Surprising number of meteoroids hit moon’s surface

The moon is one tough satellite. With no atmosphere, it endures a barrage of incoming asteroids and comets that pit its surface with a constellation of craters. A new map (above) reveals 222 recent impact craters (in yellow), 33 percent more than simulations predicted. Scientists spotted the features by analyzing about 14,000 pairs of before-and-after images captured by the Lunar Reconnaissance Orbiter from 2009 to 2015. (Red dots note new craters whose impacts were observed from Earth.)

The craters — up to 43 meters in diameter — were probably formed by small meteoroids crashing into the crust. Using the image pairs, the researchers created ratio images, which highlight how the impacts alter the reflectance of the moon’s surface. That perspective illuminated the starburst debris patterns around the craters (below, left).
The scientists also found about 47,000 “splotches,” faint marks several to tens of meters across (below right, before and after shown). Most result from secondary debris being jettisoned by impacts and spattering the surface, the researchers propose in the Oct. 13 Nature.
Those splotches would “churn” the upper two centimeters of lunar soil in about 81,000 years, more than 100 times faster than previous predictions that didn’t include the smudges, researchers say. That revelation could improve interpretations of remote-sensing data and help engineers design equipment to better withstand the occasional speckling of soil, says study coauthor Mark Robinson, a planetary geologist at Arizona State University in Tempe. “All of the images we’re taking … and the discoveries we’re making are feeding forward into future human exploration of the moon,” he says.