A Descendant of Ernst Stavros Blofeld, famed nemesis of super-spy James Bond, was shooting pool one day with some friends when he uttered the most terrifying phrase in human history... "Here, hold my beer."
What happened next stunned half a galaxy — which was fine with Amaranthos Ophiouchos Blofeld, who loves to be the center of attention. You see, what he did was hold the Capella star system1 ransom! What he didn't count on was the reigning oligarch, His Excellency, President for Life, Field Marshal and Doctor Rhamadahaman, Lord of All the Beasts of the Earth and Fishes of the Seas and Conqueror of the Aldeberan Empire and Cygnus Minor in Particular,2 calling his bluff. Nobody calls a Blofeld's bluff!
You see, a week before he'd been reading this historical article from Space.com where he learned...
The reversals take place when iron molecules in Earth's spinning outer core start going in the opposite direction as other iron molecules around them. As their numbers grow, these molecules offset the magnetic field in Earth's core. (If this were to happen today, it would render compasses useless as the needle would swing from pointing towards the north pole to pointing to the south.)
During this process, Earth's magnetic field, which protects the planet from hot sun particles and solar radiation, becomes weaker.
And that gave him an idea, what if he could play enough merry havoc with the molten iron in the core of every planet in the Capella star system that had a molten iron core just long enough, oh, maybe a couple of hours or so, to let the amazing solar maelstrom caused by four stars to gently barbecue the snot out of each planet?
You see, what's happening here is that a planet's magnetosphere is created by the planetary liquid core, and it affects the planetary liquid core. In the case of Earth (which we will egregiously extend to all planets enjoying a liquid core), the inner core and outer core spin in different directions.
"Previously, there have been these two independent observations, and there has not been a link between them," study co-author Philip Livermore, of the University of Leeds, told LiveScience's OurAmazingPlanet. "We argue that the magnetic field itself is pushing on the outer core, and there is an equal and opposite push on the inner core." (Source)
What this means is that all one need to do to get the poles to flip (or, better yet, to almost flip) is to change the rotational speed of one of the cores (inner or outer) such that the compounded effect from the magnetosphere would be to create a metastable condition.3 In true Hollywood fashion, what we're trying to do is get the engine that creates the magnetosphere to stall... just for the proverbial second!
Amaranthos is convinced that one way to do this (one not previously considered by the greater scientific community)4 would be to change the rotational speed of one of the two cores. It doesn't matter which one, and it doesn't matter how much so long that it's enough to destabilize the balance between the two core rotations and the magnetosphere. Frankly, if you noted the progression of one of the poles, you probably could work out where to apply pressure to get it to move just a little bit more....
From a very simplistic point of view, it's like changing the gearing between a motor, a flywheel, and the load connected to the flywheel. If you rapidly and dramatically change the balance of energy, the system attempts to compensate — and the result can be spectacularly violent.
How did Amaranthos plan to do this? In true Blofeld style! He realized that he could sneak the millions of nuclear weapons needed to superheat the outer core of each planet (because hot things move faster, right? And it's so much simpler to heat things up...) into place without attracting anywhere near the attention that such an action would normally deserve. All he had to do was
[Redacted for national security reasons] and when the Prefect of Greffetacle heard about it, he actually laughed out loud!
So, when old Rhamadahaman sent Amaranthos a text and called him an overrated blowhard good for nothing more than the entertainment of his troops... well, naturally, Amaranthos pushed the button.
And when the magnetosphere collapsed on all those planets, they were snuffed out, cooked to a crisp, and left irradiated for generations. As Blofeld said when he reclaimed his beer, "I pity the fool who tries to mine on one of those planets!"
1 The planets are there. I'm sure of it. You just need to look harder! Try squinting....
2 With all due respect to Idi Amin Dada Oumee, who never let common sense stand in the way of first-class title mongering.
3 A fancy way of saying, "a moment where the darn planet doesn't really know what it wants to do."
4 Did he forget to add "scientific god among men" to his title? I'm sure I left him a note to add it. I'll get right on that.