Joan Wong; Photos courtesy of NASA

From 1969 to 1972, 12 men walked on the moon. Four of them are still alive. No one has been back since, and it’s unclear when anyone might return.

The four moonwalkers were in their mid to late thirties when they flew millions of miles to visit Earth’s celestial companion. Today, in their 80s, their hair is the color of the lunar surface. They remain in the public eye, giving talks and interviews, especially now, as the historic Apollo missions begin marking their 50th anniversaries. But someday the moonwalkers will leave us, taking with them the living memory of a transcendent experience the rest of us can hardly fathom.

For the youngest generations, the idea of the moon landings, captured in crackly black-and-white footage, might seem as distant as the moon itself.

The moon was a weird place to be.

Aldrin, now 89 years old, felt disoriented as he took in the sight. “On the Earth when one looks at the horizon, it appears flat; on the moon, so much smaller than the Earth and quite without high terrain, the horizon in all directions visibly curved away from us,” he wrote in a memoir in 1974.

Thanks to the airless environment and the lunar soil, as fine as talcum powder, the astronauts never had to worry about getting lost. “Everywhere you walk, you left your footprints,” said Charlie Duke, who visited in 1972, at an event last year. “You just turn around and follow your tracks back.”

David Scott, who became the first person to drive on another world in 1971, likened the undisturbed landscape to a picture by the photographer Ansel Adams. “There was no color, but great contrast between the brightly illuminated surface and the black shadow of the mountain slopes and craters where no sunlight fell,” he wrote in a 2004 memoir. And the smell! “The moon turned out to have a slightly metallic smell, almost like gunpowder, which pervaded the [lunar module] for the remainder of our trip,” Scott recalled.

These experiences and others are well documented—in grainy footage and scratchy audio, flight transcripts, books, documentaries, Hollywood films, and countless news reports and interviews. There’s a wonderful little clip of Jack Schmitt, one of the four remaining moonwalkers, pleading with Mission Control to let him throw his hammer into the lunar sky before getting into the lander to go home. Schmitt, 84 years old now, is the first and only scientist—a geologist—to have visited the moon, and it must have seemed appropriate to leave behind his profession’s tool of choice. “Look at that!” he exclaimed after the flight directors assented and the hammer tumbled, end over end, a small white smudge moving in an arc over the hulking gray background. Schmitt had spent a total of 22 hours outside the capsule, helping to produce the biggest haul of lunar samples.

But these records are not as evocative as hearing from the moonwalkers themselves, says Charlie Bolden, a former space-shuttle astronaut who served as NASA administrator in the Obama administration. When the last moonwalker dies, “it will be like the day we lose the last veteran of World War II—and we’re perilously close to that day—or the last Korean War veteran,” Bolden says. “You will lose any semblance of opportunity to listen to people and hear their firsthand experience.”

Bolden had that chance in 1980, as a new NASA recruit from the Marine Corps. The Apollo astronauts would stop by the NASA astronaut office in Houston once a year for their annual physical exams and reminisce with the newbies. Alan Bean, the Apollo moonwalker who died last year at age 86, was a mentor to Bolden’s class during training.

“Here’s a guy who had walked on the moon, who gave up a year of his life when he could be doing all other kinds of things, to shepherd around these snotty-nosed kids who aspired to be astronauts,” Bolden says. “You know how you see the day-school caregivers walking around with the kids on a rope? That’s kind of the way it felt.”

The Apollo astronauts’ memories of the surface are easier to preserve than the distinct cognitive experience of looking back at the Earth. Some astronauts who travel into Earth’s orbit say they come home with a distinct shift of perspective on the planet. From up there, this ball of swirling blues and whites, suspended in the inky blackness of space, looks fragile, especially against the perilous backdrop of climate change. The effect would only be magnified on the moon, where Earth appears like a gleaming marble. “We have seen it from space as whole and bright and beautiful; we have seen it from the surface of the moon as not very large and somehow vulnerable,” Aldrin wrote in his book. “With all its imperfections, it is a great place to come from and an even greater place to go back to.”

Joan Wong; Photo courtesy of Getty

The Apollo astronauts who had touched the surface of the moon were walking testaments to human achievement. They seemed to ooze unalloyed inspiration. When you ask people to consider the morbid, hypothetical reality of a world without them, most often you hear about that inspiration—and how depressing it would be to lose it.

An estimated 600 million people around the world watched Aldrin and Neil Armstrong descend that ladder on live television. Pamela Melroy, a former shuttle astronaut who helped assemble the International Space Station, was among them, a 7-year-old girl on vacation with her family on the Jersey shore. “We all watched Star Trek together—let’s put it that way—so we were all kind of nerdy anyway,” Melroy says. “I don’t remember what I thought at the moment, but I do know that within two years, I had made the decision that I wanted to be an astronaut.”

Melroy says she dreads the day the last Apollo moonwalker dies. “I sure as heck hope that we will have somebody who has walked on the moon since before the last one passes away,” she says.

President Richard Nixon correctly predicted in 1972, as the crew of the last lunar mission flew home, that “this may be the last time in this century that men will walk on the moon.” But after pulling off the feat—six times in three and a half years, at that—it seemed hard to imagine the possibility that no one would ever return.

The current White House has instructed NASA to send a crewed mission to the lunar surface in 2024 and has asked Congress for the extra money to pay for it. The effort is not guaranteed, and the roadblocks are numerous, ranging from technical risks to political shifts, and another country may beat it there. The next crew, should it ever arrive, probably won’t resemble the astronauts of the Apollo era, who were white men with similar educational and military backgrounds. The Trump administration says NASA’s new Artemis program, named for Apollo’s sister in Greek mythology, will deliver the first woman to the surface.

Bolden hopes the crew includes people of color and astronauts from other nations too. He watched the first moon landing in Mississippi, where he was in jet training for the Marine Corps. He was mesmerized, but the event didn’t inspire him to become an astronaut.

“I’d grown up in the segregated South,” Bolden says. “Becoming an astronaut was not something in the list of things that a young black kid from South Carolina did, in my mind.”

He applied to the NASA astronaut corps a decade later, at the urging of Ron McNair, a member of NASA’s 1978 class of astronauts, the first new group since the Apollo program. McNair was the second African American man to fly to space. He died in the Challenger disaster six years after Bolden got the job.

“I needed to see somebody like me,” Bolden says now.

In the past few rounds of astronaut applications, prospective candidates cited the space-shuttle missions, not the moon landings, as motivation, according to those who reviewed them. This year, Millennials will surpass Baby Boomers as the largest adult population in the United States, according to an analysis of government data by the Pew Research Center. The Apollo program was not the defining moment of space exploration for members of this generation, born from 1981 to 1996. They remember their teachers wheeling bulky televisions into classrooms to watch a space-shuttle launch or tuning into livestreams on their laptops to watch a SpaceX rocket fly. They summon images of Elon Musk and Jeff Bezos more readily than of Neil Armstrong and Buzz Aldrin.

When the Apollo 11 astronauts returned to Earth, they were unlike any other travelers in history. But they still had to follow the rules governing entry to the United States, which explains the existence of perhaps the most ridiculous copy of a customs entry form on record.

Where the form requested a departure location, NASA wrote “moon.” The cargo was “moon rock and moon dust samples.” As for whether the travelers experienced any conditions on board that could lead to the spread of disease, NASA wrote, “to be determined.” Scientists and doctors had no idea what the lunar environment could do to the human body, so Armstrong, Aldrin, and Michael Collins spent a month in quarantine.

The document is delightful and silly, but it marked a shift in a millennia-old perception of the flat orb of light in the night sky. It made clear to travelers who would never leave Earth that the moon was a real place, somewhere people could truly go. Not only that, but they could do things there.

Some scientists thought the surface would be soft, and the astronauts would sink, but it held them well, and the dust clung to their spacesuits and drove them nearly crazy trying to wipe it off. The astronauts scaled the gentle slopes and went for a drive. They enjoyed a quiet, freeze-dried meal, slipped into their sleeping bags, and pulled the shades down in their capsule to soften the radiant sunlight bouncing off the Earth. And when they left, their footprints remained, preserved in the unmoving regolith for tens of thousands of years.

The Apollo astronauts made a home on another world. For a brief moment, humankind extended beyond the boundaries of its planet, “a mote of dust suspended in a sunbeam,” in Carl Sagan’s words. Without the moonwalkers, its jurisdiction shrinks back, toward this one familiar planet, which soon could be the only place that living people have set foot.

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