Scientists have uncovered fascinating new details about the internal structures of both the moon and the asteroid Vesta using gravity data collected from orbiting spacecraft.
This groundbreaking research, published in the journals Nature and Nature Astronomy, provides a deeper understanding of how these celestial bodies are formed and what they are made of—without needing to land on their surfaces.
The research teams, led by Ryan Park, a supervisor at NASA’s Jet Propulsion Laboratory, used a unique technique that analyzes how gravity varies across the moon and Vesta.
This method involves tracking the motion of spacecraft very precisely, allowing scientists to build detailed maps of each body’s gravitational field.
For the moon, the team used data from NASA’s GRAIL (Gravity Recovery and Interior Laboratory) mission, which sent two spacecraft, named Ebb and Flow, into orbit around the moon from late 2011 to the end of 2012.
The result was the most detailed lunar gravity map ever created, which can help future missions better navigate and understand the moon’s surface.
The study revealed something surprising about the moon’s interior. As the moon orbits Earth, it slightly flexes under the force of Earth’s gravity—a process called tidal deformation.
By measuring these tiny movements, the researchers found that the moon’s near side, which always faces Earth, flexes more than its far side.
This difference suggests that the near side has a warmer mantle, possibly due to volcanic activity that occurred billions of years ago. This volcanic process may have caused radioactive, heat-producing elements to gather deep inside the near side’s mantle, making it more flexible than the far side.
Park described how surprising this discovery was, explaining that when they first saw the results, the team doubted their own data.
They re-ran their calculations multiple times to be sure, and each time, the results showed the same thing: the near side of the moon is different from the far side. This research took over a decade to complete, reflecting its complexity and the careful work involved.
In a separate study, Park and his team used a similar gravity-mapping technique to examine the asteroid Vesta, which orbits between Mars and Jupiter. Data from NASA’s Dawn spacecraft, which orbited Vesta from 2011 to 2012, helped the researchers understand its internal structure.
Unlike Earth or even the moon, which have distinct layers like a core, mantle, and crust, Vesta appeared to be mostly uniform inside. Scientists had long believed that Vesta was made up of layers, with a dense iron core.
But Park’s team found evidence suggesting Vesta may not have these layers at all. Instead, its interior seems to be much more evenly spread out, with perhaps only a tiny iron core or none at all.
Understanding Vesta’s structure was possible because of its slight wobble as it spins, which the team measured to estimate its moment of inertia.
This characteristic, similar to how a spinning ice skater speeds up when pulling in their arms, reveals how Vesta’s mass is distributed. The results suggest that Vesta may have formed differently than scientists originally thought.
This method of using gravity to peer inside planets and asteroids is not limited to just the moon and Vesta. Park’s team has already applied it to the dwarf planet Ceres and Jupiter’s volcanic moon Io, uncovering new information about their interiors as well.
Park believes that this approach will allow scientists to explore the hidden structures of many other planetary bodies across the solar system in the years to come.
These studies are reshaping our understanding of how moons and asteroids form and evolve, revealing hidden secrets about the solar system that were previously impossible to see.
