Telling time on the moon
Ever since the solar system formed roughly five billion years ago, a steady barrage of asteroids, comets and other rocky material has pummeled the surfaces of planetary bodies. Earth’s surface shows little evidence of these so-called “impactors” thanks to weather, erosion and other geological processes that have altered Earth’s crust over time. But it’s a different story for the moon, where the lack of erosion and Earthlike tectonic activity has left the lunar surface pockmarked with billions of craters. Because these craters are like fingerprints of the impactors that made them, planetary scientists study lunar craters for clues about the massive objects that bombarded the planets during the early solar system. Now, for the first time, a team of researchers from MIT, Brown University and NASA’s Goddard Space Flight Center has mapped the entire surface of the moon, producing a catalog of every crater larger than 20 kilometers in diameter...