Do the Sun's or Earth's magnetic field reverse? (Intermediate)

I heard that the polarity tested in the sun shows that a change of polarity is taking place and the same thing is happening on earth. Do you have any information about that and if so any idea about consequences?

The sun goes through an 11-year sunspot cycle, where every 11 years, the number of sunspots on the sun decreases to a minimum, rises to a maximum, then reaches a minimum again. In reality, though, the cycle is really 22 years long, because at each minimum, the polarity of the sunspots reverses. You see, sunspots usually come in pairs, with one spot having north magnetic polarity, and the other having south polarity. In any single cycle, for the north or south hemisphere of the sun, the north-polarity spot is either on the west or the east of the south-polarity spot. In the next cycle, those polarities reverse. With the same method that is used to determine sunspot polarity, scientists can also determine the global polarity of the Sun itself by looking at the part of the heliosphere above the magnetic poles. This has demonstrated that the entire solar magnetic field is reversing along with the polarity of the sunspots.

We also know that the global magnetic field of the Earth has reversed polarity many times in the past. We know this because when undersea volcanoes erupt at sea floor spreading centers, the iron minerals (primarily magnetite) in the lava crystallize along the Earth's magnetic field lines. As the sea floor spreads out away from the rift zones, we get an excellent history of the Earth's magnetic field, as if reading a tape recorder of polarities. The sea floor closest to the rift is youngest, and that farthest from the rift is oldest. If you look at the crystal alignments, you see bands of crystals, parallel with the rift all pointing north, then suddenly all pointing south, then north again, etc. This is clear evidence that the Earth's magnetic field reverses regularly.

Consequences of all this, I'm not sure. No one really understands why the Earth's field does this. We do know that the field is generated by convecting liquid iron and nickel deep in the outer core of the Earth. This is so deep in fact, that even for major upheavals down there, we would be unlikely to tell the difference, except by careful measurement of earthquakes and, of course, the magnetic field reversal.


This page was last updated on June 27, 2015.

About the Author

Kristine Spekkens

Kristine Spekkens

Kristine studies the dynamics of galaxies and what they can teach us about dark matter in the universe. She got her Ph.D from Cornell in August 2005, was a Jansky post-doctoral fellow at Rutgers University from 2005-2008, and is now a faculty member at the Royal Military College of Canada and at Queen's University.

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