The invisible problem of sending people to Mars

Sending people to Mars is not easy. There are obvious challenges, such as getting people and supplies into space and landing them safely on another planet. Once they arrive, they will need a safe place to live, with air to breathe, water to drink, and food to eat. But the biggest obstacle to manned exploration of Mars may be something completely invisible and often overlooked: space radiation that can wreak havoc on the human body.

While Elon Musk is busy developing plans for a Mars city, experts in manned space exploration are more cautious. If we want people to explore Mars safely, getting to Mars might not even be the hardest part.

We know from decades of research on the International Space Station that microgravity has a range of effects on the body, from vision problems to muscle loss. But leaving Earth means leaving not only its gravity but also its protective bubble. We are only beginning to understand the many effects of exposure to space radiation on human health.

There are two main sources of space radiation: solar activity in the form of solar flares and high-energy particles called galactic cosmic rays. “Galactic cosmic rays come from dying stars and the radiation is part of the void of space as you travel,” explains radiobiologist and radiation expert Eleanor Blakely.

There are many health risks from space radiation, but little is known about them. It is thought to increase cancer risk, affect the central nervous system, increase degenerative effects such as heart disease and cataracts, and alter the immune system. Finding a way to mitigate these effects will determine whether astronauts can safely visit Mars, or whether health damage will make it too dangerous for people to set foot on Mars.

A special challenge of space exploration is that it requires long-term exposure to low levels of radiation, which is very different from most radiation exposure on Earth.

Most of the data we have looks at the health effects of radiation like gamma rays and Greg Nelson explains. But galactic cosmic rays travel through the body in straight lines like orbits. “So you concentrate the damage on a microscopic scale, and this damage, because it’s so concentrated, is much more difficult for the body to repair,” Nelson said.

This type of space radiation is different from the low-dose exposure from a chest X-ray. Instead, imagine a charged particle traveling at nearly the speed of light, directly through your brain, continuously perturbing 10,000 cells in a microsecond. It doesn’t necessarily damage these cells, but it activates them in a very unusual way. We don’t know yet what that does.

“It’s this feature, which we call orbital structure, that has the potential to create new and different effects,” Nelson said.

While most radiation on Earth causes cancer by damaging DNA, new research suggests these charged particles may damage the brain in entirely different ways, such as by damaging the connections between neurons or the mitochondria within them. .

Another concern is that astronauts are exposed to more than just radiation. During their journey into space, they also have to deal with microgravity, which is known to cause health problems.

There are also more obvious effects, such as loss of muscle tissue due to the muscles’ inability to resist gravity. But there is also evidence of other effects, such as brain remodeling. “This means that the tissue is activated in a different way than usual, such as a change in the amount of gray versus white matter,” Blakely explains. But as for the impact: “What are the psychological or physiological consequences? We don’t know.

Researchers set out to study how the effects of microgravity and radiation exposure compound.

“There is some evidence that they interact,” Nelson said. “No one knows yet whether it’s an additive effect, or whether it’s a synergistic effect.” In other words, it’s not clear whether these effects add to each other, or whether they combine to produce worse outcomes. Nelson points to evidence of changes in bone health, the blood-brain barrier in the central nervous system, and special features of the eye, all of which are open areas of research.

The combination of radiation exposure and sleep deprivation may also lead to increased cognitive deficits, according to recent studies in rodents. That’s not even considering the further impact of the psychological toll of isolation and confinement on long-duration space missions.

The health risks of space travel are many, and we don’t yet have enough information to understand how they interact.

NASA’s own calculations suggest that a longer mission to Mars could expose astronauts to more than 1 sievert of radiation, which exceeds the agency’s acceptable lifetime exposure limit. However, when sending people to Mars, the greatest radiation risk is during their travels. On the surface of Mars, there are some protections to avoid spending time on the planet’s surface, so the real concern is the time spent in space.

The effects are unlikely to be severe for up to a month. But when you start looking at time periods of six months to a year in space, “now you get into a range where, at least in rodent studies, you can see some changes,” Nelson said. “We’re still not quite sure how to extrapolate that to humans.”

You can choose when to travel to mitigate radiation risks. The sun goes through an activity cycle of about 11 years, and if you travel during its most active solar maximum period, there is more material from the sun that will scatter the cosmic rays. But this coincides with more solar particle events, so you have more solar radiation to worry about.

You can spend less time in space by using technologies like nuclear propulsion that NASA is working on, but this comes with its own risks – especially if something goes wrong during launch, as an explosion could blow away Radioactive material is scattered into the Earth’s atmosphere.

There are ways to protect astronauts from radiation, such as shielding. But it’s not a simple proposition either.

“Intuitively, we all think, ‘Oh, just put enough lead around me, make sure my underwear is lead, and I’ll be fine.'” For things like X-rays and gamma rays, this might is correct,” Nielsen said, especially when the radiation comes from one direction. But this is not the case for charged particles coming from all directions.

“With charged particles, one of the things that happens is they break into pieces,” Nelson said. “And smaller fragments can penetrate to greater depths than larger fragments. So sometimes more shielding can actually exacerbate the problem.

Radiation shielding has a “sweet spot” where it protects from a few large components without creating too many secondary components. Some of the most effective shields are actually materials like polyethylene rather than metal because it has more hydrogen atoms and is less likely to create small fragments.

You can build multiple layers of material that will act as protection in certain situations — such as allowing astronauts to sleep in more heavily shielded areas — but sooner or later astronauts will need to venture out and explore.

“Shielding is effective, but we have to accept the fact that we have to deal with amounts of radiation that cannot be shielded,” Nelson said.

NASA has strict limits on the amount of radiation that astronauts may be exposed to during their careers, which amounts to a 3-4% excess risk of death from all causes. These limits have recently changed, somewhat controversially, because it is difficult to derive safe amounts of radiation exposure. Different types of radiation affect people differently, depending on which parts of the body are exposed and factors such as the person’s age, gender and overall health.

“We must provide crews with informed risk assessments,” Nelson said. “If you go into space, that’s the risk you face – as far as we know, it’s your excessive risk in either category. And then the person has to make a decision. Are they willing to go out there regardless of certain interests? Does your family agree with this—to themselves, to NASA, and to the public at large?

When discussing health risks, astronauts are generally very willing to accept risks to their own safety. After all, space exploration is dangerous for many reasons, including the real danger that potential malfunction of a spacecraft or launch vehicle could lead to death. Beyond that, the risk of developing cataracts or increased risk of cancer seems less of a concern.

But agencies like NASA must also consider what family members and others think of life as an astronaut. “There are family stakeholders here who do have a stake in what’s going on and want to have a say in those decisions,” Blakely said. “When it’s folded back, it gives you a new perspective on what’s going on.” Look at the limits you put forward [for radiation exposure]”.

Thinking about the long-term health risks faced by astronauts, especially young astronauts, from the perspective of their families carries a different emotional weight than purely considering their own emotions. “I’m not sure if I’m a mother to those people, if I want to be that way,” Blakely said.

But considerations of personal harm must be balanced against the potential for discovery, including all that we can learn about the human body.

“People think exploration is important to our country for a lot of reasons, and we learn a lot about health from it. It’s awesome,” Blakely said.

Whether it’s the gleaming Martian cities Musk envisions or the more realistic idea of ​​a small group of explorers traveling to Mars for months to years before returning to Earth, the rewards of sending humans to another planet could be profound — —We just need to be clear about the cost.