Asteroid strikes cause the Moon's surface to smooth

Though other craters have similar rings, the lunar surface surrounding the Orientale basin is unusually rough with reduced concavity. The anomalous features were identified by Kreslavsky and Head after they produced a map of the lunar surface topographic roughness using observations from the Lunar Orbiter Laser Altimeter aboard the Lunar Reconnaissance Orbiter.

The fact that other craters -- even those of similar size and age -- lack similar features suggests to the authors that mechanisms such as weathering or gravitational settling cannot explain the anomaly. Instead, the authors suggest that the Orientale basin, which formed about 3.8 billion years ago, stands out simply because it is the youngest large crater.

They propose that whenever a large body slams into the Moon, seismic waves produced during the impact travel through the solid lunar material, inducing seismic shaking that causes landslides and surface settling. They estimate that the impactor would need to be at least 100 km (62 mi) across to cause sizeable seismic shaking.

Unfortunately, the authors may need to wait more than a little while to conclusively test their hypothesis -- until the Moon is next rocked by a massive asteroid, an event not expected to occur in the foreseeable future.