actually it's not uncommon.  there are structures inside the mantle and core of spiraling liquid metals and silicas that create the magnetic effect, of course they break from time to time and the poles can become aligned at different angles, or indeed, create numerous fields not just one north one south. the tendancy appears to be they align with the axis of rotation either n to s or s to n. we've never had the opportunity to measure or witness a flipping yet.
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