Do the magnetic fields of the planets affect spacecraft during flybys?

Yes, a spacecraft that has a net charge will feel an effect due to the “Lorentz force” while moving through a planet’s magnetic field. (English scientist Oliver Heaviside actually derived the effect in 1889, a few years before Hendrik Lorentz.) The Lorentz force is a non-fundamental force, meaning it’s not in the same class as gravity or the strong nuclear force. According to Lorentz and Heaviside, the charged particle “feels” this force perpendicular to both the magnetic field it is traveling in and the direction it is moving.

Studies have shown that spacecraft surfaces charge differently in shadow and in light. This is because when the Sun’s photons hit the surface, they can launch electrons out of atoms — a consequence of the photoelectric effect, which Albert Einstein discovered more than a century ago (and which he won the Nobel Prize in physics for). The charged spacecraft’s trajectory, in theory, is then deflected as it moves through a planet’s magnetic field. However, for all the probes that have flown by planets over the years, no Lorentz force effects have been detected. We know the negligible effect is there, though, because of the laws of physics.

Some research in recent years suggests that a spacecraft could be artificially charged during flight to high enough levels for the Lorentz force to aid space navigation, which could perhaps eliminate the need for midcourse maneuvers using the craft’s propulsion system.