The scientists also found broad zones around these new craters that they interpreted as the remains of jets of debris following impacts. They estimated this secondary cratering process is churning the top 0.8 inches (2 centimeters) of lunar dirt, or regolith, across the entire lunar surface more than 100 times faster than thought.
"I'm excited by the fact that we can see the regolith evolve and churn - a process that was believed to take hundreds of thousands to millions of years to occur - in images acquired over the past several years," Speyerer told Space.com.
These new findings also suggest that a number of young features on the moon's surface, such as recent volcanic deposits, "may in fact be even a bit younger than previously thought," Speyerer said.
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Although the odds of something on the lunar surface suffering a direct hit by asteroidal or cometary debris is very small, Speyerer noted these new findings illustrate the potential dangers posed by the rocks kicked up by these impacts.
"For example, we found an 18-meter (59-foot) impact crater that formed on March 17, 2013, and it produced over 250 secondary impacts, some of which were at least 30 kilometers (18.6 miles) away," Speyerer said. "Future lunar bases and surface assets will have to be designed to withstand up to 500 meter per second (1,120 mph) impacts of small particles."
Speyerer said that NASA recently approved a two-year extended mission for the Lunar Reconnaissance Orbiter that can help collect more before-and-after images of the lunar surface.
"As the mission continues, the odds increase of finding larger impacts that occur more infrequently on the moon," Speyerer said. "Such discoveries will enable us to further refine the impact rate and investigate the most important process that shapes planetary bodies across the solar system."
The scientists detailed their findings online in today's (Oct. 12) issue of the journal Nature.
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