Science Questions

Do other planets switch magnetic poles?

Sat, 25th May 2013

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Andy Rendle asked:



As it seems that we are soon in for a magnetic polar switch, does this happen on other planets in our solar system? Does it happen to a star?




Andy Rendle



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Don't know if we are?
What makes you think we are, and what would 'soon' be? If you by it mean that the magnetic field varies, then I agree, but if you by it mean that South will become North, then that's news to me. Even if it would happen the idea behind it, as far as I know, is that it then would be a gradual change, and that we at no time will find earths magnetic field to disappear. yor_on, Thu, 2nd May 2013

Current theories suggest that the magnetic field of the Earth and the Sun originate in a turbulent conductive layer - for Earth this is molten nickel/iron in the outer core; for the Sun this turbulent layer is composed of hot plasma. Magnetic fields with reversals have been reproduced in the laboratory and computer simulations.

It is also possible to have a "fossil" magnetic field "frozen" into magnetic minerals in a solid planet. However, these are unlikely to spontaneously reverse. On this basis, bodies in our solar system which are entirely solid, like the asteroids, planetoids, most moons and the smaller planets like Mercury, Venus & Mars should not have an active magnetic field.

The atmosphere of the gas giants like Jupiter and Saturn is made of non-conducting gas, so this can't generate a magnetic field. However, it is thought that enormous pressures at the center of Jupiter could form a conductive metallic form of Hydrogen. If part of this conductive core were liquid, it may be able to create an oscillating magnetic field.

But we have not had long-term satellites orbiting all these planets long enough to tell if the magnetic field reverses.

Reversing magnetic fields on our Sun happens about every 22 years. The sunspot cycle peaks about every 11 years, and the number of sunspots reflects the intensity of the Sun's magnetic field. The field reaches a maximum in one direction, declines to a small value and then gets stronger in the opposite direction. The sunspots are at a maximum when the magnetic field is at its minimum strength. See

We know most about the Sun because it is closer, but it is possible to measure the intensity of a distant star's magnetic field by the effect it has on splitting the emission lines in the star's spectrum. It is also possible to detect sunspot activity on some stars (the Kepler telescope is good at monitoring sunspots). These factors suggest that other stars also have oscillating magnetic fields. See

When a neutron star forms, the star's original magnetic field is compressed into a small volume with an incredibly strong magnetic field trapped in superconducting "neutronium". The existence of "starquakes" suggests that at least the crust of neutron stars is pretty solid, suggesting that perhaps this magnetic field is now "frozen"?

As for the Earth's magnetic field reversing, we see continual changes in the strength of Earth's magnetic field. It is thought that the magnetic field would not disappear entirely, but it would become much weaker at the surface, perhaps appearing in a "quadrupole" configuration with two "North" magnetic poles and two "South" poles, none of which would be near the Geographical North or South spin-axis poles! evan_au, Thu, 2nd May 2013

Evan, you keep impressing me with your facts :) yor_on, Thu, 2nd May 2013

I find that Wikipedia has a pretty accessible explanation of most topics - provided you know what keywords to search for... evan_au, Fri, 3rd May 2013

We also know that the sunspot cycle of the sun was very different shortly after the sunspots were discovered about 400 years ago during the period know as the Maunder Minimum

Unfortunately we have no good way to tell for sure what the solar magnetic field was like during that period.  We know that the sun's magnetic field currently has been reversing about every 11 years (not 22), but we can't be sure that it always does that.  A full cycle, returning to the previous state would be 22 years.

I have wondered if Earth's weakening magnetic field is somehow related to the fluctuations in the sun's magnetic field, and it may stabilize in the future.  As others mentioned, a "flip" likely won't happen for at least decades, or perhaps centuries into the future, and there is no way to know if will happen at all.  CliffordK, Sat, 4th May 2013

Someone still need to put them together Evan, there are a lot of facts out there, but getting them comprehensive and joining them takes time, and understanding. Otherwise I definitely agree, I think Internet is the biggest invention since the wheel, having the potential to revolutionize our understanding of each other, as well as educate ourselves in our own time.

hopefully so :)
yor_on, Mon, 6th May 2013

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