be better off as a world of its own, providing a focal point for inhabitants of the asteroid belt.


Due to the topography of Venus, an ocean which covered 80% of the surface would still only account for 10% of the water on earth, having an average depth of less than 100m. Finally, you would need to create an Earth-like rotation, which could be done with flybys of massive objects (60 miles or more in diameter) - this would probably be the most difficult part.

All good, but perhaps the most potentially worrying aspect of Venus is its geological cycle. Rather than constantly resurfacing itself at plate boundariwes like the Earth does, Venus has catastrophic resurfacing events every 500 million years or so. I think it would be in our interests to determine whether Venus is due to blow its top again soon, and plan accordingly. If Venus is on the verge of another resurfacing event, it may be possible to take advantage of such a geologically brief but active period to bootstrap Venus into a more habitable state.


Mars would be easier. To add heat and greenhouse gasses, asteroids could be specifically chosen for their composition. Many objects in the outer solar system contain ammonia which could be used as both a greenhouse gas and a buffer gas for the Martian atmosphere (because ammonia contains nitrogen). The impact of the asteroid (they would need to be large enough to impact on the ground) would create heat and the released ammonia would act as a greenhouse gas and a buffer gas. To add water, bombard with ice asteroids.

What are people's thoughts on this?

Mars would definately be easier, and in the event of any terraforming project going forward that planet would be target number one.


Even if it is possible to terraform Mars, there would still be a huge gravitational difference compared to Earth. Mars has a third of earth's gravity which means that humans would not be able to survive there, we'd suffer the health problems caused by low gravity.

I haven't seen any indications that "gravitational acclimatisation" so to speak would necessarily be fatal or even debilitating - sure, somebody who was born and raised on Mars would not be able to take the strain of walking on Earth, but if you're in a situation where people can live off Earth for most of their lives, why would you want to go to Earth?

[Revy]

I think that after what will be done to the environment, we will need to terraform Earth.



I haven't seen any indications that "gravitational acclimatisation" so to speak would necessarily be fatal or even debilitating - sure, somebody who was born and raised on Mars would not be able to take the strain of walking on Earth, but if you're in a situation where people can live off Earth for most of their lives, why would you want to go to Earth?

I always thought that "gravity field generators" would be developed to avoid the gravity issue entirely (enabling long-term habitation of moons and dwarf planets as well). Not necessarily to cover the whole planet just the areas that are settled. I'm not sure if that's possible, of course.

[cska]

Kim Stanly Robinson has a realistic scenario of terraforming Mars in his trilogy (Red Mars, Blue Mars, Green Mars).If I remember right the process takes several 100 years and is largely done though genetically engineered bacteria and by diverting asteroids.

Robinson is an academic Marxist and studied under Frederic Jameson, the Marxist literary critic. His Mars books have realistic high tech as well as a Marxist analysis of class struggles. In one scene he has Martian colonists discuss the TSP and the LTV. Though out the book he has subtle Marxist puns (which I missed at the time). Martian craters and volcanoes are named "Gramsci" and "Lukacs", for example.

I tried reading Red Mars, but stopped when I saw some blatant Islamophobia.

[Technocrat]

Why bother going to all the trouble of moving vast masses of asteroid just so you can use titanic amounts of energy to lift atmosphere out of Venus' comparitively vast gravity well? It would be far more efficient to use biological or chemical processes to lock up the excess CO2 into an inert form such as a mineral. Biological or quasi-biological processes would be especially good for this since they would be able to take advantage of exponential growth to get the job done quicker without significant additional input from human engineers.



Bombardment of Venus with refined magnesium (http://en.wikipedia.org/wiki/Magnesium) and calcium (http://en.wikipedia.org/wiki/Calcium) metal could sequester carbon dioxide (http://en.wikipedia.org/wiki/Carbon_dioxide_sink) in the form of calcium (http://en.wikipedia.org/wiki/Calcium_carbonate) and magnesium carbonates (http://en.wikipedia.org/wiki/Magnesium_carbonate). About 8 × 1020 kg of calcium or 5 × 1020 kg of magnesium would be required, which would entail a great deal of mining and mineral refining.[7] (http://en.wikipedia.org/wiki/Terraforming_of_Venus#cite_note-6) 8 × 1020 kg is a few times the mass of the asteroid 4 Vesta (http://en.wikipedia.org/wiki/4_Vesta) (more than 300 miles in diameter). (http://en.wikipedia.org/wiki/Terraforming_of_Venus)
So the question is whether it is more energy efficient to refine magnesium and calcium into 'asteroids' and bombard Venus with that to cause a chemical reaction to sequester the carbon dioxide, or to bombard Venus' atmosphere with smaller asteroids to eject the atmosphere directly.

[ÑóẊîöʼn]

I always thought that "gravity field generators" would be developed to avoid the gravity issue entirely (enabling long-term habitation of moons and dwarf planets as well). Not necessarily to cover the whole planet just the areas that are settled. I'm not sure if that's possible, of course.

In the absence of technology capable of generating a gravity field without the equivalent accompanying mass, it seems unlikely. However, one can use centrifuges on the surface and rotating space habitats in orbit to simulate gravity.

Another idea I've seen is a construct kind of like a titanic roulette wheel, with a canted floor around the edge so that the colonists and other objects within it feel the combined force of the local gravity and centrifugal force.


So the question is whether it is more energy efficient to refine magnesium and calcium into 'asteroids' and bombard Venus with that to cause a chemical reaction to sequester the carbon dioxide, or to bombard Venus' atmosphere with smaller asteroids to eject the atmosphere directly.

You completely ignored the possibility of using biological (genetically engineered microorganisms) or quasi-biological processes (carbon-based nanotechnology) to do the majority of the hard work.

[Technocrat]

You completely ignored the possibility of using biological (genetically engineered microorganisms) or quasi-biological processes (carbon-based nanotechnology) to do the majority of the hard work.

No, I'm just trying to construct scenarios based on currently available technology, not speculative technology (science fiction) scenarios.

Carl Sagan had the idea of using biologically engineered microorganisms to remove carbon from the Venusian atmosphere, but that was back before we knew a lot about the atmosphere of Venus. It's pretty much been ruled out since probes have been sent.

Nanotech might be the way to go, but it's still purely speculative.

[Lenina Rosenweg]

I tried reading Red Mars, but stopped when I saw some blatant Islamophobia.

Maybe. I saw it differently. Robinson criticizes aspects of Muslim cultures but also seems to recognize a revolutionary element to Islam. Sufis play a huge role in developing his socialist Martian society.In "Years of Rice and Salt" (a complex alternate history), he has a Chinese Muslim scholar as an alternate history version of Karl Marx.

[Revy]

I can't say I support the idea of bombarding planets with asteroids. It seems counter-productive.

[Technocrat]

I can't say I support the idea of bombarding planets with asteroids. It seems counter-productive.

If you think it is a desirable goal to prolong the survival of the human race for hundreds of thousands or millions of years, then it is imperative that we settle other planets.

By studying the Earth's history, we know that multiple extinction-level events (99% of all life wiped out) have occurred throughout time. This means that it isn't a question of if, but when.

[Technocrat]

Maybe. I saw it differently. Robinson criticizes aspects of Muslim cultures but also seems to recognize a revolutionary element to Islam. Sufis play a huge role in developing his socialist Martian society.In "Years of Rice and Salt" (a complex alternate history), he has a Chinese Muslim scholar as an alternate history version of Karl Marx.

These books sound really good. I'll have to check them out.

[ÑóẊîöʼn]

No, I'm just trying to construct scenarios based on currently available technology, not speculative technology (science fiction) scenarios.

Carl Sagan had the idea of using biologically engineered microorganisms to remove carbon from the Venusian atmosphere, but that was back before we knew a lot about the atmosphere of Venus. It's pretty much been ruled out since probes have been sent.

Carl Sagan's approach required quantities of hydrogen that are now known not to be present on Venus, yes.

But there is more than one way of breaking an egg, so I'm pretty sure that a different approach to the biological solution - perhaps involving the genetic engineering of a microoorganism with a combination of xerophilic (http://en.wikipedia.org/wiki/Xerophile), lithoautotrophic (http://en.wikipedia.org/wiki/Lithoautotroph) and perhaps hyperthermophilic (http://en.wikipedia.org/wiki/Hyperthermophile) properties, that as part of its life cycle converts CO2 into calcium carbonate.


Nanotech might be the way to go, but it's still purely speculative.

Well, the same could be said for terraforming...

Regardless, if biological or nanotechnological approaches fail, there is still what I feel to be a better method than the two you have proposed - the introduction of hydrogen into Venus' atmosphere to convert the CO2 into graphite and water via the Bosch reaction (http://en.wikipedia.org/wiki/Bosch_reaction). Being the most common element in the universe hydrogen would be easy to obtain from comets or one of the gas giants, or even through capturing the solar wind.

[Technocrat]

Carl Sagan's approach required quantities of hydrogen that are now known not to be present on Venus, yes.

But there is more than one way of breaking an egg, so I'm pretty sure that a different approach to the biological solution - perhaps involving the genetic engineering of a microoorganism with a combination of xerophilic (http://en.wikipedia.org/wiki/Xerophile), lithoautotrophic (http://en.wikipedia.org/wiki/Lithoautotroph) and perhaps hyperthermophilic (http://en.wikipedia.org/wiki/Hyperthermophile) properties, that as part of its life cycle converts CO2 into calcium carbonate.

It's a possibility, but I've chosen to focus on technologies which already exist.


Well, the same could be said for terraforming...Sure, but there are some approaches which are less speculative than others.


Regardless, if biological or nanotechnological approaches fail, there is still what I feel to be a better method than the two you have proposed - the introduction of hydrogen into Venus' atmosphere to convert the CO2 into graphite and water via the Bosch reaction (http://en.wikipedia.org/wiki/Bosch_reaction). Being the most common element in the universe hydrogen would be easy to obtain from comets or one of the gas giants, or even through capturing the solar wind.This could work. It would still be a bombardment, just with hydrogen instead of the materials I suggested. Also, although hydrogen is the most common element in the universe, it is almost always bonded to something which means that energy is required to isolate the hydrogen. This means that it might turn out not to be the most efficient method.

You would also still need to do something about the rotation - I suggested the best way to do this was with flybys of objects more than 60 miles in diameter since these are large enough to alter a planet's rotation. This would be the trickiest part. If an object 60 miles or more in diameter struck the surface of Venus it would cause geological disturbances (earthquakes and volcanoes) for perhaps millions of years. One screw up with the flybys and it's game over for Venus.

[ÑóẊîöʼn]

This could work. It would still be a bombardment, just with hydrogen instead of the materials I suggested. Also, although hydrogen is the most common element in the universe, it is almost always bonded to something which means that energy is required to isolate the hydrogen. This means that it might turn out not to be the most efficient method.

The maths needs to be done for us to be sure, but my suspicion is that the superabundance of hydrogen outweighs the energy cost of extraction, refinement and transportation of comparitively far more rare elements such as calcium and magnesium.


Sure, but there are some approaches which are less speculative than others.

I certainly think genetic engineering isn't as speculative as nanotechnology or terraforming. At least we have some experience with GM.


You would also still need to do something about the rotation - I suggested the best way to do this was with flybys of objects more than 60 miles in diameter since these are large enough to alter a planet's rotation. This would be the trickiest part. If an object 60 miles or more in diameter struck the surface of Venus it would cause geological disturbances (earthquakes and volcanoes) for perhaps millions of years. One screw up with the flybys and it's game over for Venus.

Are you sure? Venus has a very thick lithosphere, which is why it does not have its crust divided into plates like Earth has. As I mentioned earlier, this thick layer creates conditions where geothermal energy builds up over hundreds of millions of years, up to the point where absorbtion capacity is exceeded and thus a major resurfacing event occurs. At least, that's the hypothesis.

I think it would be entirely possible to bombard Venus with water-rich comets (which would also provide other volatiles) in a consistent manner that increases rotational speed, and provides genetically engineered microbes the materials and energy they need to start cracking water into hydrogen and oxygen, so that with the Bosch reaction and the exponential growth patterns that organisms experience when introduced into a rich but otherwise unoccupied environment, the terraformation of Venus proceeds more swiftly than ham-handed mechanical methods can hope to achieve.

What's more, if the water-rich comets don't speed up Venus' rotation enough, we can still use the asteroid fly-past method you mentioned. If things fuck up, all is not lost; microbes are hardy little bastards. An accident may delay things, but it won't be a case of back to square one.

Of course, what's important to know is how many fly-pasts we think will be needed. That depends on our potential energy budget and how much we want to speed up the rotation. Do you think we should try to aim for as close to ~24 hours as possible, or do you think a longer period of rotation would be sufficient? I think what is important is what plant life can cope with. My estimate is that a ~72 hour rotation cycle would strike a balance between how much energy we need and survivability of plant life on the surface. Also, the fewer fly-pasts, the less chance there is of an accident.

What do you think?

[Technocrat]

The maths needs to be done for us to be sure, but my suspicion is that the superabundance of hydrogen outweighs the energy cost of extraction, refinement and transportation of comparitively far more rare elements such as calcium and magnesium.

You're probably right. It would be good to see some math confirming this. There are four proposed methods for removing the atmosphere:

1) direct bombardment of the atmosphere with smaller asteroids to eject the atmosphere directly into space
2) bombardment with refined calcium and magnesium to cause a reaction that sequesters carbon dioxide
3) bombardment with hydrogen to cause a reaction that sequesters carbon dioxide
4) introduction of biologically engineered organisms or nanotech machines that remove the atmosphere

The fourth is the most speculative since it relies on unknown technology. We could make a comparison of the other three methods just with the information we already have. The methods aren't necessarily exclusive, either.


I certainly think genetic engineering isn't as speculative as nanotechnology or terraforming. At least we have some experience with GM.The comparison is between different terraforming methods, not between terraforming and genetic engineering. Of the various proposed terraforming methods, some are less speculative because they rely on known technology that could be put to use immediately.


Are you sure? Venus has a very thick lithosphere, which is why it does not have its crust divided into plates like Earth has. As I mentioned earlier, this thick layer creates conditions where geothermal energy builds up over hundreds of millions of years, up to the point where absorbtion capacity is exceeded and thus a major resurfacing event occurs. At least, that's the hypothesis.

I think it would be entirely possible to bombard Venus with water-rich comets (which would also provide other volatiles) in a consistent manner that increases rotational speed, and provides genetically engineered microbes the materials and energy they need to start cracking water into hydrogen and oxygen, so that with the Bosch reaction and the exponential growth patterns that organisms experience when introduced into a rich but otherwise unoccupied environment, the terraformation of Venus proceeds more swiftly than ham-handed mechanical methods can hope to achieve.I don't know enough about this to say for sure, but smaller impacts might not do anything to the rotation. A lot of energy is needed to alter a planet's rotation, so much that if that energy directly impacted the planet, it would likely cause geological disturbances for hundreds of thousands if not millions of years. I don't know though, maybe the lithosphere would absorb a lot of that energy?


What's more, if the water-rich comets don't speed up Venus' rotation enough, we can still use the asteroid fly-past method you mentioned. If things fuck up, all is not lost; microbes are hardy little bastards. An accident may delay things, but it won't be a case of back to square one.

Of course, what's important to know is how many fly-pasts we think will be needed. That depends on our potential energy budget and how much we want to speed up the rotation. Do you think we should try to aim for as close to ~24 hours as possible, or do you think a longer period of rotation would be sufficient? I think what is important is what plant life can cope with. My estimate is that a ~72 hour rotation cycle would strike a balance between how much energy we need and survivability of plant life on the surface. Also, the fewer fly-pasts, the less chance there is of an accident.

What do you think?I don't know enough to say for certain, but I think a cycle as close to 24 hours as possible would be desirable just for psychological reasons. If a lot of flybys are required, you could use a 'train' of objects which would be destroyed after the rotation was adjusted.

Anyway, Mars would certainly be a lot easier. Just bombard with ammonia-containing asteroids and then bombard with ice asteroids. After it warms up enough you introduce microorganisms and plant life that speed up the process.

[Dr Mindbender]

Venus is more challenging but is the only other serious candidate for terraforming.

I dont know, Titan could be another potential candidate. It may be far further away but has a thick atmosphere and is of a planet-like size.

It is certainly less hostile than Venus.

[Technocrat]

I dont know, Titan could be another potential candidate. It may be far further away but has a thick atmosphere and is of a planet-like size.

It is certainly less hostile than Venus.

Titan is 0.0225 Earth masses, so it is probably too small to be terraformed. This doesn't mean that it couldn't be settled, though.

It's atmosphere contains cyanide which is deadly to humans. Even one breath would kill you.

One cool thing about Titan is that its thick atmosphere combined with low gravity means that a human could fly just by strapping on wings. Be careful not to get a tear in your space suit, though.

Because of the thick atmosphere, it might be possible to use oxygen as a lifting gas and build 'cloud cities'. The city's oxygen supply would also keep it afloat. This is also a proposal for settling Venus. There is a certain point in the Venusian atmosphere where temperatures are Earth like and humans could go outside with just a breathing mask (and protection from the acid rain). Obviously, terraforming would be more desirable long-term.

[NGNM85]

If you think it is a desirable goal to prolong the survival of the human race for hundreds of thousands or millions of years, then it is imperative that we settle other planets.

By studying the Earth's history, we know that multiple extinction-level events (99% of all life wiped out) have occurred throughout time. This means that it isn't a question of if, but when.

Absolutely. The future of the human species, or, rather, the possibility of there being a future for the human race, entirely depends on it.

[mikelepore]

I have a hunch that Mars won't be terraformed at all. Instead people will probably gradually cover the surface of the planet with a large artificial building that encloses the liveable environment and blocks solar radiation. Some of that structure will probably have a transparent ceiling so plants can be grown inside it. The building will probably be made of connected cells, so that any cell that gets punctured by a meteoroid can be sealed off until it is repaired.

[Technocrat]

I have a hunch that Mars won't be terraformed at all. Instead people will probably gradually cover the surface of the planet with a large artificial building that encloses the liveable environment and blocks solar radiation. Some of that structure will probably have a transparent ceiling so plants can be grown inside it. The building will probably be made of connected cells, so that any cell that gets punctured by a meteoroid can be sealed off until it is repaired.

Somehow, this seems less feasible and desirable than making Mars earth-like.

I imagine that Titan could be colonized by floating cities (using oxygen as a lifting gas), that could one day encompass the majority of its surface. Similar proposals for settling Venus have been suggested, but I'm in favor of terraforming. Titan is one example where terraforming isn't likely, so an artificial environment would be needed.

[Revy]

If you think it is a desirable goal to prolong the survival of the human race for hundreds of thousands or millions of years, then it is imperative that we settle other planets.

By studying the Earth's history, we know that multiple extinction-level events (99% of all life wiped out) have occurred throughout time. This means that it isn't a question of if, but when.

I understand that, but that's not at all relevant to what I was saying. I just doubt that bombarding a planet with asteroids is a desirable way to help make it Earth-like. That would just cause lots of destruction of the planet's surface. If there are important elements in these asteroids, there are ways to spread them in the planet's atmosphere that don't involve asteroid impacts.

[Technocrat]

I understand that, but that's not at all relevant to what I was saying. I just doubt that bombarding a planet with asteroids is a desirable way to help make it Earth-like. That would just cause lots of destruction of the planet's surface. If there are important elements in these asteroids, there are ways to spread them in the planet's atmosphere that don't involve asteroid impacts.

This is something that astrophysicists came up with, not me. It's been suggested as a way to terraform both Mars and Venus.

Why does it matter if we cause destruction to the planet's surface if there is nothing living there? In the case of Mars it would be desirable as an impact on the planet's surface would cause the energy to be released as heat. Asteroids could also be chosen for their composition (ammonia) to add greenhouse gas. This is probably the easiest and most direct way of terraforming Mars with available technology.