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| This image illustrates the Moon’s hot interior and ancient volcanism that shaped the near side’s vast plains, known as mare, about 2 to 3 billion years ago. |
NASA scientists have unveiled groundbreaking insights into the Moon and asteroid Vesta’s internal structures using advanced gravity modeling techniques—no landings required.
In two recent studies led by Ryan Park of NASA’s Jet Propulsion Laboratory, researchers analyzed subtle changes in spacecraft motion to map how gravity varies across planetary bodies. The findings, published in Nature and Nature Astronomy, showcase how tracking gravity can unravel hidden geological processes and formation histories.
Lunar Flexing Sheds Light on Internal Heat.
The Moon study, published on May 14, used data from NASA’s GRAIL mission, where twin spacecraft Ebb and Flow orbited the Moon from late 2011 to 2012. Researchers developed a new lunar gravity model, capturing tiny variations in the Moon’s gravity as it orbits Earth in an elliptical path. These fluctuations cause the Moon to flex—a phenomenon known as tidal deformation.
This flexing isn’t symmetrical. The Moon’s near side, dominated by smooth volcanic plains called mare, deforms more than the rugged far side. This asymmetry, the study suggests, stems from differences deep below the surface. The near side likely harbors a warmer mantle enriched with heat-producing radioactive elements, offering compelling evidence for ancient volcanic activity.
“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,” said Park. “We ran the calculations multiple times—it’s a surprising and significant finding.”
The team’s detailed gravity map could also help future missions navigate the Moon with improved precision in timing and positioning.
Vesta’s Surprising Uniformity.
In a parallel study of Vesta, published on April 23, researchers examined gravity data from NASA’s Dawn spacecraft, which orbited the asteroid between 2011 and 2012. Instead of discovering a well-layered structure with a dense core—as many models predicted—the team found Vesta to be surprisingly uniform inside.
By measuring the asteroid’s moment of inertia, influenced by how it wobbles while rotating, they deduced that Vesta’s mass is more evenly spread than expected. This contradicts previous theories suggesting Vesta formed in layered stages like an onion, possibly indicating it didn’t fully differentiate or was shaped by a colossal collision.
“Gravity is a unique and fundamental property of a planetary body,” said Park. “It tells us what’s happening deep inside, and we can access that just by precisely tracking spacecraft motion.”
Looking Beyond: Ceres, Io, and More.
Park’s team has applied this gravity analysis method to other celestial bodies as well. In 2016, they examined Ceres, another target of the Dawn mission, and suggested a partially layered interior. More recently, they analyzed Jupiter’s moon Io using data from NASA’s Juno and Galileo missions. The findings indicate Io likely lacks a global magma ocean beneath its highly volcanic surface.
The technique’s power lies in its versatility—it doesn’t require landers or seismic equipment. Instead, it relies on supercomputers, precise tracking, and deep data analysis to uncover a world’s inner secrets.
There are many opportunities in the future to apply our technique,” said Park. “Whether it’s moons, asteroids, or dwarf planets, gravity gives us a window into how these worlds formed and evolved.