New moon craters form more frequently than astronomers earlier predicted as the surface of the moon is pummeled by meteorites more often than expected. The findings raises concerns regarding the safety of future lunar missions given the increased possibility these can be hit by falling space rocks.

Researchers from Arizona State University compared more than 14,000 photos taken by the Lunar Reconnaissance Orbiter, which has been orbiting and mapping the surface of the moon since 2009. By looking at images of the same site taken over different periods of time, researchers discovered that the moon has about 33 percent more craters than earlier predicted.

They found 222 craters measuring more than 140 feet wide that they did not expect to see. They also discovered 47,000 changes in the so called splotches, splatter-like stains on the surface of the Earth's natural satellite. Many of these splotches were found clustered around new impact sites. Many of these were found lying very far from the crater that may have caused them.

Scientists think surface regolith, or the soil in the moon's surface, caused the splotches as they were churned up by debris that were flung out from the original crater impact.

Based on their findings, the researchers estimate that the top 0.8 inches of lunar dirt gets fully churned every 81,000 years or so, which is over 100 times faster than previously estimated based on meteoritic impacts.

"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," said study author Emerson Speyerer, from Arizona State University at Tempe. "It's only with these detailed comparisons with previous images that we can separate out these small surface changes."

The discovery also suggests that a number of young features on the lunar surface, which include recent volcanic deposit may also be younger than previously thought.

"Here we use Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) temporal ('before and after') image pairs to quantify the contemporary rate of crater production on the Moon, to reveal previously unknown details of impact-induced jetting, and to identify a secondary impact process that is rapidly churning the regolith," the researchers reported in their study, which was published in the journal Nature on Oct. 12.

Researchers said their findings have implications when planning for lunar base or a long term habitat that may be set up on the moon.