Some of the pet disasters that science-fiction movies court involve the crew losing their minds. Or spacewalks going awry. Or starships blowing up. Or on-board computers turning nefarious. Then, of course, there’s the perennial favorite of alien attacks.
None of these events touch on an invisible, but deadly, peril that men and women encounter each time they leave Earth. In fact, overcoming it one of the biggest obstacles to venturing out far from home. The cosmos isn’t a benign, inky void, dotted with twinkling stars, translucent rocks and strikingly beautiful gaseous balls with glittering Hula-hoops around them.
It’s also bristling with harmful radiation that’s lethal because of its penetrative power. It packs so much energy that it can rip through a spacecraft’s hull, pierce a spacesuit, puncture the skin, penetrate a cell and tear apart a strand of DNA, irreparably damaging it.
“Galactic cosmic rays” are one source of such radiation. The bare nuclei of atoms of nearly every element, ranging in size anywhere between a single proton (hydrogen) and a platoon of 92 protons and 143 neutrons (uranium), they originate in deep space, outside the solar system.
Within the solar system, the Sun is a wellspring of several emissions.
At its default setting, it gives off a gaseous stream of charged particles that’s present everywhere in the heliosphere. This is known as “solar wind.”
From time to time, that’s compounded by explosions on the Sun called “flares,” which are giant bursts of X-ray that shoot up from its non-solid surface—the photosphere—and travel at the speed of light in all directions.
The halo surrounding the Sun—the corona—also belches huge clouds of plasma—a soup of positively charged protons and negatively-charged electrons—called “coronal mass ejections.”
A watered-down version of this radiation mix reaches us all the time, but it’s mostly blocked out by Earth’s robust magnetic bubble. On top of that, the layers of our atmosphere act as a thick concrete shell, shielding us from the lethal billows.
But once outside this protective cocoon, humans will be exposed to its full fury. A radiation-proof vessel hasn’t been built yet.
According to the U.S. Nuclear Regulatory Commission, on average, a U.S. resident is exposed to an annual doze of 6.2 millisieverts of radiation, which comes from all around us: from the radon in the air we breathe to the bananas we eat.
But that’s nowhere near as pernicious as what we’re exposed to in space. During a 360-day round-trip to Mars, astronauts will be exposed to 100 times the terrestrial dose, about 660 millisieverts. On their excursions on Martian soil, they’ll be bombarded by another 11 millisieverts per year.