Something Unusual detected Inside the Moon

 NASA Just Found Something Odd Inside The Moon

A decade-long NASA study has uncovered unexpected secrets lurking deep inside the Moon and asteroid Vesta, reshaping what we know about their ancient pasts. It is thought that volcanic activity on the lunar near side (the side facing Earth) helped create a landscape dominated by vast plains called mare, which are formed by molten rock which cooled and solidified. The interior beneath the nearside and the far side of the Moon is very different.... and that difference continues underneath. Since the first observation of the far side of the Moon in the 60s, it has been clear that there are major differences between the side of the Moon that we always see and the one that is always pointing away from us. The newest analysis has revealed that this difference is not skin-deep, but profound. The Moon’s interior on the nearside is different from that on the far side.  

A pair of ground breaking NASA studies, have unveiled new insights into the interiors of the Moon and the asteroid Vesta, two drastically different celestial bodies. By leveraging precise gravity data from orbiting spacecraft, researchers have mapped subtle internal variations without ever touching the surface. The findings challenge long-held assumptions about both objects, shedding new light on the history and makeup of planetary bodies in our solar system. Analysis of data collected by the NASA Gravity Recovery and Interior Laboratory (GRAIL) mission has shown that there is a distinct temperature difference on the closer side of the Moon. The research team computed the Moon’s tidal Love numbers, values that describe how a celestial body deforms under an external gravitational force. Study delivers the most detailed and accurate gravitational map of the Moon to date.

Rather than relying on physical sampling or seismic data, the researchers used a gravitational mapping technique which tracks how spacecraft subtly shift due to a body’s gravity. The Moon’s internal structure was analysed using data from NASA’s GRAIL mission, while Vesta’s structure was derived from the Dawn mission. This allowed the researchers to create a highly accurate, high-resolution map of the gravitational field of the Moon. It is in that map that the dichotomy between nearside and far side was found to extend deeper than thought. “Our study shows that the Moon’s interior is not uniform: the side facing Earth (the nearside) is warmer and more geologically active deep down than the far side. This difference is linked to the Moon’s volcanic history and explains why the two sides look so different,” lead author Dr Ryan Park, senior research scientist, said. “The Moon’s nearside and far side look very different, as shown by differences in topography, crustal thickness and the amount of heat-producing elements inside. These differences may come from variations deep within the Moon, causing one side to be warmer and more volcanic. Until now, there hasn’t been clear proof of these deep differences.”

“Gravity is a unique and fundamental property of a planetary body that can be used to explore its deep interior,” said Ryan Park, lead author and supervisor of the Solar System Dynamics Group at NASA’s Jet Propulsion Laboratory. “Our technique doesn’t need data from the surface; we just need to track the motion of the spacecraft very precisely to get a global view of what’s inside.” The data suggests that the mantle on the nearside might be “softer” than the mantle on the far side by 2 or 3%. A small value, with big consequences. The temperature on the nearside mantle might be higher by 100 to 200°C (180-360°F), possibly due to the presence of radioactive material which has kept this side warmer for billions of years. Many spacecraft have conducted observations of the interior of planets and moons by using gravity. Although not quite as detailed as GRAIL, this work has delivered new insights into Earth, Mars, Venus, Mercury, and the moons of the gas giants. Just a few months ago, observations from Juno revealed that the volcanic moon Io might be more solid than thought.  This approach allowed the team to measure tiny changes in orbital velocity and position, enough to infer complex subsurface differences. The method has opened a new frontier in planetary exploration, capable of revealing the deep structures of moons, asteroids and even distant dwarf planets.

“By measuring how a planet’s gravity field changes as a spacecraft orbits, we can infer important properties about its internal structure-such as whether it is rigid, contains a liquid layer or has significant variations in density,” Dr Park explained. “As measurement techniques and technology continue to improve, future missions will be able to provide even more detailed and accurate gravity data, opening up new possibilities for studying distant worlds.” The Moon’s near and far sides are famously different: the near side is smoother and dominated by vast mare plains, while the far side is rugged and mountainous. By analysing data from the GRAIL mission, scientists discovered that these surface differences stem from deep internal disparities in how each hemisphere responds to Earth’s tidal pull. That is great for understanding the evolution of solid bodies in the Solar System, but there is also a very pragmatic reason to do this work. It will be key to the future human exploration of the Moon.

“We found that the Moon’s near side is flexing more than the far side, meaning there’s something fundamentally different about the internal structure of the Moon’s near side compared to its far side,” said Park. “When we first analysed the data, we were so surprised by the result we didn’t believe it. So we ran the calculations many times to verify the findings. In all, this is a decade of work.” The team’s model suggests that radioactive, heat-producing elements likely accumulated beneath the near side billions of years ago, driving intense volcanic activity. This explains the vast basalt plains visible from Earth and suggests a warmer, more pliable mantle beneath the Moon’s face. Such a finding not only reshapes understanding of lunar evolution but also enhances the accuracy of future lunar navigation and mission planning. “Our study delivers the most detailed and accurate gravitational map of the Moon to date. This enhanced gravity map is a critical foundation for developing lunar Positioning, Navigation, and Timing (PNT) systems, which are essential for the success of future lunar exploration missions,” Dr Park said.

“Our technique is sensitive to any changes in the gravitational field of a body in space, whether that gravitational field changes over time, like the tidal flexing of the Moon, or through space, like a wobbling asteroid,” said Park. “Vesta wobbles as it spins, so we could measure its moment of inertia, a characteristic that is highly sensitive to the internal structure of the asteroid.” In contrast to the Moon, Vesta was expected to be a fully differentiated asteroid, with distinct layers including a metallic core, silicate mantle, and rocky crust. But analysis of its gravitational field gave a different story. Using radio and imaging data from the Dawn spacecraft, the team studied how Vesta wobbles as it spins, a behaviour tied closely to its moment of inertia. What they found was startling: Vesta’s mass is distributed more uniformly than expected, and it may possess only a small iron core, or none at all. This contradicts the prevailing “onion-layer” model of planetary formation and suggests Vesta may have formed under very different conditions, possibly from debris left by a massive collision. It also raises questions about other supposedly differentiated bodies and how varied the evolution of small planetary objects can be.

A detailed gravity map helps with navigation of spacecraft to and from the surface, as well as operations on that very surface. This work will be the basis of a large array of resources for future lunar explorers. The success of this method isn’t limited to just the Moon and Vesta. Park’s team has already applied similar gravitational modelling to Ceres and Io, revealing new insights about internal layering and volcanic activity. For Io, measurements of gravitational changes during orbit around Jupiter suggested the moon is unlikely to possess a global magma ocean, contradicting earlier theories. “Our technique isn’t restricted just to Io, Ceres, Vesta or the Moon,” said Park. “There are many opportunities in the future to apply our technique for studying the interiors of intriguing planetary bodies throughout the solar system.” As this technique continues to evolve, it offers a powerful, non-invasive tool for planetary science, capable of rewriting long-held assumptions about how worlds are built from the inside out. Whether charting the internal heat of the Moon or the surprisingly uniform bulk of Vesta, gravity is now the newest lens into the deep past of our solar system in the universe.