He talks about it here at 2 minutes in, just says "The fast way is to drop thermonuclear weapons on the poles":
Getting lots of questions about it here today as a result.
I know he is probably at least half joking in the video, but his remarks have been taken seriously by some reporters, e.g. in the Independent, Want to make Mars hospitable? Drop nuclear bombs, says Elon Musk and Elon Musk says nuking Mars is the quickest way to make it livable - CNET and many other headlines of that nature today.
And it's an interesting question, so I think deserves a detailed serious answer :).
First, I've never seen any paper suggesting nuclear weapons could terraform Mars quickly.
I've never seen any serious suggestion to use nukes. Mirrors yes, impacting comets yes, artificial greenhouse gases yes, but nukes, they are just not powerful enough, and anyway the atmosphere still would need extra warming even if you did liberate the CO2 to keep it liberated.
And anyway, it wouldn't work. Not make it habitable as in Earth habitable or even close.
If you went all out and exploded thousands of 1 gigaton bombs on Mars, what it could do is briefly release a lot of dry ice (CO2) into the atmosphere as CO2, also water vapour, which would make the Mars atmosphere briefly a bit thicker. But nowhere near as thick as Earth. This happens naturally whenever large comets hit the Mars poles, and as you can see, they haven't made it into a habitable planet.
The other effect would be to create a lake at the poles. Which would soon freeze over. But below the insulating covering of ice, it would remain liquid for a while.
But it would be much better to deflect a large comet to hit Mars if you want that effect.
Even quite small bolides hitting Earth atmosphere release the equivalent of small nuclear bombs in terms of the amount of energy released into the upper atmosphere when they create bright fireballs briefly brighter than a full moon.
To interpret this table, a kiloton is about 4,184 gigajoules. So the ones labeled as 10,000 gigajoules are in the kilotons range TNT equivalent
Mars is closer to the asteroid belt and gets hit about ten times more often than Earth, and with its thin atmosphere, then even small asteroids get all the way to the surface. On Mars these wouldn't be air bursts, they'd be surface hits, and there would be ten times as many of them as for Earth.
It gets hit by meteorites large enough to create a small crater 200 times every year.
It gets hit by the equivalent of a 1 megaton impact every 3 years estimated . On Earth the equivalent figure is once every 15 years.
It gets hit by a 10 megaton impact every century. See Earth and Mars crater-size frequency distribution and impact rates:theoretical and observational analysis
So, it gets hit by impacts with the equivalent of multi-kiloton nuclear weapon impacts frequently and multi-megaton level impacts would be common.
The largest nuclear weapon ever detonated on the Earth, the Tsar Bomba, had a yield of 40 megatons.
This is its bomb casing (File:Tsar Bomba Revised.jpg)
And the fireball:
The Tsara Bomba fireball, about 8 km in diameter. (File:Tsar01.jpg)
A 130 meter diameter meteorite hitting Earth has a similar yield to the Tsara Bomba of about 60 megatons (though in the case of Earth much of it would be dissipated in the atmosphere on the way down)..
Conceivably we could build a 1 gigaton nuclear weapon in the future with 25 times the yield of the Tsara Bomba..
But a 1 km diameter comet has a yield of around 100 gigatons.
A 10 km diameter comet has a yield of around 100,000 gigatons.
On Mars, the impact velocity is roughly halved for short period comets (not so much for long period comets) - that still makes the yield around 25 gigatons and about 25,000 gigatons respectively.
So you'd need 25,000 gigaton bombs each one 25 times more powerful than the largest nuclear weapon ever built, to equal the effect of a single one 10 km diameter comet hitting the poles of Mars. And that's a size of comet that would hit Mars from time to time.
I got those figures from Defending Planet Earth - page 36 - by the Space Studies board. Other sources give somewhat varying figures, but whether it is 60,000 or 100,000 gigatons is neither here nor there.
(I'll see if I can find statistics for the megatons and expected frequency of impacts of 10 km comets for Mars and update this answer, meanwhile this is plenty to give a first idea of what is involved)
So, if you think that nuclear bombs would jump start a thicker atmosphere on Mars, why haven't asteroid and comet impacts done that already?
We can also come at this another way. The latent heat of melting for ice is quite high. 334 Kj/kg.
A kiloton is about 4,184 gigajoules, so that's enough to melt 4184000000/334 kg or about 12,500,000 kg. Or about 12,500 cubic meters.
A Tsar Bomba at 40 megatons, if all the energy went into melting water and none into heating up rock or dissipated into the atmosphere could melt 40,000 times that, so given that there are a billion cubic meters in a cubic kilometer, it could melt half a cubic kilometer of water (500 million tons)
Spread over the entire surface of Mars, surface area of 144.8 million square kilometers, then that would be equivalent to a layer of 0.0000035 meters, or about 3.5 microns of water.
The water currently in the Mars atmosphere has equivalent of 10-20 microns (though varying regionally, seasonally, and from day to night). Page on sciencedaily.com
So one Tsar Bomba would increase the amount of water vapour temporarily by about a third, if it all went into melting ice - but - in practice only a tiny fraction of it would do that..
If we used 25,000 gigaton bombs (625,000 Tsar Bombas), the equivalent of our 10 km diameter comet, this could melt the equivalent to a layer of about 2.2 meters of water over the surface of Mars.
So this would melt a fifth of the estimated 11 meters of water equivalent over the surface of Mars thought to be available on Mars according to one estimate.
But - in practice nothing like that amount of energy would go into melting the ice. And any water that got into the atmosphere would almost immediately condense out again as ice, or penetrate into the dry equatorial sands and be lost. And much of that water would remain on the surface at the impact point as a lake that would freeze over.
The idea I think is to try to kickstart a greenhouse effect, not make significant changes to Mars right away. I can't find much about this, it's not the most usual suggestion for a way to heat up Mars.
Michio Kaku briefly mentions nuclear bombs here:
Just as a passing remark, I doubt if he means that nuclear bombs by themselves could do it.
Situation is much the same for dry ice, latent heat of melting / sublimation is 184, if all the energy went into sublimating dry ice, then each Tsar Bomba would liberate 275 million tons of CO2, just a tiny fraction of the 25 trillion tons (teratons) of the Mars atmosphere. So again you'd need millions of these to start to make a significant difference, with all of the energy somehow focused into liberating dry ice into CO2.
So, it's not going to do that much directly. Hope has to be to somehow initiate a runaway feedback reaction. But the amounts are rather small for that also from a few hundred thousand nuclear bombs.
If you think liberating a small amount of water or dry ice from the ice caps like this could cause a runaway greenhouse effect of some sort - well why hasn't it happened already with comet impacts?
When Comet Sliding Spring was first discovered, then for a time they thought it was going to hit Mars, and then could have done this experiment for us naturally, but it missed.
The subsurface lake would be a temporary habitat for life on Mars a bit like the subglacial lakes in Antarctica. This happens from time to time and is one of the possible habitats in present day Mars for life there.
The models suggest that if a comet a few kilometers in diameter hit a high lattitude region of Mars, the result would be a crater 30 - 50 km in diameter and an underground hydrothermal system that remains liquid for thousands of years.
It would be a habitat for microbes. An anaerobic lake, so no oxygen, even if you have hydrothermal vents (the Antarctic lakes are nitrogen and oxygen rich, even hyperoxygenated, through the effect of dissolved air getting into the lakes as the ice at the bottom melts - but on Mars the same process if it happened would make it CO2 rich, not oxygen rich).
There is a lot more to it anyway. First, Mars gets half the sunlight levels of Earth.
Terraforming suggestions typically add large mirrors in space, or greenhouse gases such as methane to compensate for that.
Then, CO2 is poisonous to humans, at levels above 1%. So somehow you want to convert all that CO2 into organics and oxygen, or the most you can have live there are trees. But to do that takes a huge amount of energy, or else, you use photosynthesis. But to generate all that oxygen you need to take the carbon out of the atmosphere permanently, not just circulate it around as plants usually do, it eventually returns as they decay.
So you need to grow enough plants to cover the entire surface of Mars with a layer several meters thick of organics to sequester all that carbon. This part of the process, Chris McKay estimated would take about 100,000 years - because it has about half the light levels of Earth, and a third of the gravity so that it needs to have three times the mass of oxygen per square meter for the same atmospheric partial pressure.
Then, humans don't do well in an environment of pure oxygen long term, we suffer from oxygen poisoning unless the atmosphere is very thin and even then long term like for years, wouldn't want to live in a pure oxygen low pressure atmosphere - and anyway it is also a major fire hazard if the entire atmosphere was oxygen, supposing you could do it.
So, you'd want a buffer gas. Mars has some argon but not huge amounts. It originally had lots of nitrogen but it is gone, perhaps turned into rock? So you have to somehow liberate or find huge quantities of nitrogen to use as a buffer gas for the atmosphere.
And it probably doesn't have enough water either, 11 meters global equivalent layer of ice - which may sound a lot but remember, you've got equatorial regions that are dry to depths of over a hundred meters, probably hundreds of meters - melt that ice and most of it would just sink into the equatorial dry sands.
There are ideas for all this, but it involves megaengineering - importing water from comets. Could get the nitrogen that way too using methane rich comets from the outer solar system. Large mirrors in space. Etc etc.
Then you have the problem that the planet you just terraformed in this way - with its greenhouse gases or mirrors, needs continual support by high technology to keep it running. If you can terraform it as quickly and easily as that, it can unterraform just as quickly. And long term it loses water vapour from the atmosphere. You've still got the solar storms. You've got the high impact rate because it is closer to the asteroid belt.
With the level of technology needed for terraforming Mars - why not just move all those comets and other resources into close to Earth orbit instead and build space habitats? And use the technology for mirrors around Mars to build thin film mirrors to concentrate sunlight on solar panels in orbit around Earth and beam the energy to Earth and solve our energy problems?
It doesn't make a lot of sense to use that technology to pour water onto a desert planet as part of a hundred thousand year project.
Well not yet anyway, we are at the stage, surely, of attempting multi-decade rather than hundreds of thousands of years projects.
And the thing is - our failed primitive attempts on Mars right now could easily mess up the planet in such a way as to make future terraforming or whatever else we want to do there much harder.
See Trouble With Terraforming Mars
To Terraform Mars with Present Technology - Far into Realms of Magical Thinking - Opinion Piece
Imagined Colours Of Future Mars - What Happens If We Treat A Planet As A Giant Petri Dish?
Citations for the impact lake if you want to look at the scholarly papers (but these are mainly behind paywalls):
As usual, if you spot anything at all to correct in this, however minor, don't hesitate to say in the comments :).
Getting lots of questions about it here today as a result.
I know he is probably at least half joking in the video, but his remarks have been taken seriously by some reporters, e.g. in the Independent, Want to make Mars hospitable? Drop nuclear bombs, says Elon Musk and Elon Musk says nuking Mars is the quickest way to make it livable - CNET and many other headlines of that nature today.
And it's an interesting question, so I think deserves a detailed serious answer :).
First, I've never seen any paper suggesting nuclear weapons could terraform Mars quickly.
I've never seen any serious suggestion to use nukes. Mirrors yes, impacting comets yes, artificial greenhouse gases yes, but nukes, they are just not powerful enough, and anyway the atmosphere still would need extra warming even if you did liberate the CO2 to keep it liberated.
And anyway, it wouldn't work. Not make it habitable as in Earth habitable or even close.
WHAT IT COULD DO - CREATE A TEMPORARY ICE COVERED LAKE AT THE POLES
If you went all out and exploded thousands of 1 gigaton bombs on Mars, what it could do is briefly release a lot of dry ice (CO2) into the atmosphere as CO2, also water vapour, which would make the Mars atmosphere briefly a bit thicker. But nowhere near as thick as Earth. This happens naturally whenever large comets hit the Mars poles, and as you can see, they haven't made it into a habitable planet.
The other effect would be to create a lake at the poles. Which would soon freeze over. But below the insulating covering of ice, it would remain liquid for a while.
But it would be much better to deflect a large comet to hit Mars if you want that effect.
Even quite small bolides hitting Earth atmosphere release the equivalent of small nuclear bombs in terms of the amount of energy released into the upper atmosphere when they create bright fireballs briefly brighter than a full moon.
Mars is closer to the asteroid belt and gets hit about ten times more often than Earth, and with its thin atmosphere, then even small asteroids get all the way to the surface. On Mars these wouldn't be air bursts, they'd be surface hits, and there would be ten times as many of them as for Earth.
It gets hit by meteorites large enough to create a small crater 200 times every year.
One of many fresh impact craters on Mars spotted from orbit. It gets hit by 200 meteorites large enough to create small craters like this every year (much higher frequency than Earth because closer to the asteroid belt, and also thinner atmosphere). See Pow! Mars Hit By Space Rocks 200 Times a Year
It gets hit by the equivalent of a 1 megaton impact every 3 years estimated . On Earth the equivalent figure is once every 15 years.
It gets hit by a 10 megaton impact every century. See Earth and Mars crater-size frequency distribution and impact rates:theoretical and observational analysis
So, it gets hit by impacts with the equivalent of multi-kiloton nuclear weapon impacts frequently and multi-megaton level impacts would be common.
YIELD IN GIGATONS EQUIVALENT OF A COMET IMPACT ON THE MARS POLES
The largest nuclear weapon ever detonated on the Earth, the Tsar Bomba, had a yield of 40 megatons.
This is its bomb casing (File:Tsar Bomba Revised.jpg)
A 130 meter diameter meteorite hitting Earth has a similar yield to the Tsara Bomba of about 60 megatons (though in the case of Earth much of it would be dissipated in the atmosphere on the way down)..
Conceivably we could build a 1 gigaton nuclear weapon in the future with 25 times the yield of the Tsara Bomba..
But a 1 km diameter comet has a yield of around 100 gigatons.
A 10 km diameter comet has a yield of around 100,000 gigatons.
On Mars, the impact velocity is roughly halved for short period comets (not so much for long period comets) - that still makes the yield around 25 gigatons and about 25,000 gigatons respectively.
So you'd need 25,000 gigaton bombs each one 25 times more powerful than the largest nuclear weapon ever built, to equal the effect of a single one 10 km diameter comet hitting the poles of Mars. And that's a size of comet that would hit Mars from time to time.
I got those figures from Defending Planet Earth - page 36 - by the Space Studies board. Other sources give somewhat varying figures, but whether it is 60,000 or 100,000 gigatons is neither here nor there.
(I'll see if I can find statistics for the megatons and expected frequency of impacts of 10 km comets for Mars and update this answer, meanwhile this is plenty to give a first idea of what is involved)
So, if you think that nuclear bombs would jump start a thicker atmosphere on Mars, why haven't asteroid and comet impacts done that already?
LATENT HEAT OF MELTING FOR ICE
We can also come at this another way. The latent heat of melting for ice is quite high. 334 Kj/kg.
A kiloton is about 4,184 gigajoules, so that's enough to melt 4184000000/334 kg or about 12,500,000 kg. Or about 12,500 cubic meters.
A Tsar Bomba at 40 megatons, if all the energy went into melting water and none into heating up rock or dissipated into the atmosphere could melt 40,000 times that, so given that there are a billion cubic meters in a cubic kilometer, it could melt half a cubic kilometer of water (500 million tons)
Spread over the entire surface of Mars, surface area of 144.8 million square kilometers, then that would be equivalent to a layer of 0.0000035 meters, or about 3.5 microns of water.
The water currently in the Mars atmosphere has equivalent of 10-20 microns (though varying regionally, seasonally, and from day to night). Page on sciencedaily.com
So one Tsar Bomba would increase the amount of water vapour temporarily by about a third, if it all went into melting ice - but - in practice only a tiny fraction of it would do that..
If we used 25,000 gigaton bombs (625,000 Tsar Bombas), the equivalent of our 10 km diameter comet, this could melt the equivalent to a layer of about 2.2 meters of water over the surface of Mars.
So this would melt a fifth of the estimated 11 meters of water equivalent over the surface of Mars thought to be available on Mars according to one estimate.
But - in practice nothing like that amount of energy would go into melting the ice. And any water that got into the atmosphere would almost immediately condense out again as ice, or penetrate into the dry equatorial sands and be lost. And much of that water would remain on the surface at the impact point as a lake that would freeze over.
The idea I think is to try to kickstart a greenhouse effect, not make significant changes to Mars right away. I can't find much about this, it's not the most usual suggestion for a way to heat up Mars.
Michio Kaku briefly mentions nuclear bombs here:
Just as a passing remark, I doubt if he means that nuclear bombs by themselves could do it.
Situation is much the same for dry ice, latent heat of melting / sublimation is 184, if all the energy went into sublimating dry ice, then each Tsar Bomba would liberate 275 million tons of CO2, just a tiny fraction of the 25 trillion tons (teratons) of the Mars atmosphere. So again you'd need millions of these to start to make a significant difference, with all of the energy somehow focused into liberating dry ice into CO2.
So, it's not going to do that much directly. Hope has to be to somehow initiate a runaway feedback reaction. But the amounts are rather small for that also from a few hundred thousand nuclear bombs.
If you think liberating a small amount of water or dry ice from the ice caps like this could cause a runaway greenhouse effect of some sort - well why hasn't it happened already with comet impacts?
COMET SLIDING SPRING
When Comet Sliding Spring was first discovered, then for a time they thought it was going to hit Mars, and then could have done this experiment for us naturally, but it missed.
The subsurface lake would be a temporary habitat for life on Mars a bit like the subglacial lakes in Antarctica. This happens from time to time and is one of the possible habitats in present day Mars for life there.
The models suggest that if a comet a few kilometers in diameter hit a high lattitude region of Mars, the result would be a crater 30 - 50 km in diameter and an underground hydrothermal system that remains liquid for thousands of years.
It would be a habitat for microbes. An anaerobic lake, so no oxygen, even if you have hydrothermal vents (the Antarctic lakes are nitrogen and oxygen rich, even hyperoxygenated, through the effect of dissolved air getting into the lakes as the ice at the bottom melts - but on Mars the same process if it happened would make it CO2 rich, not oxygen rich).
LOTS MORE TO TERRAFORMING MARS
There is a lot more to it anyway. First, Mars gets half the sunlight levels of Earth.
Terraforming suggestions typically add large mirrors in space, or greenhouse gases such as methane to compensate for that.
Then, CO2 is poisonous to humans, at levels above 1%. So somehow you want to convert all that CO2 into organics and oxygen, or the most you can have live there are trees. But to do that takes a huge amount of energy, or else, you use photosynthesis. But to generate all that oxygen you need to take the carbon out of the atmosphere permanently, not just circulate it around as plants usually do, it eventually returns as they decay.
So you need to grow enough plants to cover the entire surface of Mars with a layer several meters thick of organics to sequester all that carbon. This part of the process, Chris McKay estimated would take about 100,000 years - because it has about half the light levels of Earth, and a third of the gravity so that it needs to have three times the mass of oxygen per square meter for the same atmospheric partial pressure.
Then, humans don't do well in an environment of pure oxygen long term, we suffer from oxygen poisoning unless the atmosphere is very thin and even then long term like for years, wouldn't want to live in a pure oxygen low pressure atmosphere - and anyway it is also a major fire hazard if the entire atmosphere was oxygen, supposing you could do it.
So, you'd want a buffer gas. Mars has some argon but not huge amounts. It originally had lots of nitrogen but it is gone, perhaps turned into rock? So you have to somehow liberate or find huge quantities of nitrogen to use as a buffer gas for the atmosphere.
And it probably doesn't have enough water either, 11 meters global equivalent layer of ice - which may sound a lot but remember, you've got equatorial regions that are dry to depths of over a hundred meters, probably hundreds of meters - melt that ice and most of it would just sink into the equatorial dry sands.
There are ideas for all this, but it involves megaengineering - importing water from comets. Could get the nitrogen that way too using methane rich comets from the outer solar system. Large mirrors in space. Etc etc.
Then you have the problem that the planet you just terraformed in this way - with its greenhouse gases or mirrors, needs continual support by high technology to keep it running. If you can terraform it as quickly and easily as that, it can unterraform just as quickly. And long term it loses water vapour from the atmosphere. You've still got the solar storms. You've got the high impact rate because it is closer to the asteroid belt.
With the level of technology needed for terraforming Mars - why not just move all those comets and other resources into close to Earth orbit instead and build space habitats? And use the technology for mirrors around Mars to build thin film mirrors to concentrate sunlight on solar panels in orbit around Earth and beam the energy to Earth and solve our energy problems?
It doesn't make a lot of sense to use that technology to pour water onto a desert planet as part of a hundred thousand year project.
Well not yet anyway, we are at the stage, surely, of attempting multi-decade rather than hundreds of thousands of years projects.
And the thing is - our failed primitive attempts on Mars right now could easily mess up the planet in such a way as to make future terraforming or whatever else we want to do there much harder.
See Trouble With Terraforming Mars
To Terraform Mars with Present Technology - Far into Realms of Magical Thinking - Opinion Piece
Imagined Colours Of Future Mars - What Happens If We Treat A Planet As A Giant Petri Dish?
Citations for the impact lake if you want to look at the scholarly papers (but these are mainly behind paywalls):
- Starting conditions for hydrothermal systems underneath Martian craters: Hydrocode modeling Pierazzo, E., Artemieva, N.A., and Ivanov, B.A., 2005, from Large Meteorite Impacts III, Issue 384, p 444 edited by Thomas Kenkmann, Friedrich Hörz, Alexander Deutsch Geological Society of America, 1 Jan 2005 (pdf, earlier version with colour graphics)
- "Impact melt and uplifted basement heat sources in craters >50 km in diameter should be sufficient to drive substantial hydrothermal activity and keep crater lakes from freezing for thousands of years, even under cold climatic conditions" Location and Sampling of Aqueous and Hydrothermal Deposits in Martian Impact Craters Horton E. Newsom, Justin J. Hagerty, and Ivan E. Thorsos. Astrobiology. March 2001, 1(1): 71-88. doi:10.1089/153110701750137459.]
- Impact crater lakes on Mars, Horton E. Newsom, Gregory E. Brittelle, Charles A. Hibbitts, Laura J. Crossey, Albert M. Kudo, Journal of Geophysical Research: Planets (1991–2012) Volume 101, Issue E6, pages 14951–14955, 25 June 1996 DOI: 10.1029/96JE01139
- Lakes on Mars (Google eBook), Nathalie A. Cabrol, Edmond A. Grin, Elsevier, 15 Sep 2010
As usual, if you spot anything at all to correct in this, however minor, don't hesitate to say in the comments :).
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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