Leaping Lunar Dust
Electrically charged lunar dust near shadowed craters can get lofted above the surface and jump over the shadowed region, bouncing back and forth between sunlit areas on opposite sides, according to new calculations by NASA scientists.
The research is being led by Michael Collier at NASA’s Goddard Space Flight Center, Greenbelt, Md., as part of the Dynamic Response of the Environment At the Moon (DREAM) team in partnership with the NASA Lunar Science Institute (NLSI), managed at NASA’s Ames Research Center, Moffett Field, Calif.
“The motion of an individual dust particle is like a pendulum or a swing,” says Collier. “We predict dust can swarm like bees around a hive over partially shaded regions on the moon and other airless objects in the solar system, such as asteroids. We found that this is a new class of dust motion. It does not escape to space or bounce long distances as predicted by others, but instead stays locally trapped, executing oscillations over a shaded region of 1 to 10 meters (yards) in size. These other trajectories are possible, but we now show a third new motion that is possible.” Collier is lead author of a paper on this research published October 2012 in Advances in Space Research.
This effect should be especially prominent during dusk and dawn, according to the team, as regions become partially illuminated while features like mountains and crater rims cast long shadows.
“The dust is an indicator of unusual surface electric fields,” says William Farrell of NASA Goddard, a co-author on the paper and lead of the NLSI DREAM team. “In these shaded regions, the surface is negatively charged compared to the sunlit regions. This creates a locally complex, larger electric field with separate positively and negatively charged regions, called a dipole field, over the shaded region. The dust performed its swinging motion under the influence of this dipole. Such a surface process occurring on the moon at the line where night transitions to day, called the terminator, might also occur at small bodies like asteroids. It might be a fundamental process occurring at airless rocky bodies.”
There is evidence that dust actually moves this way over the lunar surface. “There are hints for this type of dust swarm in Surveyor images. A twilight was observed over the landed platforms during dusk and dawn. This was surprising at first because the moon does not have a dense enough atmosphere to scatter light when the sun is below the horizon. It was long considered to be light scattered from lifted dust. This model suggests the dust is really leaping or swarming overtop a large number of shaded regions that would exist along the lunar dusk/dawn line, called the lunar terminator. It’s a natural fit. Charged lunar dust transport is also believed responsible for the Apollo 17 Lunar Ejecta and Meteorites (LEAM) experiment’s observation of highly charged dust near the terminator,” adds Collier.
For more information about the leaping lunar dust, visit: http://lunarscience.nasa.gov