NASA: Some of moon's craters may be electrified
New NASA calculations suggest that solar wind blowing across the moon's surface may electrically charge polar craters.
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Since electrons are over 1,000 times lighter than ions, these lighter electrons in the solar wind rush into a lunar crater ahead of the heavier ions, creating a negatively-charged region within the crater.Skip to next paragraph
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The ions eventually fill the crater, but at consistently lower concentrations than that of the electrons. This imbalance in the crater makes the inside walls and floor acquire a negative electric charge. The researchers calculated that the electron/ion separation effect is most extreme on a crater's leeward edge – along the inside crater wall and at the crater floor nearest the solar wind flow.
Along this inner edge, the heavier ions have the greatest difficulty reaching the surface, unable to make the sharp turns over the mountain tops the way the lighter electrons can.
"The electrons build up an electron cloud on this leeward edge of the crater wall and floor, which can create an unusually large negative charge of a few hundred volts relative to the dense solar wind flowing over the top," Farrell said.
Still, the negative charge along this leeward edge won't build up indefinitely. Eventually, the attraction between the negatively-charged region and positive ions in the solar wind will cause some other unusual electric current to flow.
Electrified moon dust
The research team believes that a possible source for this current could be negatively-charged dust that is repelled by the negatively-charged surface that then gets levitated and flows away from the electrified region.
"The Apollo astronauts in the orbiting Command Module saw faint rays on the lunar horizon during sunrise that might have been scattered light from electrically lofted dust," Farrell said. "Additionally, the Apollo 17 mission landed at a site similar to a crater environment – the Taurus-Littrow valley. The Lunar Ejecta and Meteorite Experiment left by the Apollo 17 astronauts detected impacts from dust at terminator crossings where the solar wind is nearly-horizontal flowing, similar to the situation over polar craters."
To further this research, scientists want to create more complex computer models.
"We want to develop a fully three-dimensional model to examine the effects of solar wind expansion around the edges of a mountain," Farrell said. "We now examine the vertical expansion, but we want to also know what happens horizontally."
NASA is planning to launch the Lunar Atmosphere and Dust Environment Explorer (LADEE) as early as 2012, in a mission that will orbit the moon and could look for the dust flows predicted by the team's research
The details of the study were published March 24 in the Journal of Geophysical Research. The research is part of the Lunar Science Institute's Dynamic Response of the Environment at the moon (DREAM) project.
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