Earth's magnetic field protecting us from deadly radiation - A common misconception

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From time to time, I hear the statement that Earth's magnetic field is important because it protects earth from "deadly" radiation, and that when the magnetic field will reverse, this lethal radiation will be... very bad. One such example is this promo for a NOVA program "magnetic storm". Well, I have news. Nothing really bad will happen to us. This is because we have our atmosphere to shield us! (You know, this thing made out of air). Moreover, those high energy cosmic rays that do penetrate the atmospheres, do so irrespective of Earth's magnetic field. Thus, if anything, I am waiting for the magnetic reversal, as it would imply nicer auroras everywhere on Earth, not just for the eyes of the inuit.

Of course, this claim may sound strange to you, but here is some data which you can check, and verify that I am not bluffing:
  • The typical solar particle energies reach at most several 100's of MeV (million electron volt).
  • High energy cosmic rays (coming from the Milky Way) have energies of 1 GeV and higher.
  • The energies stopped by Earth's magnetic field are typically up to 10 GeV, in equatorial regions. At polar regions, Earth's field can stop only lower energies
  • The atmosphere stops primary cosmic rays with energies lower than 10 GeV.
Clearly then, solar high energy particles are stopped by Earth's magnetic field, but would do so also by the atmosphere if there was no B-field. The same goes for cosmic rays with energies lower than 10 GeV. Some are deflected by the magnetic field, but if it weren't for it, they would have been stopped by the atmosphere. Higher energy cosmic rays are not stopped by the magnetic field, however, nor do they do so by the atmosphere (well, to be accurate, the high energy particles are stopped by the atmosphere but the lower energy particles that they form do reach the ground). In fact, the amount of ionized air we have in the bottom atmosphere is totally governed by the flux of 10 GeV cosmic rays reaching Earth (unless you're really close to the ground and may be affected by Radon). Switching off the magnetic field would not be detrimental as often claimed. Switching off the atmosphere would be a different story though...

One last point. The truth is that there will be a few bad repercussions from a reversal. If you're a satellite engineer, it would cause one big headache since the satellites will be exposed to significantly higher fluxes of low energy solar particles. The same is true if you're an astronaut. The same headache which troubles designers of a Mars expedition would have to be considered also for "mundane" near Earth missions. But who said life is easy, especially for astronauts.


Comments (1)

  • anon

    Sorry for the late post but I'm new to your site. It's a GREAT site.

    Another myth is that radiation makes something radioactive. There are only a few special ways that radiation can make something radioactive (basically neutron activation and high energy physics. High energy cosmic rays are one of those special ways.

    C-14 and a host of other nuclides are created by the interaction of high energy cosmic radiation with the nuclides in our atmosphere. It takes high-MeV or GeV energies to disrupt the nucleus of an atom and cause it to change to a radioactive atom. This cannot happen at lower radiation energies, such as those emitted by radioactive materials.

    A macro-level analogy compares a spitwad shooter to a 30-06 rifle. A spit wad doesn't have enough mass/energy to break the skin. The 30-06 on the other hand...

    Sep 21, 2007