A steady pounding by meteors, comets, and other space rocks gives the moon a high-power facelift—every 81,000 years. A new study published in Nature finds that pummeling reworks about the top inch of the entire lunar surface over that period, which happens to be "more than a hundred times faster than previous models estimated from meteoritic impacts (ten million years)." Using 14,092 paired before-and-after pictures snapped by NASA's Lunar Reconnaissance Orbiter, researchers mapped 222 new craters that have pocked the moon's surface in the past seven years. An estimated 80% of those craters are at least 30 feet in diameter; it's 33% more craters than expected. So why doesn't Earth's surface get similarly churned?
All credit goes to our "thick" atmosphere, where much of the more than 100 tons of space dust and smaller particles that shower the planet each day disintegrates, reports the AFP. Earth's atmosphere (measured at sea level) contains about 100 billion billion molecules per cubic centimeter compared with only 100 molecules per cubic centimeter for the moon. The thin-skinned surface means that future lunar astronauts are at risk of being whacked by space rocks. While the likelihood of a direct hit is low, the potential for being affected by a "splotch" is much higher. The researchers identified 47,000 "splotches," which occurred when an impact disturbs surface material such that it's catapulted into the air and comes down elsewhere, sometimes as far as miles away. (The moon once looked different from Earth.)