At some point I saw a design for a machine you could park at the Lagrange point between Mars and the Sun that would collect solar power and spit out a magnetic field strong enough to deflect enough of the solar winds that we wouldn't need to worry about that.

There's probably a way to engineer it such that the spin of the planet is 24h, the core is spun up. We'd also like ~365 day years.

It would stay molten for millions of years.

Not sure if Europa's water would be flung into space, make atmosphere, or make a boiling ocean.