Astronomers Discover That The Earth's Magnetotail Charges The Surface Of The Moon

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strophysicists found that the moon's surface becomes electrified during each full moon. The moon passes through the Earth's magnetotail, a cone of highly-charged particles, for about 6 days each month. On the side of the moon facing the sun, ultraviolet particles disrupt the electromagnetic effect, keeping the voltage at low levels, but on the dark side, the voltage can reach hundreds or thousands of volts.

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"The surface of the moon can become electrified from charged particles in the surrounding space environment," says Timothy Stubbs, Ph.D., a space scientist at the NASA Goddard Space Flight Center in Greenbelt, Md.

This electric event happens once a month when the moon passes through the earth's magnetotail. A magnetotail is caused when the highly-charged particles of the solar wind zoom past the earth and mix with earth's magnetic field, creating a long tail that extends into the moon's orbit. "The moon is actually sitting in a sea of charged particles," Dr. Stubbs says.

Each month, the moon enters the magnetotail for six days. As it crosses inside the magnetotail, the moon's surface becomes highly charged.

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No astronaut has ever landed on a charged-up full moon to know exactly what happens, so learning more now will help astronauts in the future.

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WHAT IS THE SOLAR WIND? Flowing outward from the Sun's extremely hot corona, the solar wind is a stream of charged particles traveling in all directions at incredibly high speeds.

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Anyone can tell when the moon is inside the magnetotail. Just look: “If the moon is full, it is inside the magnetotail,” says Stubbs. “The moon enters the magnetotail three days before it is full and takes about six days to cross and exit on the other side.”

It is during those six days that strange things can happen.

During the crossing, the moon comes in contact with a gigantic “plasma sheet” of hot charged particles trapped in the tail. The lightest and most mobile of these particles, electrons, pepper the moon’s surface and give the moon a negative charge.

On the moon’s dayside this effect is counteracted to a degree by sunlight: UV photons knock electrons back off the surface, keeping the build-up of charge at relatively low levels. But on the nightside, in the cold lunar dark, electrons accumulate and surface voltages can climb to hundreds or thousands of volts.

Imagine what it feels like to be a sock pulled crackling from a dryer. Astronauts on the moon during a magnetotail crossing might be able to tell you. Walking across the dusty charged-up lunar terrain, the astronauts themselves would gather a load of excess charge. Touching another astronaut, a doorknob, a piece of sensitive electronics -- any of these simple actions could produce an unwelcome discharge. “Proper grounding is strongly recommended,” says Stubbs.

The ground, meanwhile, might leap into the sky. There’s growing evidence that fine particles of moondust might actually float, ejected from the lunar surface by electrostatic repulsion. This could create a temporary nighttime atmosphere of dust ready to blacken spacesuits, clog machinery, scratch faceplates (moondust is very abrasive) and generally make life difficult for astronauts.

Stranger still, moondust might gather itself into a sort of diaphanous wind. Drawn by differences in global charge accumulation, floating dust would naturally fly from the strongly-negative nightside to the weakly-negative dayside. This “dust storm” effect would be strongest at the moon’s terminator, the dividing line between day and night.

Much of this is pure speculation, Stubbs cautions. No one can say for sure what happens on the moon when the magnetotail hits, because no one has been there at the crucial time. “Apollo astronauts never landed on a full moon and they never experienced the magnetotail.”

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