NASA’s Jet Propulsion Laboratory reports that astronomers have figured out why the moon looks the way it does. The space agency says that data collected from the Gravity Recovery and Interior Laboratory mission has offered astronomers new information about this long-standing puzzle.

According to Maria Zuber, GRAIL principal investigator from MIT, astronomers have long wondered what created the so-called “Man in the Moon.” Scientists already know that the dark splotches on the moon were produced by asteroid collisions approximately four billion years ago and GRAIL information showed that both the near side and the far side of the moon were impacted similarly by humongous space objects, but they responded to these impactors in conflicting ways.

A lack of general agreement on their size, has made understanding lunar impact basins more difficult. For example, most of the largest impact basins on the near side of the moon have been filled with lava flows, which conceal important data about the form of the land that could be utilized for determining their size. Fortunately, GRAIL data helped astronomers arrive at a consensus on the sizes of the dark splotches on the moon.

Interestingly, maps of crustal thickness created by GRAIL revealed more large impact basins on the near-side hemisphere of the moon than on the far side. Why is this? Astronomers point out that the temperatures on the near-side hemisphere of the moon were greater than those on the far side: amounts of the heat producing elements uranium and thorium are greater on the near side than the far side, thus, most volcanic eruptions happened on the moon’s near-side hemisphere.

According to Katarina Miljkovic of the Institut de Physique du Globe de Paris, simulations reveal that impacts into a hot, thin crust much like the primitive moon’s near-side hemisphere would have generated impact basins with as much as twice the diameter as similar impacts into cooler crust, which is representative of the early environment on the moon’s far-side hemisphere.