NASA Reveals Why the Moon Has Two Faces
News Desk
Islamabad: An exhaustive analysis of lunar gravity, using data from NASA’s twin GRAIL (Gravity Recovery and Interior Laboratory) spacecraft, is offering critical insights into why the moon’s two hemispheres — the near side always facing Earth and the far side perpetually turned away look so dramatically different.
The study, published in the journal Nature, reveals that the moon’s deep interior has a distinctly asymmetrical structure. This internal imbalance appears to be the result of intense volcanic activity on the near side billions of years ago, which profoundly influenced the moon’s surface and thermal makeup.
“We found that the moon’s interior is not uniform,” said Ryan Park, lead author of the study and supervisor of the Solar System Dynamics Group at NASA’s Jet Propulsion Laboratory (JPL) in California. “The side facing Earth — the nearside — is warmer and more geologically active deep down than the farside.”
The new gravitational data suggests that during the moon’s elliptical orbit, the nearside flexes slightly more than the farside due to Earth’s gravitational pull — a phenomenon known as tidal deformation. This variation further confirms internal differences, particularly within the moon’s mantle, the thick layer between its crust and core.
The moon’s nearside is characterized by vast plains of solidified lava known as mare, while its farside remains rugged and cratered with few such plains. Scientists have long hypothesized that heat-producing radioactive elements, such as thorium and titanium, accumulated on the nearside, driving ancient volcanic activity that shaped its distinct features.
The GRAIL data now offers the most compelling evidence yet to support that theory. Researchers estimate the nearside mantle is between 180–360°F (100–200°C) hotter than the farside, with the temperature difference likely sustained by radioactive decay.
“The detected asymmetry in the mantle matches the pattern of surface geology — especially the concentration of 3–4 billion-year-old volcanic basalts on the nearside,” said Alex Berne, a computational planetary scientist at Caltech and co-author of the study.
The GRAIL mission, which operated from December 2011 to December 2012, involved two robotic spacecraft — Ebb and Flow — which mapped the moon’s gravitational field in unprecedented detail.
“This is the most detailed and accurate gravitational map of the moon ever produced,” Park said. “It lays the foundation for developing lunar Positioning, Navigation, and Timing (PNT) systems, which are crucial for the success of upcoming lunar exploration missions.”
These findings not only enhance understanding of lunar history but also have implications for other celestial bodies. The techniques used in this study may be applied to icy moons such as Enceladus and Ganymede — promising candidates in the search for extraterrestrial life.
As NASA prepares for future missions to the moon and beyond, this new research underscores the enduring importance of Earth’s closest celestial neighbor.
“The moon plays a vital role in stabilizing Earth’s rotation and generating ocean tides,” Park noted. “Though we’ve learned much through decades of human and robotic exploration, many questions about the moon’s deep interior and history remain. It continues to be a key to unlocking the secrets of our solar system.”
