This past April, business traveler Tom Stuker became the world’s most frequent flyer, logging 18,000,000 miles of air travel on United Airlines over the last 14 years.
That’s a lot of time up in the air. If Stuker’s traveling behaviors are typical of other business flyers, he may have eaten 6,500 inflight meals, drunk 5,250 alcoholic beverages, watched thousands of inflight movies and made around 10,000 visits to airplane toilets.
He would also have accumulated a radiation dose equivalent to about 1,000 chest x-rays. But what kind of health risk does all that radiation actually pose?
Cosmic rays coming at you
You might guess that a frequent flyer’s radiation dose is coming from the airport security checkpoints, with their whole-body scanners and baggage x-ray machines, but you’d be wrong. The radiation doses to passengers from these security procedures are trivial.
The major source of radiation exposure from air travel comes from the flight itself. This is because at high altitude the air gets thinner. The farther you go from the Earth’s surface, the fewer molecules of gas there are per volume of space. Thinner air thus means fewer molecules to deflect incoming cosmic rays – radiation from outer space. With less atmospheric shielding, there is more exposure to radiation.
The most extreme situation is for astronauts who travel entirely outside of the Earth’s atmosphere and enjoy none of its protective shielding. Consequently, they receive high radiation doses. In fact, it is the accumulation of radiation dose that is the limiting factor for the maximum length of manned space flights. Too long in space and astronauts risk cataracts, cancer and potential heart ailments when they get back home.
Indeed, it’s the radiation dose problem that is a major spoiler for Elon Musk’s goal of inhabiting Mars. An extended stay on Mars, with its extremely thin atmosphere, would be lethal due to the high radiation doses, notwithstanding Matt Damon’s successful Mars colonization in the movie “The Martian.”