I'm conceiving of a world where humans can readily terraform worlds that were once considered "dead" due to the planet's magnetic field being long gone. In such a situation, what could humans do to recreate an artificial magnetic field to protect the planet.
I know it's relatively easy for us to create magnetic fields stronger than that of the earth in a lab, but it's unclear to me how this could be replicated on a planetary scale given an 1/r^2 strength of field over distance
My simplest idea would be a supercooled solenoid running around the planet to generate a magnetic field similar to that on earth. However, I'm not sure how to account for the planet in the center.