Lunar swirls -- wispy bright regions scattered on the Moon's surface -- were created by the numerous comets that crashed into the lunar surface over the past 100 million years, says a new study.
The researchers used computer models to simulate the dynamics of comet impacts on the lunar soil. The simulations suggest that such impacts can account for many of the features in the mysterious swirls.
"We think this makes a pretty strong case that the swirls represent remnants of cometary collisions," said Peter Schultz, planetary geoscientist at Brown University in Rhode Island in the US.
Lunar swirls have been the source of debate for years. The twisting, swirling streaks of bright soil stretch, in some cases, for thousands of miles across the lunar surface.
Most are found on the unseen far side of the Moon, but one famous swirl called Reiner Gamma can be seen by telescope on the southwestern corner of the moon's near side.
Comets carry their own gaseous atmosphere called a coma.
Schultz thought that when small comets slam into the Moon's surface -- as they occasionally do -- the coma may scour away loose soil from the surface, producing the bright swirls.
The simulations showed that the scoured area would stretch for perhaps thousands of kilometres from the impact point, consistent with the swirling streaks that extend across the Moon's surface.
"This is the first time anyone has looked at this using modern computational techniques," Schultz said.
"Everything we see in simulations of comet impacts is consistent with the swirls as we see them on the Moon," Schultz said.
The study was published in the journal Icarus.
