Moon dust mystery mostly solved

Recovered data from Rice experiments pays off 40 years later for former professor 

Devices invented and built at Rice University in the 1960s have been gathering dust on the moon for more than 40 years, as intended. The physicist who created the matchbook-sized dust detector experiments (DDE) is using recently recovered data to determine the rate at which lunar dust has been alighting on the devices’ solar-panel surfaces.

Brian O’Brien, left, then a Rice professor, and his student David Reasoner work on a moon-bound experiment in the 1960s. Photo courtesy of the Fondren Library

What former Rice professor Brian O’Brien has learned should be of interest to public and private space exploration organizations as they consider return trips to the moon.

O’Brien, who left Rice in the late ’60s to go back to his native Australia, concluded in a paper that appeared in the journal the American Geophysical Union publication Space Weather this month that troublesome lunar dust only accumulates at a rate of about a millimeter every thousand years.

Yet that’s more than researchers expected, and it’s enough to cause concern for future lunar explorers who need solar power to live.

“You wouldn’t see it; it’s very thin indeed,” said O’Brien, now a professor at the University of Western Australia, in a press release. “But, as the Apollo astronauts learned, you can have a devil of a time overcoming even a small amount of dust.”

The new revelations spring from data collected over six years following NASA’s moon missions from Apollo 11 through 15. (The program ended with Apollo 17 in 1972.) DDEs were part of science packages to test not only dust accumulation but also to monitor the long-term effects of radiation and thermal energy on their solar cells. O’Brien used data from seven DDE solar cells on the last three of these missions (12, 14 and 15) in his latest analysis.

The dust detector experiment is the small box at left attached to a package of experiments left on the moon by Apollo 12. Photo courtesy of NASA

O’Brien found the dust, which accumulated at a rate of 100 micrograms per square centimeter each year, blocked enough light to measurably cut voltage produced by the solar cells. He compared dust’s effects on covered but unhardened cells to long-term damage from solar radiation and found the dust was worse. Even the bombardment by particles from an intense August 1972 solar outburst didn’t cause as much long-term harm as the slow buildup of moon dust, he said.

The DDEs were added to the Apollo scientific packages when NASA realized the lunar module would likely kick up enough dust upon liftoff to coat experiments left behind. They returned data to NASA until September 1977, when the experiment was shut down.

Unfortunately, tapes of the data were not archived, and NASA thought the data was lost forever – until O’Brien heard about the problem and revealed a few years ago that he has a set of backups. A search for a machine to read them found a vintage IBM tape drive in an Australian computer museum.

Rice’s Patricia Reiff, who helped NASA analyze data from experiments in the same package while working as a Rice graduate student, recalled that data from the moon got to Houston, but its path from there took a sharp left turn. “One of the real tragedies of the program was a lot of the original data tapes were written over,” said Reiff, a professor of physics and astronomy and associate director of public outreach for the Rice Space Institute. NASA was in the process of replacing its antiquated data storage system in the ’70s, “and that took a long time, so they had to take a lot of old data tapes and reuse them.

“We had sent all our data back to the National Space Science Data Center thinking it was safe, but a lot of the data tapes at the NSSDC got reused. And the data tapes we had here at Rice were all ruined in the great flood of 1976, when the basement of the Space Science Building got flooded,” she said.

Watch a 2008 video interview with O’Brien here.

Scientists want to know why dust continues to move about on a body in space that has little gravity and no atmosphere. O’Brien suggested meteor impacts and cosmic dust around enough to account for the amount settling on the cells. One theory is that charged dust particles – positive under sunlight and negative on the dark side under the influence of the solar wind — are “levitated” at the transition between night and day.

“Something similar was reported by Apollo astronauts orbiting the moon who looked out and saw dust glowing on the horizon,” said Monique Hollick, a researcher at Western Australia and the paper’s co-author. NASA now has an opportunity to confirm the levitation theory with the Lunar Atmosphere and Dust Environment Explorer launched in September.

“It’s been a long haul,” O’Brien said. “I invented (the detector) in 1966, long before Monique was even born. At the age of 79, I’m working with a 23-year-old working on 46-year-old data, and we discovered something exciting. It’s delightful.”