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Premise

One of the many conditions needed to support life (as we know it) is a planet with a surface protected from deadly radiation from a sun or even other sources. In the grand scheme of things, the probability of finding a planet that meets every requirement may be rather slim. That is to say, there is a long list of requirements including things like: is there a moon, distance to sun, metallicity of sun, surface gravity of planet, atmospheric composition, size of planet's core, ect. If the universe is infinite then by the law of large numbers we may be bound to find one eventually. That being said, there is no guarantee that the law of large numbers is going to let you find a suitable planet that is close enough for a reasonable journey duration.

Hypothetically, consider a relatively close planet that met all requirements except for the core of the planet was not large enough or not made of heavy enough elements to generate a magnetosphere capable of shielding the planet from radiation. Then suppose a fairly advanced civilization discovers this planet. They may say to themselves, "this planet is so close", and proceed to make do. If their technology was advanced enough, I suppose they could create their own external magnetosphere. However, I am left wondering, in the absence of overly advanced technology, what is the feasibility for strengthening a planets magnetosphere?

Question: That is in essence the question. Can a planet's magnetosphere be strengthened through artificial means?

Further Clarification

  • the lower tech, the better
  • could be a planet-core oriented solution
  • could be some surface device magneto-amplification solution
  • thresholds in answer would be a plus (what size or ratio is workable, what is beyond salvaging, ect)
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  • $\begingroup$ Yes, easily. Place a suitable magnet at the L1 Lagrangian point. It doesn't need to be huge and can be powered by solar light; such a magnet would be even within current tech level, if a bit on the pricey side. On the other hand, the importance of the terrestrial magnetosphere in protecting life is quite exaggerated; we know that life can survive without a magnetosphere because Earth's magnetic field periodically goes off and then reverses. $\endgroup$ – AlexP Aug 24 '17 at 16:17
  • $\begingroup$ @AlexP Cool idea, have not heard of that before. Wouldn't life at the surface still need a stable magnetosphere in the long run? The magnetosphere here on earth does reverse polarity and flicker on and off as you said, but if it never came back on, wouldn't the prolonged radiation destroy every life form except those in caves and deep oceans? $\endgroup$ – Arash Howaida Aug 24 '17 at 16:25
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    $\begingroup$ The importance of the magnetosphere is not that much in protecting life from "radiation" (whatever meaning you assign to that word), but more in preventing the erosion of the atmosphere by the solar wind. This second effect, while real, takes many millions of years to become noticeable; that's a time scale so vast that nobody will care much. (We don't do plans over such timescales anyway.) A magnetic field cannot do anything against electromagnetic radiation, including gamma radiation; and alpha and beta radiation are (1) much less dangerous and (2) absorbed quite well by the atmosphere. $\endgroup$ – AlexP Aug 24 '17 at 21:05
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This question has been fundamentally answered on Physics.SE. From that site we learn that the energy needed to replace the Earth's magnetic field is:

almost exactly twice the total energy use of the USA per year.

(Although the author, pointing to another answer on Physics.SE, suggests it could be a little lower.) So, could it be done? Yes, given enough energy supply, given large enough conductors, given proper heat dissipation... All things considered, you'd likely need one or two Death Star sized objects to generate the field (maybe one if it was always positioned between planet and star such that the planet's weaker field could facilitate some of the passage of solar winds, etc.).

The first real issue is efficiency. The planet is hugely inefficient, which is why you need a planet to generate the field. Increase efficiency and you decrease the size of the geneator. Efficiency is increased with superconductors (both in material and temperature), better insulators (the thinner they are, the better the field), energy production (solar won't work... trust the electrical engineer), and heat dissipation (probably the single biggest problem).

The second real issue is how close people can be to the center of the magnet. The earth's magnetic field is relatively weak, but massive in scope. We're not affected because we're a long honking way away from the center of the field. At the core of the planet, however, the field would be impressive. An ariticial something would need to handle that impressive field shear near the core of the generator.

Note that we cannot do this with today's technology. Therefore, what the lowest tech could be is a guess.

For the hard math I gladly bow to the experts on Physics.SE.

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Apparently you came to the right planet at the right time ;)

There's a very recent (few months ago) NASA proposal on how to do what you ask, not for a planet orbiting a distant star, but for our friendly neighbor Mars.

It does not do exactly what you ask (creating a magnetic field on Mars itself), but it turns out it would be cheaper (more doable) to put a strong magnet in L1 (Lagrange point 1, which is unstable, but position can be kept with minimal active steering) that can act as "magnetic shield" for the whole planet, allowing it to keep it's atmosphere (deflecting solar wind) and mitigating ionizing radiation (the dangerous one).

If it could be done for Mars I assume it will work also "abroad".

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