There's a crescent Moon in the west this evening. Even though it's only a tiny sliver, you may just make out the scars of giant impacts -- the dark lunar seas. Billions of years ago, giant asteroids slammed into the Moon, forming wide basins. Molten rock filled these basins to form the dark volcanic plains.
The Moon still gets hit today. But most of the impacts are tiny -- they're by small bits of rock and metal known as micrometeorites.
Like a steady rainfall here on Earth, this shower of particles churns up or "gardens" the surface. The meteorites come in so fast that they break up or melt the rocks, forming a powdery surface layer known as regolith. Repeated impacts till this layer like a farmer plowing a field.
KUHLMAN: As the micrometeorites come in, they continuously garden the sample -- they turn it over. Larger ones garden it more.
Kim Kuhlman is a researcher at the Planetary Science Institute. She's studying this process and others that "weather" the lunar surface.
KUHLMAN: The top layer gets turned over very frequently. The farther down you go, the less frequently it gets turned over. It takes a large event to turn over to two meters.
Studying this process can help scientists understand the history of the lunar surface. It can also help them understand other space weathering processes that could help future explorers extract resources from the Moon. More about that tomorrow.