The first is how big does the structure need to be? I can buy a 1 Tesla magnet online right now but that's probably not what they're thinking of. Would we need a city-sized coil or something like that?
The second is the time scale. They say that the temperature could rise by 4 Celsius and trigger a greenhouse effect, but is that an immediate effect (10 years or so) or century-scale effect? I'm hoping the scientists put out a paper because I'd love to learn more about the specifics of their proposal.
Assuming you had no losses, so say ideal superconducting coils, that's how much energy you have to dump into magnetic field. You can do this as slow as you like, so with 1/10 the US electrical energy production it would take 10 years to build up that magnetic field. Hypothetically, if you had thin-film plastic PV cells (like cellophane thin to be reasonable to build and get into space) with 100% efficiency covering the footprint of this system (Mars) you could generate enough power to charge up this field in 471 seconds:
Of course the big story here is that efficient thin film solar in space could generate obscene amounts of power.
I'm not sure on the depth of the field volume required, so that might make it easier, too.
Presumably, though, some of the power generated could be used to accelerate propellant to compensate.
For a deeper cut, see https://physics.stackexchange.com/questions/94273/what-force...
We should be so lucky. Planetary scale can be rather large and slow. For instance the oxygenation of the Earth's atmosphere took hundreds of millions of years
It's extremely unlikely that we can pull it off in a human lifespan but I would bet that planetary oxygenation is possible given a few millennia
The industrial revolution has been going since before 1800 https://en.wikipedia.org/wiki/Industrial_Revolution
So, yes if the magnet dipole were the size of Mars and it needed to be 5mT=500,000nT at 320 Mars diameters, then roughly (ignoring higher order effects) you would need an average 16kT around the surface poles, which isn't possible with current technology.
At 1 Tesla you would want to cover an area 50 times the diameter than Mars? That's pretty fanciful.
OK, either my simple calculations are bunk, or this is a truly crazy idea.
So with the mentioned 1-2 Tesla starting field, we end up and a cube law reducing the strength 200x at 6 times the distance, and a 1.5km moment. That would require at least 2-3km^2 of 1T magnets. Ignoring the support structure that would have a volume of ~10^10 cm^3 and weigh 100ktons, but only cost $100B on Earth at todays Samarium Cobalt pricing, if the market wasn't highly distorted.
Sounds more reasonable...
He said the best plan for a shield for Mars is a 500,000 nanoTesla field at L1 which is 320 Mars radii away from Mars.
Maybe I am misunderstanding what he is saying or pronouncing, nanoTesla i.e. billionths of a Tesla?
I mean, I know that's a stable Lagrange point, but you have to wonder if it could end up moving and or spinning around after enough solar flares hit it and what that would do.
It takes on the order of hundreds of millions of years to lose that much atmosphere.
Or we could at least use this as an indicator that the problem is solvable over a few centuries and start nuking. Better sooner than later!
I'm just amused by this conversion. Who is this for? Are there people who know one unit of magnetic flux and not the other?
Edit: Anyway, I do agree that the priority ought to be displacing carbon emissions, and removing CO2 from the atmosphere.
There's nothing inherently different about a planet's magnetic field pushing the stellar/solar wind out of its way and e.g. a boat on water pushing water out of the way. Terms like magneto(sheath|pause|tail) are just labels for different parts of the "wake".
Yes there is. Magnetohydrodynamics are more complex than hydrodynamics because of the electromagnetic effects.
Yes, there is the fluid component, but in addition to that, there are the bits coming from electromagnetics. Arising from Maxwell's "a moving charge creates a magnetic field..." and "a force is induced on a charge moving through a magnetic field "etc.
I.e. Atoms repel each other because of their magnetic fields, and depending on their polarity and spin in the aggregate they can produce bigger and more complex magnetic fields, such as the ones analyzed by magnetohydrodynamics.
So there would be a major improvement in keeping heat low/improving system efficiency or to transfer heat away without cooking the crew after the turn the thing on.
Edit: the permanent magnet will feel a force applied against it in the opposite direction, of course. In space, that's have to be countered by rockets though, not electrically in the current running through the superconductor, right?
Because the incoming electrically charged particle induces current in the coils of the electromagnet.
A permanent magnet does not have to deal with that - even if there is current it doesn't affect the magnetism in a permanent way.
Think about an electric solenoid: A stationary electromagnet does not consume power, a moving one does as it acts on the external magnets.
If it doesn't require an atmosphere, could this approach be used to build a magnetospher around the moon? It feels like colonizing the moon first is a much easier and more useful problem to tackle. Once we have a moon colony you can crack water to make fuel and then go "where ever" you'd like - other asteroids, or mars. The moon is much closer and easier to get to, though maybe people need the "excitement" that travel to Mars connotates.
This image explains it better than I can: https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/2017...
I don't think an approach like this would work for the moon, because there's no stable Lagrange point between the moon and the sun. (And even if we did build a magnetic shield for the moon somehow, I think it's still too small to accumulate an atmosphere.)
Beyond that, the moon is generally much less suited for long term habitation than Mars is for several reasons. I won't get into details about that right here (unless you want me to) and Mars isn't exactly a cakewalk either, but the moon poses a more significant challenge in many ways.
That said, I welcome any kind of manned missions/outposts/colonies etc, whether the be on the moon or Mars or somewhere else entirely. I just believe that the payoff for starting on Mars could be much greater than doing the same on the moon.
No, it's the other way around -- for a sustainable atmosphere, one needs a magnetic field.
> If it doesn't require an atmosphere, could this approach be used to build a magnetospher around the moon?
That would have an effect on surface radiation from charged particles, but the moon can't have an earth-like atmosphere because of its low gravity. So the payoff is smaller.
More details: http://arachnoid.com/restoring_mars
The energy in a uniform field is very simple to calculate: a sphere with a radius of 6371 km (radius of earth, diameter of mars) and 50,000 nT would store about a 10^18 joules, about 6.5% of US annual electricity consumption. At the extremal 500,000 nT that would be 10^20 joules, around 2x the global electricity consumption.
A dipole field would require ~10x more energy, a zetajoule. That's around 2x the global human annual energy consumption, including for heat/transport/industry/etc.
For comparison earths magnetic field is 31,000 nanoTesla and they are putting it at L1 so a weaker/smaller field to do the same job.
50,000 nT was their suggestion of what actually starts providing relevant protection. 5,000 nT was where they started seeing it at all, which would be 10^16 joules/2 megatons of TNT. I believe the massively stronger field is needed because the protection they are looking at for terraforming would need to be much better than Earth's. We still lose 94,608 tonnes of hydrogen annually to atmospheric escape, despite having 263% stronger gravity.
The only other place you could have it would be directly on mars, where it would have to be much larger.
Bonus: Could we make it big enough to encompass the moon?
Of course diverting that much solar wind would create a force on the object. In the paper above that force is used to accelerate a craft. It'd be some handful of newtons at 20 km and linearly more to do what this project wants. One way you might get around that is to "lean into" the wind by going down the sun-side of the L1 halo orbit and allowing the force from the diverted solar wind to counter the sun's gravity's acceleration.
But for the vast majority of the lost Mar's atmosphere the kinetic energy needed to achieve escape velocity is not from impact with solar wind ions or other solar wind related/magnetic field means. All those hereafter referenced under the umbrella term "jeans escape".
Instead the majority of the kinetic energy needed comes from the ejected electrons from the sun's light ionizing the upper atmosphere. That ejected electron has quite a bit and it is distributed to the ions it later interacts with and as those ions interact with others. If there was no solar wind at all the rate of atmospheric loss at Mars would drop but not significantly if the sun still shone upon it.
That isn't to say that, having no magnetosphere, Mars (or Venus) does not lose an additional small amount of it's atmosphere to jeans escape mechanisms. But that amount is limited due to the currents created in the upper atmosphere by photoionization creating their own local magnetic field. That creates a bow shock about the ionopause which slows the incoming solar wind down such that it's constituent ions no longer have the energy needed to deliver the boost required for escape. And because of the induced magnetic field other solar wind magnetic field based mechanisms which would pick-up the ions ionized by the sun's light are mitigated.
I love the idea of this but it isn't going to make Mars have a decent atmospheric pressure in just some years.
On a (much) lighter note, I was thinking if you put these artificial magnetospheres all over the inner system and then coordinated turning them on and off you could "paint" the termination shock surface of the heliosphere with different scales of tubulence in charge density. It'd be a multi-hundred AU wide screen visible only from very far away with sensitive polarimeters (detecting the changes in lines of sight charge density through faraday rotation). Might be a decent way to METI since it'd not require much energy or high angular resolution at the other end.
tldr: It's technically and economically feasible. But it doesn't work like suggested for atmospheric protection because almost all the mass loss is from light caused photoionization, not the solar wind (and other Jeans escape mechanisms).
Source? That's in direct contradiction with the article stating:
> In addition to determining that solar wind was responsible for depleting Mars' atmosphere, these probes have also been measuring the rate at which it is still being lost today.
You seem to be forgetting that Mars has a very thin atmosphere, so there is no appreciable bow shock created. The upper atmosphere will protect itself only if it's dense enough to create sufficiently strong eddies to deal with peak solar wind. Mars' atmosphere is not dense enough. Venus' is, maybe that's what you're thinking of? Adding a synthetic magnetosphere to Venus will not accomplish much due to the effect you're describing.
And besides, do you really think the Director of Planetary Science of NASA, who recently launched MAVEN to study exactly this topic, somehow missed the core assumption of this project?
You're making a very strong claim, so please provide strong proof of the following:
- Show that "But for the vast majority of the lost Mar's atmosphere the kinetic energy needed to achieve escape velocity is not from impact with solar wind ions or other solar wind related/magnetic field means" -- NASA seems to disagree
- Show that photoionization accounts for "the majority of kinetic energy needed"
- Show that bow shock in Mars' thin atmosphere is sufficiently strong to deflect peak solar wind activity
I don't believe any of those three points are provable for Mars. I believe you can show that bow shock is sufficiently strong on Earth and Venus, but not Mars. I believe you can show that Jeans escape is small on Venus because of the composition of the atmosphere, but not Mars.
I really don't think this is a good idea, unless we want a massive object accelerated to a significant percentage of c to get lobbed our way. :)
Disregarding the effects on atmosphere loss, wouldn't a machine like this eventually be more or less essential if humans ever decide to move in long term? At least, if we want to hang out on the surface (in bubbles, of course).
There is also a really nice MAD effect where the window where you can hit a solar system without getting hit back is extremely short, like a century perhaps. Longer than that and we send a probe to the cannonball and turn it into diffuse gray goo that the solar wind blows away when it enters the system, and we return fire 1000 times over, so any logical civilization would send in the asteroid weapons much earlier, like the first time they sniff RF transmissions or the first dark side of the planet electric lights.
In the The Killing Star, our doom was already sealed by "Star Trek" :(
I think it's more practical in the long term to create a magnetic field at Mars itself. Using future technology on a scale unimaginable at present (and similar to that proposed in the linked article), we could magnetize Mars' (now-solid) ferrous materials by the onetime application of a very strong magnetic field.
Mars once had a dynamic magnetic field like ours, but Mars' liquid ferrous materials solidified as the planet cooled, which caused its field to disappear. A permanent field could be created by the deliberate application of a strong temporary field that would magnetize the planet's ferrous materials.
ISTR the Swordholder did something similar in Death's End. The purpose wasn't "light", however.
Taking it even further (and more absurd) the interface between the heliosphere and the interstellar medium (ISM) lets in matter mostly along a curved path at the bow who's size and orientation is defined by the relative magnetic vector orientations of the heliosphere and the ISM. This was a recent discovery by the IBEX interstellar neutral atom monitor. If you could get the artificial magnetospheres to influence the magnetic field around the region in the bow where this happens (by controlling the magnetic field in the plasmoids your artificial magnetospheres sends off with the wind) you might be able to control the direction interstellar neutral atoms come in at. And that'd allow you to apply arbitrary (small) force to the entire heliosphere and control direction over very long time periods. But that's so back of the napkin I doubt it's actually feasible.
IIRC, at martian surface temperature, hydrogen atoms have escape velocity. That goes a long way to explaining why there's no water on Mars: there's lots of Oxygen, but most of the hydrogen has fled.
Wish someone more knowledgable about this kind of tech comment on this.
Apparently the design of the JWST is sufficient to reach temperatures as low as 37K on the cold side passively — below the superconducting limit for some materials. They're additionally using a cryocooler to take the temp down to below 7K for one specific instrument.
What kind of event could cause the loss of a planet's magnetic field?
Planetary magnetic fields require a liquid ferrous mantle or core. As Mars cooled, its liquid ferrous material solidified, after which its magnetic field disappeared. The same thing will eventually happen here, and the reason our field still exists is because Earth is a larger planet than Mars, requiring more time to cool down.
More details here: http://arachnoid.com/restoring_mars
Also, the extant atmosphere of Mars is a big advantage. It's not much but it helps at lot relative to vacuum with soaking up heat, letting you synthesize oxygen, etc. And while Mars doesn't have much free hydrogen it has a lot more than the Moon does.
Oh, and then there's daylight. A day on Mars is about a day on the Earth. A day on the Moon is a month. So you've got to have lots and lots of batteries if you're going to last out a lunar night. On Mars you just need a bit more mass of batteries than you have of solar panels.
And there's more gravity on Mars which might be important. We know what 1G does to the body and we know what 0G does to the body but nobody knows if there's a difference between the .4G you get on Mars and the .15G you get on the Moon.
And last but not least, the lower gravity on the moon (according to wikipedia) makes space elevators possible even with current technologies. As those would make space travel a lot easier, thats a huge argument to colonize the moon first.
And yes, L1 is unstable. But the lower bound on how little fuel you have to spend staying at the Mars-Sun L1 is much, much smaller than the Moon-Sun L1. I'd guess 10 m/s of delta-v every year for the Mars/Sun one and 10,000 m/s every year for the Moon/Sun.
Mars is substantially easier to establish a long-term operation on than the moon since you can create many of the materials you need onsite.
The atmosphere on Mars is actually pretty nice at an altitude of negative a couple kilometers, which doesn't exist naturally but we're quite talented at building horizontal tunnels that long so pointing downward can't be that hard.
If you need raw material, robots that never leave the mine don't have scalability problems that human deep mines have and on mars liquid water would be a valuable commodity and robots don't mind water anyway, and solar powered robots can be left alone to generate iron ingots for construction, and for environmental reasons there's no reason to make 100 shallow pits when one deep mine produces just as much and is valuable real estate after digging is complete.
On the earth you can't point a large TBM downward because it'll flood or overheat in just a couple miles or less, but on mars it might be quite useful.
The problem with moholes is eventually you end up with the submarine problem where no matter how tough your metal hole liner is in an abstract sense, it will collapse under rock pressures. So you can't bore a hole clean thru a planet, however interesting that idea sounds.
(edited to add, I looked up data more recent than KSRs old book series, looks like bare rock mines are only possible on mars due to rock blowing out to a depth of 10 KM (better than earth, lower gravity), of course the sky's the limit with steel liners. And at a mere 5 deg/km temp increase on mars, the temp will be cold but more habitable than the surface)
NASA might have to think about how to counter such threats, possibly from a future and more hostile Earth civilization.
"While it might seem like something out of science fiction, it doesn't hurt to crunch the numbers!"
Now we need those numbers.
From a terraforming standpoint, a viable, long-term magnetosphere is necessary in the medium and long term. In the short term, humans would be stuck in shielded suits and indoors, both to protect from radiation and to ensure a breathable atmosphere.
Edit: Titan is a moon of Saturn. Oops.
Saturn, which Titan orbits, is 9.6 times farther, and receives 1% of the sunlight that Earth receives.
Mars is much better at 1.5 times farther, and receiving 44% of the sunlight that Earth does.
Also, Titan averages -179C compared to Mars' range from -125C up to 20C.
There's also this very short pdf release which has no interesting detail. http://www.hou.usra.edu/meetings/V2050/pdf/8250.pdf
E.g. could we partially cancel out earth's magnetic field in order to control atmosphere loss and thereby control the greenhouse gas effect?
That's officially called a "deflector", anyone who's seen Star Trek knows.
A variation put into the Earth-Sun L1 and used to direct focused steams of solar particles onto an earthward target....
You jest, but look at the difficulty of countries agreeing on carbon pricing. Which is a similar prisoners dilemma
This is still infeasible now, but it seems much easier than terraforming. With robotic labor and automation, it may not even be that expensive.
I call that bad.
This is the difference between weather and climate. I can't tell you what will be precise weather in one year, but I can tell you that January will be probably cold.