Natural shield: NASA astronaut Alan L. Bean, walks on the Moon during the Apollo 12 mission of November 1969. Future moon colonists should plan their moonwalks for periods when the lunar surface is protected from cosmic rays by the Earth's magnetic field, say scientists.

Credit: NASA

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NEW YORK: For about seven days a month, the Moon’s orbit carries it inside the protective cocoon of Earth’s magnetic field, where it is partially shielded from the Solar System’s turbulent space weather. Could future colonists use this to their advantage?

A new study suggests that space agencies could use this natural radiation screen when constructing lunar bases or planning the moonwalks of future astronauts.

“The terrestrial magnetic field provides a significant amount of shielding for energetic particles incident on the Moon,” said Robert Winglee, a physicist at the University of Washington in Seattle, USA. “An astronaut, especially if he was far off from base, would be very well protected.”

Catching some rays

Research suggests that prolonged exposure to solar and cosmic rays can lead to increased cancer rates, and providing proper shielding against such radiation is a major challenge for NASA’s planned Moon and Mars missions.

Scientists have known for years that the Moon spends about a quarter of its time each orbit in the elongated tail end of our planet’s magnetosphere; the region surrounding Earth where its magnetic field dominates, but whether this could be used to safeguard humans on the Moon was unclear.

A new computer model developed by Winglee and co-worker Erika Harnett, also of the University of Washington, attempts to tackle this question.

The results, detailed in a recent issue of the journal Geophysical Research Letters, suggests the protection is substantial, and that the terrestrial magnetic field can deflect charged particles from the Sun and low-energy cosmic rays that would otherwise bombard the Moon’s surface.

The model predicts certain lunar areas, like the Earth-facing parts of the Moon’s poles and equator, are better protected by Earth’s magnetic field than others.

Space weather

It does not, however, address the degree to which the Moon is protected against more powerful solar storms such as solar flares or higher-energy cosmic rays. It is these things that pose the greatest threats to lunar explorers, commented Daniel Baker, a space weather expert at the University of Colorado in Boulder, who was not involved in the study.

“Out at the Moon, you're in an extraordinarily weak magnetic field region,” Baker said. “These very energetic particles...are not going to be highly deflected by these very weak magnetic fields.”

Until more studies are done, Baker thinks planners should be cautious about relying on the Earth’s magnetic field to protect lunar astronauts. “One might think ... this a magic bullet and it’s going to save the human lunar exploration program, but I don't think we're in that boat yet,” he said.