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Science Lecture by Timothy Stubbs |
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Date: January 24, 2007
Time: 10:30am
Location: NIA, Rm 137
Additional Information: Presentation (PDF)
The Lunar Dust-Plasma Environment: Implications for Science and Exploration
Timothy J. Stubbs, University of Maryland and NASA Goddard Space Flight Center
I will present evidence for the existence of a lunar dusty exosphere together with the results of recent modeling work to explain its formation and behavior. In addition, I will discuss how this relatively unknown environment could impact future scientific and exploration activities. From the Apollo era there is much evidence to suggest that lunar horizon glow observed at the terminator – e.g., by the TV cameras aboard the Surveyor landers and the Apollo coronal camera from orbit – is caused by sunlight scattered by dust grains originating from the surface. Evidence for dust transport was also provided by the Apollo 17 LEAM experiment, which detected highly charged dust grains near the lunar terminators moving at >100 m/s. The dust grains and lunar surface are electrically charged by the Moon’s interaction with the local plasma environment and the photoemission of electrons due to solar UV and X-rays. This causes the like-charged surface and dust particles to repel each other, and creates a near-surface electric field. The dynamic dust “fountain” model has been proposed to explain observations of submicron-sized grains “lofted” to altitudes in excess of 100 km. The surface potential that drives this dust transport varies depending on the ambient plasma environment. The Moon traverses the Earth’s magnetotail for about a quarter of its orbit and so interacts with the hot and tenuous plasma sheet environment, which results in much greater surface potentials. I will also discuss preliminary estimates of exospheric dust concentrations above the surface. These exospheric dust grains could significantly impact scientific activities, such as lunar-based astronomy. However, the more immediate concern is to what extent this dust-plasma environment will impede human and robotic surface operations. The Apollo astronauts experienced many problems with lunar dust, including its adhesion to everything. This behavior suggests that electrostatic forces are extremely important for understanding lunar dust processes, and so must be addressed in order to permit the successful exploration of the Moon.
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