The Moon’s surface is more complex than previously thought and was bombarded by two distinct populations of asteroids or comets in its youth, according to three new papers in the September 17 issue of Science that describe data from NASA’s Lunar Reconnaissance Orbiter (LRO).
Two of the papers describe data from LRO’s Diviner Lunar Radiometer Experiment instrument that reveal the complex geologic processes that forged the lunar surface. The data showed previously unseen compositional differences in the crustal highlands and confirmed the presence of anomalously silica-rich material in five distinct regions.
All minerals and rocks absorb and emit energy with unique signatures that reveal their identity and formation mechanisms. For the first time, the Diviner instrument is providing scientists with global high-resolution infrared maps of the Moon, enabling them to make a definitive identification of silicate minerals commonly found within its crust. “Diviner is literally viewing the Moon in a whole new light,” said Benjamin Greenhagen of NASA’s Jet Propulsion Laboratory in Pasadena, California, lead author of one of the Diviner papers.
Lunar geology can be roughly broken down into two categories — the anorthositic highlands, rich in calcium and aluminum, and the basaltic “maria,” giant impact basins filled with solidified lava flows that are abundant in iron and magnesium. Both of these crustal rocks are considered the direct result of crystallization from lunar mantle material, the partially molten layer beneath the crust.
Diviner’s observations have confirmed that most lunar terrains have signatures consistent with compositions in these two broad categories. But they have also revealed lunar soil compositions with more sodium than that of typical anorthosite crust. The widespread nature of these soils reveals that there may have been variations in the chemistry and cooling rate of the magma ocean that formed the early lunar crust, or they could be the result of secondary processing of the early lunar crust.
