"The Martian" hero Mark Watney survived all that the Red Planet threw at him, including frigid temperatures, unbreathable air and relatively high radiation levels.
This last danger wasn't explicitly addressed in the hit 2015 movie or the best-selling book it was based on, said Ron Turner, an expert in astronaut radiation-risk management at the security and defense analysis group ANSER.
"I loved the book and the movie," Turner told Space.com by email. "Both were silent on the radiation risk, and since I have been working on astronaut radiation-risk management for a long time, it was just natural for me to be curious about what the risk would be." [Mars Radiation Threat to Astronauts Explained (Infographic)]
So Turner decided to quantify that risk, authoring an in-house paper that examines the radiation threat to both Watney and his fellow Mars explorers, who managed to escape the planet during a powerful dust storm. (Watney got separated from his crewmates, who thought he had died, and therefore left him behind.)
Turner's analysis shows that Watney fared better than the evacuees in this department, who would have received higher doses of radiation as they cruised through space on their ship, which is called Hermes. Indeed, the Hermes crew might have felt the effects of these doses while still in space, the study suggests.
Safer while stranded
Once they leave Earth, astronauts are exposed to increased radiation levels from two main sources: the high-energy particles that stream from the sun during solar storms, and ubiquitous galactic cosmic rays (GCRs), electron-free atomic nuclei accelerated to nearly the speed of light by faraway supernova explosions and other dramatic events.
The amount of radiation experienced by astronauts on a crewed Mars mission would depend partly on when that mission occurred. Though the book and movie don't explicitly state when Watney and his crewmates blast off on their Ares 3 mission, clever people have deduced — and "The Martian" (Crown, 2014) author Andy Weir has confirmed — that the astronauts touch down on the Red Planet in November 2035.
In that year, the sun will be near the maximum of its 11-year activity cycle. At that time, powerful solar storms could occur as often as once a month, and could last anywhere from several hours to several days, an obvious concern for astronauts on Mars or in deep space.
"The key for solar storms is providing a warning architecture of solar-monitoring satellites and instruments that measure radiation levels in real time in the habitats and [that are] carried with the astronauts, so they know they need to stay in shelter," Turner said. [The Worst Solar Storms in History]
During a big solar storm, astronauts on the surface of Mars, such as Watney, would likely be restricted to their habitat, Mars Ascent Vehicle (MAV) or rovers, which would feature extrastrong shielding, Turner added. Watney's crewmates in space would need to remain in the more heavily shielded regions of the Hermes, following procedures similar to those practiced by astronauts on the International Space Station (ISS) today.
Turner said 4 to 12 inches (10 to 30 centimeters) of shielding can help reduce radiation from solar storms to safe levels. Strategically positioning supplies, water and even waste can help form a barrier against fast-moving particles.
The atmosphere of Mars, though far thinner than Earth's, would also provide Watney and other Martian visitors with some protection from solar storms. The planet itself serves as another shield, blocking particles from the storms at night, when Mars' rocky bulk stands between the astronaut and particles streaming from the sun.
Watney was initially stranded without any communications link to NASA, so he could not have picked up any warnings sent regarding upcoming solar storms, at least not at first. But he still likely would have been OK on the Martian surface, Turner said.
"Since Mark spent most of his time in the rover or in the habitat, and since the atmosphere does a good job of attenuating solar radiation, Mark would not be at substantial risk, even if he did not know a solar storm was underway, in all but the worst possible solar storms," Turner said.
Indeed, Watney would receive only about 10 to 20 percent of the radiation exposure from solar storms experienced by his crewmates aboard the Hermes, Turner said..
Scheduling a mission during solar maximum may seem like a bad plan, but it may actually be the best time to travel, Turner said. When the sun is at its peak activity, the more dangerous GCRs have difficulty pushing their way through the solar wind and the sun's magnetic field, and radiation dosages are cut in half, Turner said.
It takes significantly thicker shields to protect astronauts from GCRs compared with radiation from solar storms. A reasonable thickness would stop only the lower-energy particles, Turner said, reducing the radiation dose by half or less. Lightweight materials such as aluminum can help by scattering the particles, as can strategically placed supplies within the spacecraft.
Back on Mars, Watney would receive significantly less GCR radiation than the Hermes crew. While the spacecraft would be bombarded from all directions, the planet would block radiation coming from beneath, cutting the dosage in half. The atmosphere, though thin, would block even more rays, cutting Watney's total dosage to about one-third that of his colleagues. [Will Radiation Kill Mars Astronauts? (Video)]
Watney experienced another source of radiation when he dug up the Mars outpost's radioisotope thermoelectric generator (RTG), to use the instrument's decaying plutonium as a heat source. Turner didn't have the exact details on the system, so he didn't calculate how this might have affected the astronaut.
"However, in talking with other experts on this power source, it is likely that it would have only produced a small increase in the overall background radiation," he said. "RTGs are generally relatively easy to shield and safe to employ."
So, despite being stranded and starving, it looks like Watney would have come out ahead of his crewmates, at least where radiation dosage is concerned.
The effects of radiation wouldn't be limited to an increased risk of cancer after returning to Earth. NASA is now changing its focus from just long-term risks to also include those that might manifest during the course of a long-duration mission, Turner said.
Housing astronauts on ISS for increasingly longer missions — such as the one-year voyage recently completed by NASA astronaut Scott Kelly and cosmonaut Mikhail Kornienko — provides one way to look into this issue.
Astronauts exposed to extensive radiation could experience decreased cognitive performance, increased susceptibility to infection and increased risk of cardiovascular failure, all due to gradual cell damage and tissue degradation, researchers have said. Another documented problem is the gradual growth of cataracts in the eyes. All of these issues could potentially impair a Mars crew while on its mission.
The Ares 3 crew has the advantage of not being the first humans to set foot on Mars. In the universe of "The Martian," two other groups of astronauts had previously visited the Red Planet and returned safely, presumably unimpaired despite flying during the solar minimum, when radiation from GCRs was at higher levels. But only a dozen astronauts were exposed, and Turner pointed out that the effects of radiation vary widely among individuals. Also, the astronauts of Ares 3 spent far more time in space and on Mars than any previous crew had done.
"Andy Weir takes a different approach to advanced concepts by assuming advanced propulsion to reduce the travel time substantially over current NASA plans," Turner said. "This may be the best approach, and a variety of advanced-propulsion schemes are under study, but at a relatively low level."
The problem is developing and testing such a plan before the end of the 2030s, the current goal for sending a crewed mission to Mars, Turner said.
You can read Turner's study, which is called "The Radiation Threat to 'The Martian,'" here: http://www.anser.org/docs/The_Radiation_Threat_to_the_Martian.pdf