Solar Flares and Air Travel
What are solar flares? Do they affect radiation dose
when I fly? Can cosmic radiation during plane flights hurt me? Can
radiation from solar flares hurt the fetus of a pregnant
woman?
- The sun produces energy by fusing hydrogen in its core. This
reaction is very close to what happens in a hydrogen bomb, but on
a hugely larger scale. The amount of energy produced by hydrogen
fusion in the sun’s core heats the sun and drives solar activity
as it makes its way to the sun’s surface and into space.
- The surface of the sun is much cooler than the core, but it is
still tremendously hot by our standards—about 6,000 degrees
centigrade. Partly because of this high temperature, gas from the
sun is continually driven off into space; we call this the solar
wind. The solar wind is simply protons (the nuclei of hydrogen
atoms), neutrons, electrons, and alpha particles (the nuclei of
helium atoms)—the same materials the sun is made of—that travel
through space at velocities of hundreds of kilometers per second,
and some of this solar wind reaches the Earth as one component of
cosmic radiation (the rest of cosmic radiation comes from outside
the solar system and is called galactic cosmic rays, or GCRs). The
Earth’s magnetic field helps to shield us from much of the sun’s
radiation, funneling the electrons, protons, and alpha particle
into radiation belts that surround our planet instead of letting
them reach the ground. And our atmosphere provides fairly
substantial shielding too against the cosmic rays that penetrate
the magnetic field.
- In addition to hot gas, the sun’s surface is also penetrated
by magnetic fields, as is the Earth’s surface (although the
Earth’s magnetic field is not nearly as strong). In places, the
solar magnetic field is stronger than in others and, in some of
these places, the magnetic field lines of force can become
twisted, which is a way of storing energy. Think of a rubber
band-driven airplane; we can hold the airplane steady while
twisting a rubber band around and around. As we twist the rubber
band, we are storing energy, and when we let go of the propeller,
that stored energy causes the propeller to turn quickly enough to
let the plane take off. In an analogous manner, the twisted solar
magnetic fields store energy and, when that energy is released, it
sprays huge amounts of hot gas into space. This is a solar flare.
- The particles emitted during a solar flare are high-energy
hydrogen and helium atoms that have had all of their electrons
removed. But alpha radiation is high-energy helium nuclei and
hydrogen nuclei are simply protons. Both of these are forms of
radiation, as are the electrons (beta radiation) and neutrons
found within the gas. In other words, a solar flare is a huge
emission of radiation from the sun, and if it’s aimed at the
Earth, we will experience higher levels of radiation because of
this.
- Not all of the radiation emitted by a solar flare will reach
the earth—some will be dissipated by the interplanetary magnetic
field, some will simply miss the Earth entirely, some will be
deflected or captured by the Earth’s magnetic field, and some will
be absorbed by our atmosphere. Solar flares that can be measured
at the Earth’s surface are very rare, but it is more common to be
able to measure solar flares at the altitudes at which commercial
aircraft fly.
- Even given that, the increase in radiation levels to aircraft
crew and passengers is not very large. For example, during normal
solar weather, one can expect to receive a radiation dose of about
71 microsieverts (about 7.1 mrem) flying from the eastern United
States to Australia and about 85 microsieverts flying to Japan
(the Japanese flight is farther north, where the Earth’s magnetic
field is weaker). This level of radiation dose is about the same
as a week’s worth of natural background radiation. Studies have
not shown that this level causes any harm to those exposed.
- According to the National Oceanographic and Atmospheric
Administration (NOAA), radiation dose from solar flares can reach
as high as 200 microsieverts per hour (20 mrem/hr) for up to a few
hours at commercial aircraft altitudes. This would give a
radiation dose of up to 400-600 microsieverts (40-60 mrem) during
a two-to-three-hour solar flare. Although this is a higher
radiation dose than is normally experienced, such solar flares are
expected to occur only a few times during the 11-year solar cycle
and the great majority of passengers simply won’t be in the air
when one occurs. Even for those passengers who are exposed to this
level of radiation, the expected effects still are not
significant—this level of radiation exposure is similar to
receiving an x ray and is far less than what you get in a CT scan.
- You can find more information about radiation from solar and
galactic cosmic rays at the NOAA Web site and
the FAA Web site has a cosmic
radiation dose calculator that can be used to calculate
radiation dose from routine flights.
- So, even during large solar flares, passengers will not
receive a radiation dose to be concerned about, but pregnant women
worry about the effects on their children. Studies of airline
flight attendants show that even those who make a career of flying
do not have any demonstrated ill effects from their occupational
radiation exposure, and studies of pregnant women exposed to
medical radiation (as well as pregnant women exposed at Hiroshima
and Nagasaki) do not show that there are dangers to the developing
fetus from radiation doses far higher than what anyone will be
exposed to on an airplane. In other words, a fetus simply will not
receive enough radiation during flight (even during a large solar
flare), even during the most sensitive times of fetal development,
to cause any problems.
- There is a lot of information on this matter on the Health
Physics Society (HPS) Web site and this information comes from
medical doctors as well as from radiation safety professionals. A
Web site unrelated to the HPS with similar information is the Baby
Center Web site.
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