One of the many things used to argue against manned space flight beyond low Earth orbit is solar radiation. In low orbit astronauts are protected by the Earth’s magnetosphere which is what enables life to exist on Earth.
The magnetosphere produced by the Earth’s core cause the charged particles of the solar wind to spiral away from the Earth’s atmosphere. It is what produces the borealis at the north and south poles.
The idea of using magnetic fields as shields against the solar wind were dropped early in the space age because it was thought that we could not produce a field strong enough to deflect the sun’s radiation.
New discoveries have shown that a small magnetic field will produce a larger shielding effect than first thought. Scientists in the UK have shown that a small magnetic field is reinforced by the very charged particles it is trying to deflect. This discovery could remove one of the obstacles to a manned Mars mission.
A full explanation can be read here: