Lunar swirls may be caused by crashing comets

Brett Smith for redOrbit.com – Your Universe Online

Swirls of dust on the lunar surface have baffled scientists for decades, but a new computer-simulation-based study has found that these odd swirls were caused by the Moon colliding with various comets.

Published in the journal Icarus, the study used computer models to emulate the dynamics of comet strikes on the lunar soil. The models show that these impacts can explain many of the characteristics in the swirls.

“We think this makes a pretty strong case that the swirls represent remnants of cometary collisions,” study author Peter Schultz, a planetary geoscientist at Brown University, said via press release.

Comets have been suspected as the cause in the past, but the swirls don’t quite appear to be impact craters and this appearance may have fueled the mystery surrounding them. One theory for the way the swirls may have formed said rocks below the swirls might hold remnant magnetism from early in the Moon’s history. Some scientists suggested that those powerful, local magnetic fields deflect the barrage of the solar wind, which may slowly darken the Moon’s surface. The swirls would remain more brilliant than the surrounding soil due to those magnetic shields, the theory said.

Based on Apollo

Schultz’s said his comet theory was based on watching the lunar modules land during the Apollo program.

“You could see that the whole area around the lunar modules was smooth and bright because of the gas from the engines scoured the surface,” Schultz said. “That was part of what got me started thinking comet impacts could cause the swirls.”

Schultz speculated small comets might slam into the lunar surface, resulting in its gases scouring away loose soil from the surface. The scouring is what produces the bright swirls, Schultz said.

The study team used computer simulations to show the impact of a comet plus its gases would lead to blowing off the smallest grains that sit atop the lunar soil. The models revealed that the scoured region would stretch for perhaps thousands of miles from the impact point, similar to the swirling streaks that extend across the lunar surface. Vortices produced by the gaseous impact would also explain the swirls’ twisted appearance.

The models also showed when iron-rich particles on the lunar surface are melted by the impact and then cooled; they record the presence of any nearby magnetic field.

“Comets carry with them a magnetic field created by streaming charged particles that interact with the solar wind,” Schultz said. “As the gas collides with the lunar surface, the cometary magnetic field becomes amplified and recorded in the small particles when they cool.”

“This is the first time anyone has looked at this using modern computational techniques,” Schultz added. “Everything we see in simulations of comet impacts is consistent with the swirls as we see them on the Moon. We think this process provides a consistent explanation, but may need new Moon missions to finally resolve the debate.”

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Source: http://www.redorbit.com/news/space/1113401722/lunar-swirls-may-be-caused-by-crashing-comets-060215/