Magnetosphere

The Magnetosphere is the region of space surrounding a celestial object that is affected by the objects magnetic field.

Origin

The Earth's magnetosphere is thought to be generated by its rotating iron core. This is commonly referred to as a Dynamo. In order for a planetary core to act as as a dynamo it must contain a rotating liquid metal and there must be convection. Current theory is that the core of Mars has cooled enough to solidify or become plastic, but seismic investigations will be required to confirm or disprove this conclusion.

Apaperntly this is what the esteemed Willis was talkin' 'bout.