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'Deflector shields' protect the lunar surface

Posted on 19 July 2012

Scientists at the Rutherford Appleton Laboratory and the University of York have solved a lunar mystery. They have identified the origin of the enigmatic "lunar swirls" – swirling patches of relatively pale lunar soil, some measuring several tens of kilometres across.

During the era of the Apollo moon landings, researchers realised that lunar swirls were associated with localized magnetic fields in the lunar crust (so-called lunar 'magnetic anomalies').

Unmanned spacecraft, such as NASAs Lunar Prospector, identified that magnetic anomalies created fully formed but miniature “magnetospheres” just as the Earth’s planetary wide magnetic field does on a much larger scale.

Using a combination of the space data and laboratory scale experiments using a “Solar Wind Tunnel” at the York Plasma Institute at the University of York, the team were able to identify how such small scale magnetic “bubbles” were more efficient in deflecting the solar wind particles that bombard the moon.

Dr Kieran Gibson, who led the laboratory studies at the York Plasma Institute, says: “Our experiments provide a great opportunity to mimic in the laboratory a range of effects of the solar wind, from studies like this of the aging of the surface of the moon through to testing ideas for protecting spacecraft from solar storms.”

Project lead scientist Dr Ruth Bamford of the Centre for Fundamental Physics and RAL Space at the Rutherford Appleton Laboratory, and an Honorary Visiting Fellow in the Department of Physics at York, says:  “When we first tried these experiments in the Solar Wind Tunnel and they worked, it was very exciting.

“The active force which deflects the solar wind particles is electric not magnetic. The electric field is created naturally at the edges of the moon's magnetic 'bubbles". What matters is the "gradient" in the magnetic field, rather than the overall size of the magnetic bubble. So they can be as small as you like - as long as the gradient is steep enough.”

Understanding how "mini-magnetospheres" produce a cavity in the solar wind and exclude the interplanetary magnetic field might lead the way to determining if the same mechanism could be artificially manipulated to create safe havens for future space explorers.

Our experiments provide a great opportunity to mimic in the laboratory a range of effects of the solar wind

Dr Kieran Gibson

“We still need to determine quite how effective this mechanism would be at deflecting the real hazardous higher energy particles. The jury is still out on that one, but such an active shield could make the difference between survivable and certain death for astronauts on their way to Mars,” Dr Bamford says.

The lunar soil is known to have is been darkened over time by exposure to the charged particles of the "solar wind".

It had been thought that the swirls were a result of magnetic shielding of the lunar surface from the solar wind. But how the relatively weak magnetic fields associated with lunar swirls could protect the moon's surface over hundreds of millions of years to prevent surface darkening and produce such finely detailed patterns remains unresolved.

Dr Bamford adds: "Close to the moon's surface, the strength of a magnetic anomaly is likely to be very irregular, featuring overlapping "cavities" and "gradients". Over an estimated 3.8 billion years these anomalies would have been deflecting the solar wind particles streaming in from space, slowly creating these amazing patterns, which can be clearly seen on the lunar surface today.”

Details are to be published in the scientific journal Physical Review Letters and at Physics Archive http://arxiv.org/abs/1207.2076.

This work is thanks to the support from RAL Space, Space Weather initiatives and the Center for Fundamental Physics. 

 

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