Today has been an interesting day to be a physicist because of the solar storm. I've been following links on Twitter all day to information about the coronal mass ejection and induced ground current and the promise of spectacular aurora tonight. If you live up North go look! Nothing to see here in the Deep South.
Dr. Ian O'Neill posted a story this afternoon about airlines diverting their polar routes. I asked him on Twitter if he found it interesting that the airline says the change is to reduce the risk they'll lose radio contact with the plane and don't mention the increased radiation to the passengers and crew. I sort of remember learning that it was the bad kind of radiation back in college, but they could have changed their mind since then. He sent me back this link to a great NOAA chart. Here's the relevant excerpt.
The first number column is Flux level of greater than or equal to 10 MeV particles (ions)*, the second is Number of events when flux level was met (number of storm days**) The *** note says *** High energy particle measurements (greater than 100 MeV) are a better indicator of radiation risk to passenger and crews. Pregnant women are particularly susceptible.
These units are confusing. Basically it's saying this measurement isn't really that good for judging harm to humans. They're measuring the less energetic particles or slower moving protons. Flux is just a complicated way of counting them. Dr. O'Neill confirmed my hunch that basically it's the protons that get you. The faster ones are worse and they aren't calculating a flux level for those, so it's hard to say how bad it really would be to fly in a plane over the North Pole right now. The radio interference is an easy call though. Go the long way.
A solar storm has many parts. It starts with a solar flare. The magnetic field lines in the corona of the sun sometimes get too close together and they have to rearrange themselves. (Like in Ghostbusters, when it comes to magnetism you can't cross the streams). This sudden rearrangement is a solar flare. First it shoots out x-rays at the speed of light. This is the stuff that interferes with the radio transmissions. If the spot on the sun is aimed at the earth those x-rays get here in about 8 minutes. (Remember not all the stuff the happens on the sun is headed our way. Most of it misses.) Next there is a blast of subatomic particles (protons, electrons, and heavy nuclei - sets of protons and neutrons with no electrons, typically it's the middle out of a Helium atom, also called an alpha particle) which get here later. That speed is not a constant, it can vary by the intensity of the solar flare. That's why this NOAA chart has the different ratings. It's like Joerg Sprave on the Slingshot Channel shooting different marbles into ballistic gel to see how deep they penetrate. It's the penetrating power of a particle that is a health concern. Think of a proton like a marble and an alpha particle (that heavy nuclei) like the rock. The marble goes deeper into the gel.
After the actual solar flare there can be another phenomenon, a coronal mass ejection. The corona is a plasma -- all the particles are free, not bound up in atoms with a set of protons, neutrons, and electrons. It's electrically neutral, so there are an even number to make atoms, but they aren't all arranged as hydrogen, helium, and so on. So when the magnetism of the corona rearranges itself (a solar flare) and kicks out a portion of the corona, it sends more subatomic particles flying. In the case of the coronal mass ejection yesterday they were going about 5 million miles per hour. That's slower than the second part of the solar flare, but still darn fast. It hit the atmosphere at 10 am my time.
So why is being bombarded by high energy protons especially bad for pregnant women? My understanding is that if a proton collides with the the exact right spot it could could cause a mutation in DNA. In a fetus the cells are rapidly replicating themselves, so it can magnify the damage. The faster the proton is going the more energy it has to do damage when it collides with something. (Subatomic particles are tiny. They can go right through you and come out the other side cleanly, like shooting a pellet gun through a chain link fence. Neutrons are notorious for doing this. Protons aren't quite as good at it. They have to be going pretty fast to get through your skin. Those heavy nuclei, they can't get through a piece of paper going their normal speed.) Of course the odds are extremely remote that a proton shot out of the sun would skitter along the magnetic field of the Earth to the hole at the North Pole, go through the outer layers of an airplane, through a woman's skin and tissue to collide precisely with an atom in her fetus and break the DNA. And then there is the remoteness that the resulting break would turn into a nasty tumor one day. But if you increase the number of particles and their speed (more intense radiation) then it's pretty obvious that the risk is increased. The same thing could happen in an adult and could cause them to get cancer, but fetuses are creating new cells much faster and could duplicate the damage rapidly. In 2006 scientists at Brookhaven National Labs announced that proton radiation is more dangerous than previously thought. I read this article after I wrote this paragraph, but it looks like I got it right. If you want to know more about the biological damage from protons and how they measured it, click that link. Here's another good one from 2009 describing an experiment to expose a faux astronaut to a beam of accelerated protons to simulate a solar flare.
I often have a hard time understanding the language of risk in medicine, but this one I get. I agree with O'Neill that a plane ride to view the aurora would be wonderful. I would totally do that. I don't care if I get irradiated. But if I was a pregnant woman? No way. Send me a link to the YouTube video after you land.
This post needs multimedia. Here's the slingshot video I mentioned.
Update: Here's a new article by O'Neill that gives great detail about aurora and the coronal mass ejection factors that affect it.
This article in IEEE Spectrum is really good too. Explains induced current in pipelines and other conductors and discusses some historical solar events.