The same magnetic field that protects Earth from radiation could pose a hazard to astronauts on the Moon, a new study suggests. The magnetic field can dump electrons onto the Moon鈥檚 surface, potentially damaging electronics and stirring up dangerous lunar dust.
The Moon spends most of its time well outside of Earth鈥檚 magnetic field. But once each orbit it moves through Earth鈥檚 long 鈥榤agnetic tail鈥�, which sweeps out behind the planet in the direction opposite the Sun.
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Embedded in this tail is a region called the plasmasheet that is full of energetic electrons. When the Moon passes through this region, the electrons slam into the lunar surface and charge it with static electricity, a phenomenon observed by NASA鈥檚 Lunar Prospector mission in 1998.
Static electricity could be a serious problem for lunar astronauts, because it can lead to 鈥榮parks鈥� 鈥� electric discharges that can damage electronics. It can also cause troublesome lunar dust to levitate above the surface, where it can more easily contaminate spacesuits and other equipment, possibly posing health risks (see Lint rollers may collect dangerous Moon dust).
Now, new research suggests this static electricity could be much worse for the next group of astronauts visiting the Moon than it was for the Apollo astronauts.
18-year cycle
This is because the amount of time the Moon spends in the plasmasheet, where it can mop up electrons, varies on an 18-year timescale. The variation is related to the tilt of the Moon鈥檚 orbit, which can make the Moon pass above, below, or through the plasmasheet.
鈥淭he total amount of exposure varies by a factor of two or three,鈥� says Mike Hapgood of the Rutherford Appleton Laboratory in the UK.
Static electricity would have been at a minimum during the Apollo missions, Hapgood says, but will be high at the time of NASA鈥檚 planned return to the Moon in 2020. That is just past the maximum length of time the Moon spends in the plasmasheet, which occurs around 2016 to 2018.
鈥淚f you鈥檙e thinking about going to the Moon and building a permanent presence there, then all these space environment issues are important,鈥� Hapgood told New 杏吧原创.
Sticky dust
Sandra Wagner, head of planetary environment management and integration at NASA鈥檚 Johnson Space Center in Houston, Texas, US, says NASA is interested in how electrical charges affect lunar dust.
鈥淭here are people who say that static electricity is going to be a big problem because the dust carries charge,鈥� she told New 杏吧原创.
鈥淥thers say the dust will stick to things because it carries a charge, but won鈥檛 necessarily cause a big potential difference鈥� in voltage that could damage electronics, she continues. 鈥淲e鈥檙e just trying to find out what is the reality as far as risk and then . . . we can start thinking about how to mitigate.鈥�
Hapgood says there may be ways to reduce any problems. Many airplanes, for example, have rods protruding from their wings to let static electricity leak away into the atmosphere, although this particular solution would not be ideal for use on the airless Moon.
Night risk
鈥淭here are technologies around for handling static electricity,鈥� Hapgood says. 鈥淲e need to understand how to put these into the design of systems.鈥�
Hapgood says one good thing is that the problem should be reduced during the lunar day, when astronauts are likely to be most active. That is because sunlight knocks electrons off the lunar surface, thereby reducing the charge.
But astronauts may not be able to avoid going outside at night entirely, so the potential static electricity hazard should be investigated further, he says: 鈥淲e need to quantify the risk and understand what it means.鈥�
Hapgood is presenting his research on the 18-year static electricity cycle at the Royal Astronomical Society鈥檚 National Astronomy Meeting this week in Preston, UK.
