NASA scientists have long been puzzled by the Moon’s distinct halves. One side, always facing Earth, is smoother with vast dark plains. The opposite side is rugged and mountainous. Now, new research from NASA’s GRAIL (Gravity Recovery and Interior Laboratory) mission may finally explain this mystery.
Data from twin spacecraft, Ebb and Flow, shows that the Moon’s interior differs dramatically between the nearside and the farside. This discovery not only explains the surface contrasts, but also deepens our understanding of lunar evolution.
LUNAR TIDES REVEAL INNER ASYMMETRY
As the Moon orbits Earth, gravitational forces tug on it, causing tidal deformation. Scientists observed that the nearside bends more than the farside, indicating a softer, warmer interior beneath the side facing us. The farside, in contrast, is stiffer—suggesting a cooler, more rigid mantle.
The mantle, a dense layer between the Moon’s core and crust, is key to understanding this imbalance. According to the research, the nearside’s mantle is between 100–200°C warmer than its opposite.
VOLCANIC LEGACY SHAPES THE NEARSIDE
What heated the nearside? NASA researchers point to ancient volcanic activity. Billions of years ago, the nearside erupted in massive lava flows, producing the smooth plains known as maria. These eruptions also released radioactive elements like thorium and titanium, which are now concentrated beneath the surface.
These materials likely continue to emit heat, explaining the temperature difference today. The farside experienced far fewer eruptions and therefore stayed geologically colder and rougher.
SURFACE CLUES REFLECT DEEPER MYSTERIES
Ryan Park, the mission’s lead scientist at NASA’s Jet Propulsion Laboratory, emphasizes that the Moon’s surface features are connected to its interior.
“The interior isn’t uniform,” Park said. “The nearside is warmer and more geologically active. GRAIL data links heat patterns in the mantle with surface features.”
This connection helps scientists better understand how ancient processes still shape the Moon today. The Moon is no longer geologically active like Earth.
THE MOST ACCURATE GRAVITY MAP YET
GRAIL also delivered the most detailed lunar gravity map ever created. This map reveals subtle variations in the Moon’s gravity caused by differences in its internal structure.
“This detailed gravity map helps build better navigation systems,” said Park. “It will support future lunar exploration.”
Countries and companies are planning new missions to the Moon. Precise navigation data will be critical for safe landings. It will also be essential for exploration.
BEYOND THE MOON: TOOLS FOR OTHER WORLDS
This study doesn’t only help understand our Moon. It also opens the door for studying other moons in the Solar System.
By analyzing gravity, similar techniques could probe the interiors of Ganymede, Jupiter’s largest moon, or Enceladus, Saturn’s icy satellite. Both are prime candidates in the search for extraterrestrial life due to suspected underground oceans.
OUR NEAREST NEIGHBOR STILL HOLDS SECRETS
Though the Moon is Earth’s closest celestial companion, its complex history is still unfolding. It plays a critical role in stabilizing Earth’s rotation and controlling tides, yet continues to surprise scientists.
As NASA prepares for future Artemis missions, studies like GRAIL are essential in understanding the Moon’s deep structure and dynamic history. From mapping gravity to revealing hidden heat, this research highlights just how much we’re still discovering—about a place only 384,400 km away.