It's not exactly a surprise that the moon is getting beaten up — this new model just adds a few more hits per year. Our solar system is full of debris left over from its formation, and the Earth and the moon are under constant bombardment: NASA estimates that the Earth is hit with more than 100 tons of dust and sand-sized particles every day, with larger rocks showing up fairly frequently. We have the atmosphere it takes to incinerate most of that space trash, and plenty of space for the occasional rock to invade without notice. Because the moon has no atmosphere to slow incoming debris, it takes the cosmic punches at full force.
“It's just something that's happening all the time,” study author Emerson Speyerer, an engineer at Arizona State University in Tempe, told Nature News.
By examining 14,000 before-and-after shots taken with the LRO, Speyerer and his colleagues were able to spot craters that may have gone unnoticed without a pre-impact surface that they used for comparison.
"When looking at just a single image, many of the newly formed features are indistinguishable from their surroundings," Speyerer told Space.com. "It's only with these detailed comparisons with previous images that we can separate out these small surface changes."
Based on these findings, it seems that the moon's surface might be "younger" — more recently changed — than previously assumed. The researchers suggest that the top two centimeters of loose moon dust could be totally reworked in just 81,000 years — which is 100 times faster than was predicted by previous models of moon evolution.
Do future astronauts, miners and moon colonists need to worry about impacts? Nature reports that the likelihood of a direct meteorite impact on a base — or human — is pretty slim. But the off-spray of smaller materials that has formed those 47,000 tiny "splotches" could pose a problem. Some splotches were found as far as 20 miles away from their associated impact crater. Any long-term lunar structures would have to be built to withstand impacts from dust particles moving at 1,120 miles per hour to avoid getting splotched, the researchers said.