When Neil Armstrong and Buzz Aldrin returned from the moon, their cargo included nearly fifty pounds of rock and soil, which were packed in an aluminum box with seals designed to maintain the lunar surface’s low-pressure environment. But back at Johnson Space Center, in Houston, scientists discovered that the seals had been destroyed—by moon dust.
Lunar dust is fine, like a powder, but it cuts like glass. It’s formed when meteoroids crash on the moon’s surface, heating and pulverizing rocks and dirt, which contain silica and metals such as iron. Since there’s no wind or water to smooth rough edges, the tiny grains are sharp and jagged, and cling to nearly everything.
“The invasive nature of lunar dust represents a more challenging engineering design issue, as well as a health issue for settlers, than does radiation,” wrote Harrison (Jack) Schmitt, an Apollo 17 astronaut, in his 2006 book, “Return to the Moon.” The dust sullied spacesuits and ate away layers of moon boots. Over the course of six Apollo missions, not one rock box maintained its vacuum seal. Dust followed the astronauts back into their ships, too. According to Schmitt, it smelled like gunpowder and made breathing difficult. No one knows precisely what the microscopic particles do to human lungs.
The dust not only coats the moon’s surface, but floats up to sixty miles above it—as part of its exosphere, where particles are bound to the moon by gravity, but are so sparse that they rarely collide. In the nineteen-sixties, Surveyor probes filmed a glowing cloud floating just above the lunar surface during sunrise. Later, Apollo 17 astronaut Gene Cernan, while orbiting the moon, recorded a similar phenomenon at the sharp line where lunar day meets night, called the terminator. Cernan sketched a series of pictures illustrating the changing dustscape; streams of particles popped off the ground and levitated, and the resulting cloud came into sharper focus as the astronauts’ orbiter approached daylight. Since there’s no wind to form and sustain the clouds, their origin is something of a mystery. It’s presumed that they’re made of dust, but no one fully understands how or why they do their thing.
It’s possible that an electrical field forms at the terminator line—where sunlight meets shadow—that could knock dust particles aloft. Mihály Horányi, a physicist at the University of Colorado, in Boulder, has demonstrated that moon dust can indeed respond to such electric fields. But he suspects that the mechanism isn’t strong enough to create and sustain the mysterious, glowing clouds.
Data from a new mission should help scientists find a better explanation. While it’s been decades since American astronauts and rovers have explored the moon, lunar dust is of interest once again, with international and commercial space programs announcing a number of potential robotic and human moonshots. In September, NASA launched a small probe, the Lunar Atmosphere and Dust Environment Explorer, or LADEE, to analyze, for the next few months, the dust and molecules that surround earth’s only natural satellite.
The probe is about the size of a small car, and is encased in solar panels. Atop its nose are three boxy instruments: a dust counter partly designed by Horányi, and two chemical detectors to identify molecules like helium and sodium. Jutting from its side is the Lunar Laser Communication Demonstration, which sends data, like the number of large and small particles and their locations, back to Earth with a laser beam; it recently broke a record for the fastest communication between NASA and the moon, transmitting data nearly two hundred and forty thousand miles at six hundred and twenty-two megabits per second, or roughly seventy-one times the speed of the average broadband connection in the United States.
The two-hundred-and-eighty-million-dollar mission is well-timed, because LADEE’s detectors will get a relatively untainted picture of the dust density and chemical profile of the moon, ahead of expected traffic: China, India, Japan, and Russia have announced plans to launch moon probes and rovers in the coming years. Google’s Lunar X prize challenges engineers to build an unmanned craft with cameras to land on the moon and transmit “mooncasts” back to Earth by 2015. Golden Spike Company, another space startup, has ambitions for manned missions in the next decade or so.
When LADEE’s mission is over in a few months, the probe will join the barrage of fifteen tons of cosmic material that falls onto the moon every day, creating its own cloud of moon dust, just as it beams the last of its data back to Earth.
Kate Greene is a writer and recent crew member of a four-month simulated Mars mission called HI-SEAS. She lives in San Francisco.
Photograph by SSPL/Getty.