NASA Scientists Unravel Mystery of Moon's Surface Swirls

New observations of the Moon have shed light on the origin of the distinctive swirls on the lunar surface.

Scientists have moved a step closer to solving the mystery of puzzling swirls on the surface of the moon, using computer models to test various hypotheses of their origin, NASA reported on Friday.

According to lunar observations, the swirls appear where ancient bits of magnetic field are embedded in the lunar crust. They also have bright areas which appear to be less weathered than their surroundings.

Researchers have hypothesized that the swirls and the magnetic fields formed from plumes of material ejected by comet impacts, or that micrometeorite impacts propelled fine dust particles upwards, which were then sorted by an existing magnetic field.

A third theory holds that since particles in the solar wind (electrons and ions) are electrically charged, they respond to magnetic forces. 

This is an image of the Reiner Gamma lunar swirl from NASA's Lunar Reconnaissance Orbiter

© NASA . LRO WAC science team

This might cause the surface to be shielded by the magnetic field from weathering by the solar wind, a stream of electrically conducting gas blown from the surface of the sun that blows at millions of kilometers per hour.

"The problem with the magnetic shield idea is that the embedded magnetic fields on the moon are very weak – about 300 times weaker than Earth's magnetic field," said NASA physicist Bill Farrell.

"It's hard to see how they would have the strength to deflect the solar wind ions."

However, according to the new computer models, the magnetic field can create a strong electric field when the solar wind attempts to flow through, which could deflect and slow particles in the solar wind and lessen their weathering of the swirls.

"Until you have somebody making measurements on the lunar surface we may not get a definitive answer, but the new observations that analyze the swirls in ultraviolet and far-ultraviolet light are consistent with earlier observations that indicate the swirls are less weathered than their surroundings," said John Keller, project scientist for NASA's Lunar Reconnaissance Orbiter Project, a robotic mission to map the moon's surface.