writes "One curious feature on the Moon's surface are “lunar swirls”, wisp-like regions that are whiter than surrounding areas and that, until recently, astronomers could not explain. But one team of physicists recently showed that these areas are protected by weak magnetic fields that deflect high energy particles from the Sun and so prevent the darkening effect this radiation has. The problem they had to solve was how a weak field could offer so much protection, when numerous studies of long duration spaceflight have shown that only very powerful fields can act like radiation shields. The team now says that these previous studies have failed to take into account an important factor: the low density plasma that exists in space. It turns out that this plasma is swept up by a weak magnetic field moving through space, creating a layer of higher density plasma. That's important because the separation of charge within this layer creates an electric field. And it is this field that deflects the high energy particles from the Sun. That explains the lunar swirls but it also suggests that the same effect could be exploited to protect astronauts on long duration missions to the moon, to nearby asteroids and beyond. This team has now produced the first study of such a shield and how it might work. Their shield would use superconducting coils to create a relatively weak field only when it is needed, during solar storms, for example. And it would create a plasma by pumping xenon into the vacuum around the vehicle, where it would be ionised by UV light. The entire device would weigh around 1.5 tonnes and use about 20 KW of power. That's probably more than mission planners could currently accommodate but it is significantly less than the science fiction-type power requirements of previous designs. And who knows what other tricks of plasma physics engineers might be able to exploit to refine this design. All of a sudden, long duration space flight looks a little more feasible."