Earth’s surface, we’re protected from this onslaught by the thick air over our heads. But an astronaut in orbit is essentially naked, exposed to the wave of photons. A spacewalker caught by surprise will absorb many of the incoming X-rays, getting the equivalent of hundreds or even thousands of chest X-rays in a single flash.
X-rays are dangerous because when absorbed, they deposit all their energy into tissue. This can lead to cell and DNA damage. When DNA is damaged, mutations can occur that can (but do not always) lead to cancer.
Radiation absorption is measured in units called rems. 11 Natural radiation coming up from the Earth’s surface surrounds us all the time; you get a dose of about 0.3 rem per year just by existing on the Earth. In high-altitude locations, like Denver, that can be as high as 0.5 rem due to both terrestrial and extraterrestrial sources. A dental X-ray, by comparison, gives a dose of about 0.04 rem, one-tenth of your normal annual background dose. The U.S. government has guidelines for employees who work in elevated radiation environments: the maximum safe whole-body dose is set at 5 rems per year.
A mild flare may expose an astronaut to several dozen rems of radiation. While that sounds bad, in fact the body can heal itself fairly well after such a one-time radiation dose. Cells heal, and small amounts of damaged DNA can be eradicated by the body’s natural defenses. That’s not to say it’s fun: the problems associated with this kind of dose are irritated skin and a higher risk of developing skin cancer or other forms of cancer. Male astronauts might also experience a temporary sterility lasting for a few months, and hair loss in both sexes is possible.
But if too much tissue is damaged, the body cannot heal itself. In a major flare, an astronaut could absorb hundreds of rems of X-rays. This can be fatal: there is simply too much cell damage for the body to repair itself. Over the course of several hours and days the astronaut suffers a slow death as cells die, the intestinal lining sloughs off, ruptured cells leak fluid into their tissue . . .the effects are horrifying. NASA takes this threat very seriously. When a flare is seen on the Sun, astronauts on the International Space Station retreat to a section that is more protected, letting the station itself absorb the radiation to safeguard the humans inside.
When astronauts return to the Moon they’ll have to deal with this as well. Lunar rock is an excellent absorber of radiation, so it’s likely that lunar colonists will cover their habitats with two or three yards of rock and rubble. It’s not as romantic as glass domes on the surface, but being able to actually survive a flare may take precedence over our preconceived notions of what a colony should look like from watching science-fiction movies. 12
In a major flare, though, not just humans are in danger: our satellites can be fried as well. When an X-ray or a gamma ray from a flare hits the metal in a satellite, the metal becomes ionized. A very high-energy gamma ray can ionize many atoms in the satellite, causing a cascade of electron “shrapnel” to fly off the atoms. Remember, moving electric charges create a magnetic field. This sudden strong pulse of magnetic energy can damage electronic components inside a satellite (just as a magnet can damage your computer’s drive). The electrons themselves might short-circuit the hardware too.
Many civilian satellites have been lost in solar flare events. Military satellites are in many cases protected from this damage, and such radiation-hardened satellites can still operate even if there is a major flare. The effects of a nearby nuclear blast are similar to those of a flare, so these satellites may also survive a nuclear detonation in space (as long as debris and heat from the blast doesn’t get them).
Moreover, the Earth’s atmosphere absorbs the incoming high-energy light. While that protects us on the surface, the upper
X-rays are dangerous because when absorbed, they deposit all their energy into tissue. This can lead to cell and DNA damage. When DNA is damaged, mutations can occur that can (but do not always) lead to cancer.
Radiation absorption is measured in units called rems. 11 Natural radiation coming up from the Earth’s surface surrounds us all the time; you get a dose of about 0.3 rem per year just by existing on the Earth. In high-altitude locations, like Denver, that can be as high as 0.5 rem due to both terrestrial and extraterrestrial sources. A dental X-ray, by comparison, gives a dose of about 0.04 rem, one-tenth of your normal annual background dose. The U.S. government has guidelines for employees who work in elevated radiation environments: the maximum safe whole-body dose is set at 5 rems per year.
A mild flare may expose an astronaut to several dozen rems of radiation. While that sounds bad, in fact the body can heal itself fairly well after such a one-time radiation dose. Cells heal, and small amounts of damaged DNA can be eradicated by the body’s natural defenses. That’s not to say it’s fun: the problems associated with this kind of dose are irritated skin and a higher risk of developing skin cancer or other forms of cancer. Male astronauts might also experience a temporary sterility lasting for a few months, and hair loss in both sexes is possible.
But if too much tissue is damaged, the body cannot heal itself. In a major flare, an astronaut could absorb hundreds of rems of X-rays. This can be fatal: there is simply too much cell damage for the body to repair itself. Over the course of several hours and days the astronaut suffers a slow death as cells die, the intestinal lining sloughs off, ruptured cells leak fluid into their tissue . . .the effects are horrifying. NASA takes this threat very seriously. When a flare is seen on the Sun, astronauts on the International Space Station retreat to a section that is more protected, letting the station itself absorb the radiation to safeguard the humans inside.
When astronauts return to the Moon they’ll have to deal with this as well. Lunar rock is an excellent absorber of radiation, so it’s likely that lunar colonists will cover their habitats with two or three yards of rock and rubble. It’s not as romantic as glass domes on the surface, but being able to actually survive a flare may take precedence over our preconceived notions of what a colony should look like from watching science-fiction movies. 12
In a major flare, though, not just humans are in danger: our satellites can be fried as well. When an X-ray or a gamma ray from a flare hits the metal in a satellite, the metal becomes ionized. A very high-energy gamma ray can ionize many atoms in the satellite, causing a cascade of electron “shrapnel” to fly off the atoms. Remember, moving electric charges create a magnetic field. This sudden strong pulse of magnetic energy can damage electronic components inside a satellite (just as a magnet can damage your computer’s drive). The electrons themselves might short-circuit the hardware too.
Many civilian satellites have been lost in solar flare events. Military satellites are in many cases protected from this damage, and such radiation-hardened satellites can still operate even if there is a major flare. The effects of a nearby nuclear blast are similar to those of a flare, so these satellites may also survive a nuclear detonation in space (as long as debris and heat from the blast doesn’t get them).
Moreover, the Earth’s atmosphere absorbs the incoming high-energy light. While that protects us on the surface, the upper
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