"However, our research suggests that, in addition to the wicked cold, explorers and robots at the bottoms of polar lunar craters may have to contend with a complex electrical environment as well, which can affect surface chemistry, static discharge, and dust cling," said William Farrell of NASA's Goddard Space Flight Center.

Researchers created computer simulations to discover what happens when the solar wind flows over the rims of the craters.

They discovered that the dual electron-ion composition of the solar wind may create an unusual electric charge on the inside of the crater rim -- directly below the wind flow.

"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," says Farrell.

The negative charge along the leeward edge does not seem to build up indefinitely.

Eventually, an attraction between the negatively charged region and positive ions in the solar wind causes an anomalous electric current to flow.

The researchers suspect that the current could be generated by negatively charged dust repelled by the negatively charged surface.

It levitates and flows away from the highly charged 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," said Farrell.

"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."

The research has drawn praise from Farrell's colleagues.

"This important work by Dr. Farrell and his team is further evidence that our view on the moon has changed dramatically in recent years," said Gregory Schmidt, deputy director of the NASA Lunar Science Institute.

"It has a dynamic and fascinating environment that we are only beginning to understand."

The next step for Farrell and his colleagues is to create more sophisticated computer models of the lunar surface.

"We want to develop a fully three-dimensional model to examine the effects of solar wind expansion around the edges of a mountain," said Farrell.

"We now examine the vertical expansion, but we want to also know what happens horizontally."