Radiation and Mars

Even though I'm on sabbatical and focusing on my own research (more on this later), I still read and keep up with developments in physics and physics teaching. One of my interests is radiation and its effects on humans, and how it might block our plans to colonize the solar system (or at least send humans to Mars). Mars One is an organization that is planning to send humans to Mars in the foreseeable future, but first they want to send an unmanned mission in 2018 (and well they should). A colleague of mine at Embry-Riddle Aeronautical University is submitting a proposal for an experiment that will measure the effects of radiation on flies during the trip to Mars. I believe that this is fundamentally the one issue (among all the problems that we need to solve in order to live in space) that will effectively stop us from leaving Earth permanently.

While we're on the surface, there are two factors that protect us from the particle radiation (mostly protons and electrons) that bombard the earth constantly from space: the Earth's atmosphere and magnetic field. The magnetic field deflects the charged particles, except near the poles, and the atmosphere effectively absorbs them. However, there are a few that make it through, and these are thought to cause some of the mutations that are responsible for evolution. The ISS is above most of the atmosphere, but still within the protective magnetic shell, so while astronauts have more exposure than humans on Earth, it is unlikely that the radiation (for the short time they are in space) contributed to any subsequent cancer.

Once you are away from the Earth's magnetic field, say above 100,000 km altitude, humans are fully exposed, and there is no current spacecraft who's walls are thick enough to block this radiation. Eugene Parker has a nice Scientific American article "Shielding Space Travelers," in the March 2006 issue, that describes the problem nicely. It is estimated that each year in 'outer space' is responsible for a 10% increase in the risk of cancer, and a 5% increase in the risk of a fatal cancer. A trip to Mars and back would take 3 years minimum, without any stay on the surface. And going further, say to the nearest star - Proxima Centauri - would mean a lifetime. 20 years in space would probably guarantee your death of cancer. Lifetimes would be extremely short. Of course, once on the surface of Mars (which has no significant magnetic field or atmosphere), protective structures could be built. But any humans that permanently lived there would be confined to the interior of these structures. A very different life.

The motivation for these thoughts is a recent article in The Physics Teacher, called "Three Misconceptions About Radiation" by Susanne Neumann from the University of Vienna. Her list is

1. Radiation is artificial
2. Radiation is harmful
3. Radiation is invisible

Everything is radioactive to some degree, even the water we drink, and simply walking around with a Geiger counter proves that. Radiation is not just linked to our advanced technology. Too much radiation can be harmful, but the necessity of radiation for evolution should not be overlooked. While protons and electrons are "invisible," and other radiation, like IR and UV, is also invisible. But light is a form of radiation, and is in fact, just like IR and UV, but with a different wavelength.

So consider this post as my attempt to inform you about radiation, and to motivate you to learn more.