The moon, Earth’s closest celestial neighbor, holds secrets beneath its familiar surface. A recent NASA study, drawing on data from the Gravity and Interior Recovery Laboratory (GRAIL) mission, has unveiled an asymmetrical structure deep within the lunar interior. This asymmetry helps explain the stark differences between the moon’s near side, visible from Earth, and its far side, which remained hidden until the space age.

Volcanism’s Role in Lunar Asymmetry

Scientists have long observed that the near side of the moon is dominated by vast, dark plains known as “seas,” or maria, formed by ancient solidified lava flows. In contrast, the far side presents a rugged, heavily cratered terrain with few such plains.The new research suggests that intense volcanism on the near side billions of years ago is the key to understanding this disparity.

The gravitational influence of Earth plays a crucial role.as the moon orbits, the near side experiences slightly more flexing than the far side due to “tidal deformation.” This difference in flexibility confirms significant variations in the lunar mantle between the two hemispheres, ultimately explaining their contrasting surface appearances.

A Warmer, More Active near Side

The study’s findings indicate that the lunar mantle beneath the near side is significantly warmer and more geologically active than its counterpart on the far side.

Our study shows that the interior of the moon is not uniform: the side that looks towards the earth – the nearby face – is warmer and more geologically active in depth than the distant face.
Ryan Park, supervisor of the solar system dynamics group at NASA’s Jet Propulsion Laboratory and lead author of the study published in Nature

Measurements reveal that the mantle of the near side is between 100 and 200 degrees Celsius hotter than that of the far side. This thermal difference is attributed to the concentration of heat-generating radioactive elements, such as thorium and titanium, on the near side.

The Lunar Mantle: Composition and Significance

The moon, with a diameter of approximately 2,160 miles, has a mantle that lies beneath its crust and above its core, extending from a depth of about 220 miles to 870 miles below the surface. This mantle, comprising roughly 80% of the moon’s mass and volume, is primarily composed of minerals such as olivine and pyroxene, similar to Earth’s mantle.

The fact that the asymmetry detected in the mantle coincides with the pattern of superficial geology…suggests that the processes that promoted the old lunar volcanism remain active today.
Alex Berne, a computer scientist from caltech affiliated with the Jet Propulsion Laboratory

GRAIL’s Gravitational Map: A Lunar Revolution

Scientists spent years analyzing data collected by the Ebb and Flow spacecraft of the GRAIL mission, which orbited the moon in 2011 and 2012. This effort yielded what Ryan Park describes as “the most detailed and precise gravitational map to the moon to date.”

this map not only enhances our understanding of the moon but also lays the groundwork for future lunar navigation systems, essential for upcoming exploratory missions. the methodology employed could also be applied to other celestial bodies, such as Enceladus (a moon of Saturn) and Ganymede (a moon of Jupiter), potentially aiding the search for extraterrestrial life.

The moon plays a vital role in stabilizing Earth’s rotation and generating ocean tides, influencing our planet’s ecosystems. Despite advancements in lunar science, manny questions about its deep structure remain, ensuring that our cosmic neighbor remains a captivating subject of scientific inquiry.