Shields up! Force fields could protect Mars missions - space - 28 July 2010 - New Scientist

Shields up! Force fields could protect Mars missions: "Some parts of the solar wind shift more easily than others. The positively charged protons have nearly 2000 times the mass of the negatively charged electrons, so the latter are much more easily deflected. The electrons stay at the surface of the magnetic bubble, while the positive charges penetrate further in.

This separation of positive and negative charges generates intense electric fields up to a million times stronger than the magnetic fields that created them. Subsequent solar wind particles hit these electric fields and are strongly deflected. The result is a shielding effect far more powerful than the magnetic field alone might be expected to provide."