PLANETARY SCIENCE: UV laser probes grains of Moon dust

In the Dusty Plasma Laboratory at the National Space Science and Technology Center (Huntsville, AL), Mian Abbas (with colleague Paul Craven and doctoral student Dragana Tankosic) observes changes in charge and other characteristics of a slightly charged single grain of lunar dust held in place by electric fields in a vacuum chamber under the illumination of a UV-laser beam.

“Experiments on single grains are helping us understand some of the strange and complex properties of moon dust,” Abbas said.

Apollo astronauts who walked on the Moon between 1969 and 1972 were surprised by the stickiness of Moon dust. Dust got on everything, fouling tools and spacesuits. Equipment covered by the dust absorbed sunlight and tended to overheat. The problem is likely to recur in the next decade because NASA’s Vision for Space Exploration projects that astronauts will be back on the Moon by 2018.

Like the Apollo astronauts, Abbas and his colleagues have already discovered surprises. “We’ve found two things,” he said. “First, ultraviolet light charges Moon dust 10 times more than theory predicts. Second, bigger grains (1 to 2 µm across) charge up more than smaller grains (0.5 µm), just the opposite of what theory predicts.”

When Apollo astronauts visited the Moon, they landed in daylight and departed before sunset. The next generation of explorers will remain much longer than Apollo astronauts did, however, eventually setting up a permanent outpost. So they will also need to know how Moon dust behaves around the lunar clock.

Consequently, in the second half of their experiment, planned for early this year, the researchers will bombard the dust with a beam of electrons. Theory predicts that lunar dust may acquire negative charge at night, when it is bombarded by free electrons in the solar wind-particles streaming from the Sun that curve around behind the moon and hit the night-dark soil.

The dust grains currently under study were returned by Apollo 17 astronauts in 1972 and the Russian Luna-24 spacecraft that landed on the Moon in 1976.