NASA GRAIL Mission Reveals True Nature of the Moon's Craters

NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission has revealed new insight into how the face of the moon received its rugged looks. It's found out a little bit more about the asymmetric distribution of lunar impact basins, which reveals a bit more about the history of the moon.

"Since time immemorial, humanity has looked up and wondered what made the man in the moon," said Maria Zuber, one of the researchers, in a news release. "We know the dark splotches are large, lava-filled, impact basins that were created by asteroid impacts about four billion years ago. GRAIL data indicate that both the near side and the far side of the moon were bombarded by similarly large impactors, but they reacted to them much differently."

Lunar impact basins have been difficult to study in the past mainly because there's been a lack of consensus on their size. Most of the largest impact basins on the near side of the moon have been filled with lava flows, which hide clues about the shape of the land that could be used for determining their dimensions. In order to learn a bit more about the lunar surface, the GRAIL mission measured the internal structure of the moon for nine months in 2012. With this data, the researchers were able to redefine the sizes of massive impact basins on the moon.

"Impact simulations indicate that impacts into a hot, thin crust representative of the early moon's near-side hemisphere would have produced basines with as much as twice the diameter as similar impacts into cooler crust, which is indicative of early conditions on the moon's far-side hemisphere," said Katarina Miljkovic, one of the researchers, in a news release.

The findings help redefine the concept of late heavy bombardment, a proposed spike in the rate of crater creation by impacts about 4 billion years ago. The late heavy bombardment is based largely on the ages of large near-side impact basins that are either within, or adjacent to the dark, lava-filled basins named Oceanus Procellarum and Mare Imbrium. The current work supports the idea that the size and distribution of impact basins on the far-side hemisphere of the moon is a more accurate indicator of the impact history of the inner solar system than those on the near side.

The findings are published in the journal Science.