What is cosmic radiation?

There are different types of radiation that fall under the general umbrella of cosmic radiation.' But one important distinction to make is that cosmic radiation is fundamentally different than the radiation that most people are familiar with, like x-rays, gamma rays or microwaves. Those are all electromagnetic radiation, which is mass-less. But cosmic radiation is not.

Cosmic radiation is mostly composed of energetic elementslike carbon, oxygen or hydrogenthat are present across space and have had some of their electrons stripped from them. And it's that lack of electrons which makes them radioactivebecause when these elements hit something, they can draw electrons away from whatever they've run into and can break molecular bonds.

And cosmic radiation originates from various places. For example HZE particles, which are the nuclei of heavy elements moving at very high velocities, are largely created when a star explodes in a supernova. And there are other high-energy particles that are ejected from the sun during events called coronal mass ejections.

If this cosmic radiation is found all over the galaxy, how are we protected from it on Earth?

There are two reasons. The first is that we have a natural magnetic field that surrounds our planet. This field deflects a lot of these radiation particles, much like a shield. And the second reason is the Earth's atmosphere. The molecules that make up our atmosphere serve like a protective cloud around the earth. This slows radiation particles down, and forces them to lose energy.

How does this radiation impact the health of astronauts?

It's important to note that astronauts are not safe from these radiation particles inside of a spacecraft or in their spacesuits. Because these particles are incoming at a very high energy and a very high velocity, when they encounter a target they won't bounce off like a Ping-Pong ball, but will go directly through [any protective shielding] and can hit the astronauts inside.

And when these radiation particles enter a person's body, they can disrupt the structure of biological tissues and cells. A main concern is DNA. This radiation can damage the structure of DNA, inducing mutations, and if the body can't properly repair the accumulation of these mutations, we have a concern about cancer. Cancer, while largely a genetic disease, winds up coming from an accumulation of mutations in hotspots for important genes.

But it's no simple issue. There are many types of cancer, and while a given dose of this radiation may leave someone at greater risk for one type of cancer, it might produce no increased risk for another. That's because different tissues respond differently. In fact, while it was feared that leukemia might be one of the main risks of human exposure to cosmic radiation, it does not appear to be; conversely, some data suggests that lung cancer may be.

And because of other factors, like genetics, these cancer risks can also vary from person to person. There are certainly other health concerns toohow this radiation may impact brain function is another story altogether.

So how do you work out the health risks?

Well, clearly you can't just send a person out into space and see how long it takes them to develop cancer. So what we work with at the NASA Space Radiation Laboratory are many experiments with different cell types that we expose to this type of radiation here on Earthand then we use a lot of mathematical manipulations to extrapolate our data into the health risks for people.

But I should note that while our lab has been open for over 11 years, this is time-consuming work. Eleven years sounds like a long time, but it's actually not enough for a lot of data to come in. So it's difficult to put hard numbers on these health risks yet. You're not going to start seeing deleterious health effects after 24 hours; nor can we say that after four years our astronauts would be in perfect health. The health risks of this radiation lies somewhere in the middle, depending on what you're looking at.

Can't we just extrapolate the risk from testing the astronauts on the ISS?

Not really. While folks have stayed up on the space station for, say, 6 months at a time, the space station itself isn't in deep space. Rather, it orbits in what's called low Earth orbit. In low Earth orbit the cosmic radiation is nowhere near as harsh as it is elsewhere in the solar system. And that's because the space station still benefits from some of the protective effects of the Earth.

Even outside of Earth's safety zone, the longest Apollo mission was only 12 days. And other missions were even shorter than thata matter of hours. So it's hard to compare these to missions that are being talked about with interests now, like a trip to Mars and back, where you're talking about a much, much longer duration in space. A year or more.

Is there any way to shield against this radiation?

There are essentially two actions you can take. For one, you can come up with a physical countermeasure like shielding. Originally aluminum was picked because it was relatively lightweight, and is about 25 percent effective at blocking heavy ion radiation particles. And now people are looking into different types of polyethyleneplastics and other materials that look to be about 33 percent effective.

But even with shielding, some space radiation exposure is probably going to be fundamental. And so the second action is pharmacological. People are looking into a class of compounds called antioxidants, which almost everyone has heard of, and these are interesting because they can soak up certain [harmful molecules] caused by this radiation. There's also research looking at a wide array of other pharmacological solutions.

But nothing like Earth's magnetic field?

Well there's talk of putting some type of magnetic field around your spacecraft, but how that would work, and how you'd maintain it I'm not sure. I'm just a molecular biologist. But in principle it's something you would certainly think about.

By the time humans embark on something like a trip to Mars, do you think we will have eliminated the cosmic radiation risk?

I think that we will. Maybe not down to 0 percent, but it will be reduced all the way to a point that's deemed an acceptable level of risk. There are risks with every type of job: astronauts, coal miners, even people who work sitting down in an office.

As for whatever that acceptable level of risk might be, that's up to NASA to decide. But it's hard to make those calls until we figure out what the risks are now.

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