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Continuing along my oft-contineud series of questions relating to terraforming, I return to an idea of giving Mars a magnetic field which I had hitherto dismissed. The idea is that a huge superconducting ring or rings, (basically a magnetised hoop) is built around a planet’s equator, where, once magnetised, it produces a magnetic field which the planet is presumably lacking. Presumably the ring is buried at least a kilometre below the surface, in order to prevent it having to cross oceans/forests/have bridges built over it.

However, finding no particular specifics regarding this process, I would like to ask: would the hoop require an external source of power? Or would the magnetic field it produce be permanent? And am I right in assuming this ring would be buried below ground?

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  • $\begingroup$ Keeping superconductors superconducting usually requires deep refrigeration, which consumes a lot of power. $\endgroup$
    – AlexP
    Dec 30, 2022 at 20:09

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No, the field generator would not be underground

It would be positioned at the L1 point of Mars.

magnetic shield diagram

According to NASA Planetary Science Division director Jim Green, a powerful magnetic dipole positioned at the Mars L1 Lagrange Point could potentially deflect the solar wind like a natural magnetic field. The L1 Lagrange Point is a location of gravitational equilibrium that ensures the structure remains between Mars and the sun.

The satellite may use an array of solar panels to power the whole affair. It's not a permanent solution, as the satellite/station requires continual upkeep, but if you're serious about terraforming, throwing a fraction of a fraction of your budget at its maintenance should no problem whatsoever.

As a side note, an artificial magnetosphere isn't strictly necessary to terraform Mars (they're waaay overrated), but being so cheap to build compared to the scale of the operation you may as well do it anyway. Earth loses something like a couple cubic meters of air every second to space, but life (specifically photosynthetic life in the ocean) and chemically-reducing natural processes replenish it far in excess of what's lost to space (if memory serves, plankton produce something like 300 billion tonnes of oxygen annually). If you're capable of raising the pressure and atmospheric content of a near-airless world in mere centuries, topping off what meager amounts escape to space is nothing.

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  • $\begingroup$ Ignoring the effect on the atmosphere, would an artificial magnetosphere be useful in terms of radiation protection? Humans on the Martian surface would like to know. $\endgroup$
    – Cadence
    Dec 30, 2022 at 22:27
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    $\begingroup$ @Cadence Well, for one thing, magnetic fields do nothing to stop UV, and EM in general. That's the atmosphere's job. Solar ions like alpha particles would be stopped by the atmosphere, too. The magnetosphere does very little to protect people on the ground. $\endgroup$
    – BMF
    Dec 30, 2022 at 22:29
  • $\begingroup$ It is not so much atmospheric loss I am worried about here; solar wind removes water to, and as far as I know in a really short space of time. This is why Mars has lost its oceans; once its core solidified, the magnetic field collapsed and the solar wind stripped them away. $\endgroup$
    – user98816
    Dec 31, 2022 at 10:43
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    $\begingroup$ @user98816 water is lost by the same mechanisms as atmosphere is lost, specifically hydrodynamic escape where numerous collisions with lighter ions like hydrogen can push heavier ions like oxygen and disassociated water out of the atmosphere. $\endgroup$
    – BMF
    Dec 31, 2022 at 18:07
  • $\begingroup$ It's dependent on the rate of thermally-driven escape of lighter ions, which could be less severe at Mars given it's farther from the Sun than Earth, but Mars is less massive than Earth. In short, water loss shouldn't be that big an issue, you should be able to replace it far in excess of what's lost if you can create oceans in the first place. You're certainly not going to lose your new oceans in a matter of centuries. Maybe millions of years. Also keep in mind a strong magnetic field isn't going to stop this effect, only slow it slightly. It's a product of having a "hot" atmosphere. $\endgroup$
    – BMF
    Dec 31, 2022 at 18:14
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Alternative

A magnetic umbrella over mars. Although it might be possible to build a ring of magnets on the surface that splashes radiation around the planet like earths magnetosphere, it's mighty inefficient.

If you're not concerned about cosmic rays because this terraformed mars would likely have its own ozone layer, then a superconducting magnetic umbrella in the Lagrange point between the sun and mars would be ideal.

The hoop of high temperature superconducting coils (likely YBCO or some newer material by then) would likely be powered by solar or by that time, fusion energy facilities.

It would only need to act as a literal umbrella and push the solar wind off to both sides, and the magnet doesn't even need to be that big. As you go farther away from mars, the smaller of a magnet you would need, as the 'shadow' you are creating gets bigger the farther away you measure it from.

A magnet a few tens of teslas or less could do the trick, and you'd be shielded indefinitely (as long as the machine runs and can be maintained). A bonus is that you'd likely have aurora boreali, although they'd be invisible as the sun would sadly block it out.

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