Apollo 11 astronaut Buzz Aldrin is shown standing beside the United States flag in July 1969. Photo / Getty Images
If we get back to the lunar surface, astronauts will have to contend with much more than perilous rocket flights and the vacuum of space.
Despite Nasa's successful Apollo landings, humans have spent very little time on the moon.
In total, 12 Apollo astronauts lived on the lunar surface for roughly 10 days, and travelled outside their lander for only 80 hours. With such a short sojourn, they caught merely a glimpse of the risks associated with survival there.
The prospect of humans staying on the moon for longer stretches has grown, with the Trump administration pledging an American return there by 2024, and China planning its first crewed trip to the lunar surface the following decade. That will require work by scientists to further assess the challenges. Here are the most serious risks.
Beyond the obvious hazards that arise from a rocket flight, zero-gravity nausea and a risky landing, the moon itself can be deadly.
When the Apollo astronauts walked on the moon, the dust clung to their spacesuits, scratched their visors and made their eyes water and their throats sore. It damaged the seals on the boxes of rock and soil that they brought back to Earth. It even smelled like gunpowder inside the lander.
Lunar dust, which is composed of shards of silica, is fine like a powder but it cuts like glass.
And that makes it toxic — so much so that Harrison Schmitt complained of "lunar dust hay fever" after his journey on Apollo 17. And yet, in total, Schmitt spent just 22 hours on the surface. Future astronauts might traverse the lunar landscape for much longer, giving them ample time to breathe in the deadly dust.
A recent study even suggests that prolonged exposure could lead to more serious effects, like bronchitis or cancer.
Then there is the moon's wrinkled surface — a topography that might be more threatening than rugged terrain on Earth.
"A lot of people think the moon is like a desert, but it's actually more like an ocean," Dr. Richard Scheuring, a flight surgeon at Nasa, said. "It has a very undulating surface, like sea swells."
Throw in the intense contrast between light and dark — unlike anything we see here on Earth — and those changes in the terrain can play tricks on your eyes.
When Pete Conrad and Alan Bean landed on the moon during the Apollo 12 mission, one of their tasks was to enter the 650-foot-wide Surveyor Crater. But as they skirted its rim, searching for the best path down, they informed Houston that the crater was far too steep.
Topographic maps, however, revealed an easy, 21-degree slope. The sharp shadows had fooled the astronauts.
That means the act of simply walking around on the moon might be perilous.
The moon might also be rippling. A recent study suggests that our lunar neighbour is tectonically active, with moonquakes as large as 5.5-magnitude earthquakes. That is bad news for future lunar bases, which might be vulnerable to the shaking.
Sleep may not come easy on the moon. Our body clocks are wound by light exposure, as day sweeps to night once every 24 hours. But on the moon, that same shift occurs once every 28 days.
An astronaut's circadian rhythm is going to be quite baffled. And the stakes are high. On Earth, sleep deprivation makes us fuzzy, but on the moon it is plain dangerous.
"Sleep is the biggest thing to protect for a crew member," Albert Holland, a Nasa psychologist, said. Without it, he added, astronauts might find themselves unable to face life-threatening emergencies.
When Nasa sent the Curiosity rover hurtling to Mars in 2011, it packed a stowaway: an instrument designed to measure the radiation throughout the trek.
The results confirmed that any astronauts beyond Earth's protective atmosphere and magnetic field would receive a hefty dose of radiation — one that is more than 200 times higher than levels on Earth. This is perhaps the biggest challenge.
Even aboard the International Space Station, which is so close to Earth that it is somewhat shielded, radiation levels are high — so high that when astronauts close their eyes, they often see flashes of light as cosmic rays pass through their optic nerve.
"It's an instantaneous reminder of the fact that those high-energy particles are going through your whole body — not just through your optic nerve," said Chris Hadfield, a Canadian astronaut who commanded the station in 2013. "And it's a stark reminder that you're no longer under the protective womb of the planet that nurtured us."
Those cosmic rays have the power to charge through both strands of DNA, snapping them in two and causing cancer. In addition, a dose of long-term radiation affects your cognitive abilities — resulting in dementia, memory deficits, anxiety, depression and impaired decision-making.
Radiation is not the only killer from deep space. On January 20, when stargazers across the Western Hemisphere watched a lunar eclipse, some saw a flash of light strike the moon's reddened surface. A small, fast-moving meteoroid had slammed into the moon.
Although the moon is a library of impact events, the flash was a reminder that collisions still occur today. Because the moon lacks an atmosphere, the strikes are hard and fast, posing a serious hazard for future astronauts.
Current spacesuits can block a 9-millimetre round, Scheuring said, "but a micrometeorite could be going a lot faster and it could be a lot bigger."
A trip will be possible only if scientists find ways to mitigate these challenges. And although a lunar habitat may never provide the protective bubble we take for granted on Earth, there may be a variety of options for safer lunar living.
To protect against lunar dust, Dorit Donoviel, the director of Nasa's Translational Research Institute for Space Health, said that any future lunar habitat would need filters and a strong airflow so that the astronauts would not breathe in the sharp silica. And Scheuring added that such a habitat would need a strong airlock where astronauts could clean off the dust before entering the main living area.
The habitat would also need to be equipped with lights to help counter the effects of sleep deprivation. Similar lights have already been installed on the space station, where individual sleeping compartments can be darkened to simulate night.
Just what that lunar habitat will look like remains a tough question, in part because radiation can penetrate most materials now used in space construction.
If living on the moon's surface for a sustained period is necessary, some experts have proposed covering shelters in a thick layer of water, because hydrogen works as a shield.
Another solution seems only natural: building living quarters underground. The lava tubes carved by ancient volcanic activity could potentially be turned into spacious living spaces.
All these hazards may seem worth it to anyone willing to be a moon dweller.
"Anything in life involves some risk," Hadfield said. "Often the more interesting and the more unusual the things you do with your life, the greater the inherent risk."
Written by: Shannon Hall
Illustrations by: Mike Lemanski
© 2019 THE NEW YORK TIMES
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