NASA’s latest analysis of the Moon’s interior is shedding new light on the longstanding mystery of why the Moon’s two hemispheres the near side facing Earth and the far side always turned away appear so dramatically different. The breakthrough findings come from data gathered by NASA’s GRAIL (Gravity Recovery and Interior Laboratory) mission, which orbited the Moon from 2011 to 2012.
The research team has identified significant asymmetries in the Moon’s mantle, the thick geological layer beneath its crust. They found that the nearside of the Moon flexes more during its orbit due to Earth’s gravitational pull, a phenomenon called tidal deformation. This subtle difference suggests the nearside mantle is geologically warmer and more active than the farside.
The nearside is dominated by vast, dark plains of solidified lava called “mare,” while the farside is mountainous and heavily cratered. Scientists believe this contrast is due to ancient volcanic activity concentrated on the nearside, which also caused the accumulation of heat-producing elements such as thorium and titanium. The study estimates that the nearside’s mantle could be up to 200°C hotter than the farside.
The enhanced gravity map developed from GRAIL’s Ebb and Flow spacecraft is now the most detailed ever produced of the Moon. It reveals how subsurface structures, temperature gradients, and radioactive elements shaped lunar geology over billions of years. These insights may also help guide future lunar missions by supporting the development of precise navigation and timing systems on the Moon’s surface.
Beyond lunar exploration, researchers say this method of analyzing gravity data can be extended to distant celestial bodies like Saturn’s Enceladus or Jupiter’s Ganymede—moons considered potential hosts for extraterrestrial life.
As NASA gears up for renewed human exploration of the Moon, the findings reaffirm the Moon’s significance not just as Earth’s stabilizing satellite, but also as a crucial scientific frontier.