The Moon still retains a few mysteries even after a handful of humans explored its surface in the 1960s and '70s. The Moon is a big world and our limited explorations have only scratched its pockmarked surface. One of Luna's more intriguing mysteries was solved with some detective work started by a science fiction writer and completed by a team of NASA researchers.
An odd twilight glow on the Moon's horizon had long puzzled astronomers. First photographed by NASA's Surveyor robot landers, the mysterious lunar glow persisted after local sunset. The Moon's horizon also appeared to be hazy, yet researchers were at a loss to explain what caused the effect; the Moon has no atmosphere to speak of, so something was causing the odd dusky glow and haze.
In December 1972, Apollo 17 astronauts observed what they called "bands," "streamers" or "twilight rays" for several seconds before lunar sunrise and sunset. Similar rays were also reported by Apollo 8, 10, and 15 astronauts as well. After considerable study, lunar researchers couldn't come up with an answer that explained the strange extraterrestrial phenomena. It wasn't until recently that NASA scientists solved the Survey and Apollo puzzle--electrostatic charging was causing lunar surface dust to levitate.
Curiously, the researchers that solved the twilight ray mystery turned to the world of science fiction literature to find the answer.
"Back in 1956," according to NASA's Trudy Bell, "two years before NASA was even created, the late author Hal Clement wrote a short story called 'Dust Rag' published in Astounding Science Fiction magazine, about two astronauts descending into a crater on the Moon to investigate a mysterious haze dimming stars near the lunar horizon. After discarding a wild guess that they were seeing traces of a lunar atmosphere-'gases don't behave that way'-they figured it had to be dust somehow suspended above the ground." The lunar material was behaving as if it was being attracted to the fluffy fibers of Proctor & Gamble's Swiffer household duster!
In Clement's story, one of the fictional astronauts explained the lunar phenomena with relative ease: "...The [Moon's] surface material is one of the lousiest imaginable electrical conductors, so the dust normally on the surface picks up and keeps a charge. And what, dear student, happens to particles carrying like electrical charges? They are repelled from each other... And if a 100-km circle with a rim a couple of [kilometers] high is charged all over, what happens to the dust lying on it?"
According to the team that developed the new Dynamic Lunar Fountain Model to explain the effect-researchers J. Stubbs, Richard R. Vondrak, and William M. Farrell of the Laboratory for Extraterrestrial Physics at NASA's Goddard Space Flight Center-it was partially inspired by Clement's fictional story to help solve the mystery.
"The Moon seems to have a tenuous atmosphere of moving dust particles," Stubbs explained. "We use the word 'fountain' to evoke the idea of a drinking fountain: the arc of water coming out of the spout looks static, but we know the water molecules are in motion. In the same way, individual bits of Moondust are constantly leaping up from and falling back to the Moon's surface, giving rise to a dust atmosphere that looks static but is composed of dust particles in constant motion."
Lou Varricchio, M.Sc., is a former NASA science writer.