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Moon too static for astronauts?

February 2, 2007 By Philip Ball This article courtesy of Nature News.

Lunar settlements could face high-voltage sparks.

Lunar colonists could be in for a nasty shock — literally. A team of US scientists has found that the Moon's surface can become charged with up to several thousand volts of static electricity1.

This charging could release sparks that disable electronic equipment — including monitors, space buggies or even the front door of a Moon base. And it could cause dust clouds that clogs up instruments. What's worse, it can be caused by bad weather in space: just when astronauts need their equipment to give them warning and allow them to shelter from the radiation.

But not everyone sees the news as bad. "I'm overjoyed this work was carried out," says Dale Ferguson, a scientist at NASA's Marshall Space Flight Center in Alabama. "Data about the surface charging of the Moon was sorely lacking," he explains.

Jasper Halekas of the University of California, Berkeley and his co-workers knew that the Moon's surface could become charged when electrically charged particles in the solar wind plough into it. This process, they realised, could have left an imprint that the Lunar Prospector, which orbited the Moon in 1998-99, might have detected.

So Halekas and colleagues scanned through the data collected by the Lunar Prospector, and found that the surface charge can get as big as 4,500 volts. "That's more than enough to do some damage, if the electric field only extends over small distances," says Halekas. Any metal equipment would be vulnerable, though an astronaut might be protected by the insulation of his or her suit.

Halekas cautions that their observations were for charging over large areas, so the strength of local fields on the lunar surface is still unknown — if the charge is very spread out, then it might not cause a shock at all.

Blame it on the sunshine?

It's more than enough to do some damage.
Jasper Halekas
University of Californa at Berkeley
Two situations can lead to the lunar surface becoming highly charged. The first is when the Moon passes through the Earth's magnetotail — the magnetic wake left by the solar wind as it sweeps over our planet. The second is during 'solar storms', when streams of high-energy particles are hurled from the Sun out into space.

Sunlight can dissipate the charge by knocking electrons out of the surface, so most of the charge is seen on the night side of the Moon. But the researchers say they were surprised to find some shocking levels on the sunlit side too.

Could astronauts plan for this charging? The Moon's pass through the magnetotail is predictable. But outbursts of bad solar weather are not.

To detect or be alerted to the onset of a solar storm, astronauts need their electronic equipment. If the lunar surface became charged to thousands of volts, electrical sparks could burn out the equipment's circuits — just when they are needed most.

Fatal attraction

Solar storms can be disruptive on Earth. They interfere with radio telecommunication signals and disable satellites as the charged particles hit the upper atmosphere. In space, the effects can be even more alarming. The rain of particles can potentially damage living cells in much the same way as radioactivity, and so astronauts would need to take shelter behind protective screens. Staying out on the Moon's surface during a solar storm could be fatal.

Ferguson says, however, that the levels of charging seen on the Moon are similar to those found on satellites during solar storms. And there are already techniques to avoid spark damage, he says, for example by applying special surface coatings.

A bigger problem might be what the charging does to Moon dust. Charged dust particles would repel one another, and this could cause it to rise up in clouds.

"Levitated dust was seen on the Apollo missions," says Halekas — and the charging might now explain it. Moon dust is a big headache for exploration. "It sticks to everything and is very fine, so it gets past seals," Halekas says. It even clogged the vacuum cleaner that the Apollo astronauts took to keep their spacecraft clean.


  1. Halekas J. S., et al. Geophys. Res. Lett., 34. L02111 (2007).

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